#antennas — Public Fediverse posts

The magic carpet ground plane is grounded, but the GTU keeps flying.

Ham Radio Outside the Box receives quite a lot of email every week from readers with questions, comments and suggestions. One such email came about as a result of an article in the outstanding newsletter from the Surrey Amateur Radio Club called the Communicator. The editor of the Communicator is Canadian Amateur Radio Hall of Fame member John Schouten VE7TI. John approached me some time ago to see if I would be willing to be a regular contributor to the Communicator. I readily accepted and I am indebted to the Communicator for publishing a regular series of posts from this blog to the Communicator’s international readers in over 150 countries.

A recent article in the Communicator triggered an email from Guy VA7GI and that sparked a chain of correspondence beginning with a request for more details of the Ground Tuning Unit featured in recent posts on this blog. Then Guy suggested I conduct a test to compare a GTU combined with a Faraday cloth (“Magic Carpet”) capacitance plate on the ground, to a regular set of radials. That sounded like an interesting challenge so I set up a test antenna out in the backyard to find out how the two compared.

An old, bruised and battered, long retired MFJ 20m telescopic whip was mounted on a tripod and promptly caught a gust of wind which sent it crashing to the ground. Fortunately it just missed a large birch tree and landed softly on the grass. More bruises! It was re-erected and secured with cordage to prevent any further falls. Then a 17ft raised wire counterpoise was attached via an RF current sensor.

RF was applied to the antenna by a RigExpert antenna analyzer and a strong deflection was observed on the current sensor. The meter reading was set to mid-scale by adjusting the instrument’s sensitivity control. Now it would be possible to determine whether the current through the GTU/Faraday cloth was higher or lower than the current passing into the wire counterpoise.

Next step; the counterpoise wire was disconnected and the GTU was attached with a wire to the Faraday cloth on the ground. Once again RF was applied and the relative current was observed on the meter. NB: the current sensor does not measure absolute current values; its job is only to compare relative values. I expected the GTU/Faraday cloth ground arrangement to compare favorably with the wire counterpoise, after all I had made multiple contacts with this arrangement. But, to my surprise, the ground current was now lower than the wire counterpoise result.

My “magic carpet”, made of Faraday cloth ordered from the company named after a Brazilian River, was a purchase made for the purpose of experimentation. To its credit, it served its purpose, but I had some reservations about its suitability for field portable radio operations. The first time I laid it out on my backyard lawn was during a day of bright sunshine. I was dazzled by the sunlight reflected from its surface. Those reflections were probably observable from Earth orbit and certainly detracted from the stealth of a field installation. Stealth was restored with a coat of dark green, non-reflective spray paint.

The outdoor environment challenged the installation with another trial – wind. The wind had already laid the antenna whip down, now it blew under and around my one square meter of Faraday cloth making it difficult to secure it to the ground. No spring gusts were going to defeat this scientific experiment, so reinforced grommets were attached to each corner of the cloth which was then tightly and securely held in its place with tent stakes.

After a few deployments the edges of the Faraday cloth began to fray and were secured with Gorilla tape, but the non-reflective paint was beginning to crack where the magic carpet was folded between uses. And then it failed the current test!

The image shows the Ham Radio Outside the Box Linear-Loaded Monopole with Magic Carpet deployed along the shore of Lake Huron during a recent OOTA activation. No, that’s not a typo, OOTA is “Out On The Air”. Check it out online.

So is the Magic Carpet idea dead in the water? Guy VA7GI had another suggestion: “I have two friends with ham rigs on sailboats. They each use a backstay with insulators as a vertical antenna. You’d think with a saltwater ground they have the perfect ground plane. But it’s not that simple. They use folded copper wire in the bilge for a ground. They don’t want to drill a hole in the hull or dangle a wire near the prop. Alternatively, they could use Faraday cloth and your GTU. I bet that’d make a huge difference, especially for trans-ocean sailing.”

So magic carpet rides on the wayward wind are grounded, at least for now. My home QTH is surrounded by the Great Lakes so maybe the the idea of a “floating ground” is worth exploring?

The magic carpet is grounded, but not the GTU!

In a later email Guy VA7GI said: “My intuition is that most verticals have compromised radials, placed wherever convenient or possible. Perhaps all vertical antennas would benefit from a GTU.” On the first point Guy may be right. There is a lot of discussion online about the placement of radials. On the ground, or raised above ground? Positioned to direct an antenna’s radiation in a particular direction? Or spread evenly to enhance the widest ground coupling? And, of course, how many radials?

Guy’s second point: “Perhaps all vertical antennas would benefit from a GTU” got me thinking. Could that idea be of benefit in implementing a limited footprint, vertical quarter-wave field antenna? How does a Ground Tuning Unit work? It resonates a capacitive ground path which increases the current in “the other half” of an antenna. That is an idea worth exploring, so a further test was conducted.

A new, improved linear-loaded monopole was erected. The ham-made ladder line previously used has been replaced with a slightly longer (11.5ft) section of 450 ohm commercial window line. When erected as a quarter-wave vertical worked against a GTU tuned counterpoise, the length is not critical within certain restraints because the electrical length of “the other half” is adjustable by the GTU. A shorter radiating element with a longer counterpoise works, as does a longer radiator with a shorter counterpoise. The antenna impedance changes, but unless taken to extremes, it remains close enough to keep the SWR presented to the transceiver within acceptable limits.

This new test was designed to discover whether a GTU could resonate short raised radials sufficiently well to make the antenna an efficient radiator. This arrangement would get a passing grade if the current through the GTU/short radials combination matched the current passing through full-length radials. It didn’t work out too well with the Faraday cloth so I was skeptical about the outcome of this test.

My 11.5ft linear-loaded monopole was paired with two raised radials each 16.5ft long but with links at 11ft and 13ft. Once again, the current was monitored with the full-length radials and set to mid-scale on the meter as a benchmark. Then the radial links were opened at the 11ft point and the GTU was adjusted for maximum current. This time there was a different outcome. The current matched the result obtained with the full-length radials. So Guy – you were right!

Further tests will be conducted with even shorter raised radials to determine whether the current can be maintained with a minimum possible ground footprint. The objective is to design a simple pedestrian portable antenna that can be deployed in a limited space environment such as small clearings in the woods.

The man from the future

Another project remains on the slate and that is the idea of using a helically wound radiating element as suggested by a reader in New Zealand (the “man from the future” – New Zealand is 16 hours ahead of the Eastern Time Zone). Ham Radio Outside the Box will cover that in a later post.

Meanwhile a package arrived in the mail

I was very pleased to receive a package in the mail from Tim KQ4TQ. Tim sent me a GTU he had built himself and asked me to evaluate it. Tim’s GTU is a slightly different build to my own and I will certainly evaluate it fully and report back here soon. Thanks Tim!

Thanks to all Ham Radio Outside the Box subscribers

I put a lot of work into preparing posts for this blog, but it is a labor of love. I seek no financial return, nor will I accept any; this is a hobby not a business. My motivation is to stimulate discussion and learn from experiments and the feedback of other hams. So it was gratifying when WordPress informed me recently that Ham Radio Outside the Box has now surpassed the modest level of 1000 subscribers. Knowing there is a steadily growing interest in the content generated here makes all the work worthwhile. Thank you!

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

A Mini Ground Tuning Unit and a magic carpet for portable ops

In the last couple of posts I discussed my quest for a simple portable antenna that could be rapidly deployed in a very limited space, for example in a small clearing while hiking through the woods. Such an antenna would have to be a short, yet efficient, vertical that occupies a very small footprint on the ground.

The first successful candidate is a Linear-Loaded Monopole which meets all the design criteria and has performed surprisingly well in initial field tests. Ham Radio Outside the Box has received another suggestion from a reader who lives in the future (I’ll explain in an upcoming post) for a helical antenna. We’ll be hitting the outback (out in the backyard) to experiment with that idea very shortly.

Meanwhile, another design criterion is that a hiking antenna should occupy a very small footprint on the ground. My local woodlands sit atop the Niagara Escarpment and are often very rocky – sometimes with wide and dangerous cracks in the bedrock. There is often nowhere to set up ground radials and limited options for raised radials, so an alternative arrangement for “the other half” of a vertical quarter-wave antenna is necessary.

The solution that has been discussed here on Ham Radio Outside the Box is to use a Ground Tuning Unit (GTU) coupled to a small capacitive plate on the ground. There is some spooky physics associated with how a GTU works which we’ll discuss later in this post. But don’t let that discourage you; the science of physics is full of mind-mending spooky stuff.

Introducing the Mini GTU

I built a GTU some years ago which has seen a lot of use. Unfortunately it is rather big for carrying on a hike through the woods. I needed a small, lightweight version for this new use case. The Mini GTU is a simple device as can be seen from the wiring diagram here:

The device comprises four inductances – 4, 2, 1 and 0.5 microhenries. Each inductor has a SPST switch that can be used to short circuit it and thereby bypass it from the inductance selection. This arrangement allows binary selection of inductance from 0.5 to 7.5 microhenries in 0.5 microhenry increments. For this application it was considered unnecessary to increase the inductance any further, but more inductance could be added by doubling the value of each added inductor.

The Mini GTU is connected to the shield side of the coax that connects the antenna to the radio. This is exactly where you would normally connect radials. The other end of the Mini GTU connects to a capacitive plate laid directly on the ground.

What? No ground current meter?

A GTU usually has a ground current meter in series with the current path. That is achieved by adding a sampling circuit – a small toroidal core inductor with a single secondary turn, a diode rectifier and meter. Again, unnecessary in this application because as the current through the GTU increases, so does the current in the radiating part of the antenna. This is indicated by observing the SWR indicator on the radio.

Construction of the Mini GTU

I built the device on a small piece of perfboard. The following two pictures show the layout of the components. As usual, my collection of T37-2 and T37-6 powdered iron cores were deployed. The smallest inductor (0.5uH) was wound on two stacked T37-6 cores. The 1uH and 2uH inductors were each wound on two stacked T37-2 cores. For the 4uH inductor I redeployed the six T37-2 binocular style cores I had used on the 2T2C inductor discussed in a recent post.

Why not just use one tapped inductor and a rotary switch?

That’s a good question. I could have wound a single 7.5 uH inductor with taps every 0.5 microhenries and used a rotary switch to select the appropriate inductance. But that would require good precision in locating the tap points since 0.5uH is a very small inductance that is more easily wound on a small core.

It is unnecessary to wind these smaller inductors to the precise values specified. Even using tiny T37 cores, a single turn can change the inductance quite a bit. I strove for a precision of about 10% which turned out to be very achievable.

About that capacitive plate on the ground …

Various different types of plate were tried. Pizza trays, hardware cloth and chicken wire all sorta worked. I wasn’t happy with any of them though. They are not very easily carried on a hike and one, the hardware cloth, had sharp cut steel wire edges that attacked me viciously when I handled it. A better solution had to be found.

Why don’t you come with me … on a magic carpet ride

I bought a piece of Faraday cloth to try out. This material is very light and easy to pack away in a backpack while hiking. Faraday cloth is sometimes referred to as “magic carpet” in ham radio circles and perhaps with good reason. It is made of several layers with interwoven dense conducting material. I purchased a piece of magic carpet from the “Brazilian River” company. It measures 39×43 inches (very nearly 1 square meter).

One square meter is a little larger than I had hoped for in this application so I folded it twice to created a nearly square smaller footprint. If that worked the plan was to cut the sheet into four pieces and use just a single piece for my hiking antenna. Did it work? With the smallest footprint and adjustment of the Mini GTU for best SWR indication on the radio an SWR of 1.68:1 was obtained. Not bad, in fact very usable, but could a bigger magic carpet go even better?

Second test: the magic carpet was folded in half. Now it was a rectangle and with the Mini GTU adjusted the best SWR dropped to 1.45:1. Obviously a trend had been established. Could the whole sheet of magic carpet top the trend?

Third test: now the whole square meter of Faraday cloth lay spread on the ground, secured from the wind with some rocks surreptitiously borrowed from my wife’s garden bed (thanks to all the ancient Norse gods she doesn’t read my blog). The SWR dropped again to 1.13:1. Jingolaba!

Conclusion: “magic carpet” seems to be best solution. If the available trail-side operating site is too small for the whole one square meter of cloth, it can be folded once or even twice while keeping the SWR well below 2:1.

Other hams have tried even larger sheets of Faraday cloth for a ground plane and achieved good results, but without a GTU. The advantage of the GTU is that only a very small capacitive ground plate is required to achieve the same or better results.

One more final note: antenna physicists will note I have been using SWR as a measurement of the effectiveness of the hiking antenna. Of course, lowest SWR does not imply resonance, but radios do not have any way of measuring and displaying complex impedance values and an antenna analyzer would add to the weight needed to be carried into the field when hiking.

Addendum: a bit of spooky physics to (explain?) how a GTU works

A quarter-wave vertical antenna radiates sinusoidal voltage and current waves into an imaginary medium called the “ether”. At the same time a mirror image of these waves is generated in the ground. These mirror image waves are as real as the “ether”. If we were to bury a current meter in the ground beneath the antenna would it record the mirror image? Unrenowned scientists like myself (I earned a bachelor’s degree in physics way back when) say no.

There are three reasons why not. First, and most obvious, we cannot read a meter buried in the ground. Second, no because the mirror image is virtual not real. And the third reason is really spooky. If you search on the Whirled Wild Web for the “double slit” experiment you will learn that spooky physics stuff only happens when scientists don’t try to monitor it. That experiment is one of the most mind-bending, unexplained phenomena that even amateur scientists can attempt to reproduce. So what happens to the real current flowing through the GTU? RF gotta go somewhere.

The concept of virtual images can be seen in this picture of looking at a transceiver in a mirror. If we trace the path of the light rays through the mirror we can see a mirror image of the transceiver at the same distance behind the mirror as the actual transceiver is in front of the mirror. Step behind the mirror and you won’t find the virtual mirror image. A fanciful thought emerges here. Maybe science will one day find a way to create that expensive radio you can’t afford using a virtual image held behind a mirror.

Physics can take spookiness to extremes. My own favorite is a topic called quantum entanglement. If really mind-bending science interests you, try typing that into your search engine. Even one of the greatest scientific minds of all time, Albert Einstein, called that “spooky action at a distance”.

Back to the future

My next project will be developing this week. I replied to the reader “from the future” and will be exploring his ideas in my backyard where intermittent snow cover is heralding the very slow birth of another spring season. Stayed tuned.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

A Mini Ground Tuning Unit and a magic carpet for portable ops

In the last couple of posts I discussed my quest for a simple portable antenna that could be rapidly deployed in a very limited space, for example in a small clearing while hiking through the woods. Such an antenna would have to be a short, yet efficient, vertical that occupies a very small footprint on the ground.

The first successful candidate is a Linear-Loaded Monopole which meets all the design criteria and has performed surprisingly well in initial field tests. Ham Radio Outside the Box has received another suggestion from a reader who lives in the future (I’ll explain in an upcoming post) for a helical antenna. We’ll be hitting the outback (out in the backyard) to experiment with that idea very shortly.

Meanwhile, another design criterion is that a hiking antenna should occupy a very small footprint on the ground. My local woodlands sit atop the Niagara Escarpment and are often very rocky – sometimes with wide and dangerous cracks in the bedrock. There is often nowhere to set up ground radials and limited options for raised radials, so an alternative arrangement for “the other half” of a vertical quarter-wave antenna is necessary.

The solution that has been discussed here on Ham Radio Outside the Box is to use a Ground Tuning Unit (GTU) coupled to a small capacitive plate on the ground. There is some spooky physics associated with how a GTU works which we’ll discuss later in this post. But don’t let that discourage you; the science of physics is full of mind-mending spooky stuff.

Introducing the Mini GTU

I built a GTU some years ago which has seen a lot of use. Unfortunately it is rather big for carrying on a hike through the woods. I needed a small, lightweight version for this new use case. The Mini GTU is a simple device as can be seen from the wiring diagram here:

The device comprises four inductances – 4, 2, 1 and 0.5 microhenries. Each inductor has a SPST switch that can be used to short circuit it and thereby bypass it from the inductance selection. This arrangement allows binary selection of inductance from 0.5 to 7.5 microhenries in 0.5 microhenry increments. For this application it was considered unnecessary to increase the inductance any further, but more inductance could be added by doubling the value of each added inductor.

The Mini GTU is connected to the shield side of the coax that connects the antenna to the radio. This is exactly where you would normally connect radials. The other end of the Mini GTU connects to a capacitive plate laid directly on the ground.

What? No ground current meter?

A GTU usually has a ground current meter in series with the current path. That is achieved by adding a sampling circuit – a small toroidal core inductor with a single secondary turn, a diode rectifier and meter. Again, unnecessary in this application because as the current through the GTU increases, so does the current in the radiating part of the antenna. This is indicated by observing the SWR indicator on the radio.

Construction of the Mini GTU

I built the device on a small piece of perfboard. The following two pictures show the layout of the components. As usual, my collection of T37-2 and T37-6 powdered iron cores were deployed. The smallest inductor (0.5uH) was wound on two stacked T37-6 cores. The 1uH and 2uH inductors were each wound on two stacked T37-2 cores. For the 4uH inductor I redeployed the six T37-2 binocular style cores I had used on the 2T2C inductor discussed in a recent post.

Why not just use one tapped inductor and a rotary switch?

That’s a good question. I could have wound a single 7.5 uH inductor with taps every 0.5 microhenries and used a rotary switch to select the appropriate inductance. But that would require good precision in locating the tap points since 0.5uH is a very small inductance that is more easily wound on a small core.

It is unnecessary to wind these smaller inductors to the precise values specified. Even using tiny T37 cores, a single turn can change the inductance quite a bit. I strove for a precision of about 10% which turned out to be very achievable.

About that capacitive plate on the ground …

Various different types of plate were tried. Pizza trays, hardware cloth and chicken wire all sorta worked. I wasn’t happy with any of them though. They are not very easily carried on a hike and one, the hardware cloth, had sharp cut steel wire edges that attacked me viciously when I handled it. A better solution had to be found.

Why don’t you come with me … on a magic carpet ride

I bought a piece of Faraday cloth to try out. This material is very light and easy to pack away in a backpack while hiking. Faraday cloth is sometimes referred to as “magic carpet” in ham radio circles and perhaps with good reason. It is made of several layers with interwoven dense conducting material. I purchased a piece of magic carpet from the “Brazilian River” company. It measures 39×43 inches (very nearly 1 square meter).

One square meter is a little larger than I had hoped for in this application so I folded it twice to created a nearly square smaller footprint. If that worked the plan was to cut the sheet into four pieces and use just a single piece for my hiking antenna. Did it work? With the smallest footprint and adjustment of the Mini GTU for best SWR indication on the radio an SWR of 1.68:1 was obtained. Not bad, in fact very usable, but could a bigger magic carpet go even better?

Second test: the magic carpet was folded in half. Now it was a rectangle and with the Mini GTU adjusted the best SWR dropped to 1.45:1. Obviously a trend had been established. Could the whole sheet of magic carpet top the trend?

Third test: now the whole square meter of Faraday cloth lay spread on the ground, secured from the wind with some rocks surreptitiously borrowed from my wife’s garden bed (thanks to all the ancient Norse gods she doesn’t read my blog). The SWR dropped again to 1.13:1. Jingolaba!

Conclusion: “magic carpet” seems to be best solution. If the available trail-side operating site is too small for the whole one square meter of cloth, it can be folded once or even twice while keeping the SWR well below 2:1.

Other hams have tried even larger sheets of Faraday cloth for a ground plane and achieved good results, but without a GTU. The advantage of the GTU is that only a very small capacitive ground plate is required to achieve the same or better results.

One more final note: antenna physicists will note I have been using SWR as a measurement of the effectiveness of the hiking antenna. Of course, lowest SWR does not imply resonance, but radios do not have any way of measuring and displaying complex impedance values and an antenna analyzer would add to the weight needed to be carried into the field when hiking.

Addendum: a bit of spooky physics to (explain?) how a GTU works

A quarter-wave vertical antenna radiates sinusoidal voltage and current waves into an imaginary medium called the “ether”. At the same time a mirror image of these waves is generated in the ground. These mirror image waves are as real as the “ether”. If we were to bury a current meter in the ground beneath the antenna would it record the mirror image? Unrenowned scientists like myself (I earned a bachelor’s degree in physics way back when) say no.

There are three reasons why not. First, and most obvious, we cannot read a meter buried in the ground. Second, no because the mirror image is virtual not real. And the third reason is really spooky. If you search on the Whirled Wild Web for the “double slit” experiment you will learn that spooky physics stuff only happens when scientists don’t try to monitor it. That experiment is one of the most mind-bending, unexplained phenomena that even amateur scientists can attempt to reproduce. So what happens to the real current flowing through the GTU? RF gotta go somewhere.

The concept of virtual images can be seen in this picture of looking at a transceiver in a mirror. If we trace the path of the light rays through the mirror we can see a mirror image of the transceiver at the same distance behind the mirror as the actual transceiver is in front of the mirror. Step behind the mirror and you won’t find the virtual mirror image. A fanciful thought emerges here. Maybe science will one day find a way to create that expensive radio you can’t afford using a virtual image held behind a mirror.

Physics can take spookiness to extremes. My own favorite is a topic called quantum entanglement. If really mind-bending science interests you, try typing that into your search engine. Even one of the greatest scientific minds of all time, Albert Einstein, called that “spooky action at a distance”.

Back to the future

My next project will be developing this week. I replied to the reader “from the future” and will be exploring his ideas in my backyard where intermittent snow cover is heralding the very slow birth of another spring season. Stayed tuned.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

A Mini Ground Tuning Unit and a magic carpet for portable ops

In the last couple of posts I discussed my quest for a simple portable antenna that could be rapidly deployed in a very limited space, for example in a small clearing while hiking through the woods. Such an antenna would have to be a short, yet efficient, vertical that occupies a very small footprint on the ground.

The first successful candidate is a Linear-Loaded Monopole which meets all the design criteria and has performed surprisingly well in initial field tests. Ham Radio Outside the Box has received another suggestion from a reader who lives in the future (I’ll explain in an upcoming post) for a helical antenna. We’ll be hitting the outback (out in the backyard) to experiment with that idea very shortly.

Meanwhile, another design criterion is that a hiking antenna should occupy a very small footprint on the ground. My local woodlands sit atop the Niagara Escarpment and are often very rocky – sometimes with wide and dangerous cracks in the bedrock. There is often nowhere to set up ground radials and limited options for raised radials, so an alternative arrangement for “the other half” of a vertical quarter-wave antenna is necessary.

The solution that has been discussed here on Ham Radio Outside the Box is to use a Ground Tuning Unit (GTU) coupled to a small capacitive plate on the ground. There is some spooky physics associated with how a GTU works which we’ll discuss later in this post. But don’t let that discourage you; the science of physics is full of mind-mending spooky stuff.

Introducing the Mini GTU

I built a GTU some years ago which has seen a lot of use. Unfortunately it is rather big for carrying on a hike through the woods. I needed a small, lightweight version for this new use case. The Mini GTU is a simple device as can be seen from the wiring diagram here:

The device comprises four inductances – 4, 2, 1 and 0.5 microhenries. Each inductor has a SPST switch that can be used to short circuit it and thereby bypass it from the inductance selection. This arrangement allows binary selection of inductance from 0.5 to 7.5 microhenries in 0.5 microhenry increments. For this application it was considered unnecessary to increase the inductance any further, but more inductance could be added by doubling the value of each added inductor.

The Mini GTU is connected to the shield side of the coax that connects the antenna to the radio. This is exactly where you would normally connect radials. The other end of the Mini GTU connects to a capacitive plate laid directly on the ground.

What? No ground current meter?

A GTU usually has a ground current meter in series with the current path. That is achieved by adding a sampling circuit – a small toroidal core inductor with a single secondary turn, a diode rectifier and meter. Again, unnecessary in this application because as the current through the GTU increases, so does the current in the radiating part of the antenna. This is indicated by observing the SWR indicator on the radio.

Construction of the Mini GTU

I built the device on a small piece of perfboard. The following two pictures show the layout of the components. As usual, my collection of T37-2 and T37-6 powdered iron cores were deployed. The smallest inductor (0.5uH) was wound on two stacked T37-6 cores. The 1uH and 2uH inductors were each wound on two stacked T37-2 cores. For the 4uH inductor I redeployed the six T37-2 binocular style cores I had used on the 2T2C inductor discussed in a recent post.

Why not just use one tapped inductor and a rotary switch?

That’s a good question. I could have wound a single 7.5 uH inductor with taps every 0.5 microhenries and used a rotary switch to select the appropriate inductance. But that would require good precision in locating the tap points since 0.5uH is a very small inductance that is more easily wound on a small core.

It is unnecessary to wind these smaller inductors to the precise values specified. Even using tiny T37 cores, a single turn can change the inductance quite a bit. I strove for a precision of about 10% which turned out to be very achievable.

About that capacitive plate on the ground …

Various different types of plate were tried. Pizza trays, hardware cloth and chicken wire all sorta worked. I wasn’t happy with any of them though. They are not very easily carried on a hike and one, the hardware cloth, had sharp cut steel wire edges that attacked me viciously when I handled it. A better solution had to be found.

Why don’t you come with me … on a magic carpet ride

I bought a piece of Faraday cloth to try out. This material is very light and easy to pack away in a backpack while hiking. Faraday cloth is sometimes referred to as “magic carpet” in ham radio circles and perhaps with good reason. It is made of several layers with interwoven dense conducting material. I purchased a piece of magic carpet from the “Brazilian River” company. It measures 39×43 inches (very nearly 1 square meter).

One square meter is a little larger than I had hoped for in this application so I folded it twice to created a nearly square smaller footprint. If that worked the plan was to cut the sheet into four pieces and use just a single piece for my hiking antenna. Did it work? With the smallest footprint and adjustment of the Mini GTU for best SWR indication on the radio an SWR of 1.68:1 was obtained. Not bad, in fact very usable, but could a bigger magic carpet go even better?

Second test: the magic carpet was folded in half. Now it was a rectangle and with the Mini GTU adjusted the best SWR dropped to 1.45:1. Obviously a trend had been established. Could the whole sheet of magic carpet top the trend?

Third test: now the whole square meter of Faraday cloth lay spread on the ground, secured from the wind with some rocks surreptitiously borrowed from my wife’s garden bed (thanks to all the ancient Norse gods she doesn’t read my blog). The SWR dropped again to 1.13:1. Jingolaba!

Conclusion: “magic carpet” seems to be best solution. If the available trail-side operating site is too small for the whole one square meter of cloth, it can be folded once or even twice while keeping the SWR well below 2:1.

Other hams have tried even larger sheets of Faraday cloth for a ground plane and achieved good results, but without a GTU. The advantage of the GTU is that only a very small capacitive ground plate is required to achieve the same or better results.

One more final note: antenna physicists will note I have been using SWR as a measurement of the effectiveness of the hiking antenna. Of course, lowest SWR does not imply resonance, but radios do not have any way of measuring and displaying complex impedance values and an antenna analyzer would add to the weight needed to be carried into the field when hiking.

Addendum: a bit of spooky physics to (explain?) how a GTU works

A quarter-wave vertical antenna radiates sinusoidal voltage and current waves into an imaginary medium called the “ether”. At the same time a mirror image of these waves is generated in the ground. These mirror image waves are as real as the “ether”. If we were to bury a current meter in the ground beneath the antenna would it record the mirror image? Unrenowned scientists like myself (I earned a bachelor’s degree in physics way back when) say no.

There are three reasons why not. First, and most obvious, we cannot read a meter buried in the ground. Second, no because the mirror image is virtual not real. And the third reason is really spooky. If you search on the Whirled Wild Web for the “double slit” experiment you will learn that spooky physics stuff only happens when scientists don’t try to monitor it. That experiment is one of the most mind-bending, unexplained phenomena that even amateur scientists can attempt to reproduce. So what happens to the real current flowing through the GTU? RF gotta go somewhere.

The concept of virtual images can be seen in this picture of looking at a transceiver in a mirror. If we trace the path of the light rays through the mirror we can see a mirror image of the transceiver at the same distance behind the mirror as the actual transceiver is in front of the mirror. Step behind the mirror and you won’t find the virtual mirror image. A fanciful thought emerges here. Maybe science will one day find a way to create that expensive radio you can’t afford using a virtual image held behind a mirror.

Physics can take spookiness to extremes. My own favorite is a topic called quantum entanglement. If really mind-bending science interests you, try typing that into your search engine. Even one of the greatest scientific minds of all time, Albert Einstein, called that “spooky action at a distance”.

Back to the future

My next project will be developing this week. I replied to the reader “from the future” and will be exploring his ideas in my backyard where intermittent snow cover is heralding the very slow birth of another spring season. Stayed tuned.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

A Mini Ground Tuning Unit and a magic carpet for portable ops

In the last couple of posts I discussed my quest for a simple portable antenna that could be rapidly deployed in a very limited space, for example in a small clearing while hiking through the woods. Such an antenna would have to be a short, yet efficient, vertical that occupies a very small footprint on the ground.

The first successful candidate is a Linear-Loaded Monopole which meets all the design criteria and has performed surprisingly well in initial field tests. Ham Radio Outside the Box has received another suggestion from a reader who lives in the future (I’ll explain in an upcoming post) for a helical antenna. We’ll be hitting the outback (out in the backyard) to experiment with that idea very shortly.

Meanwhile, another design criterion is that a hiking antenna should occupy a very small footprint on the ground. My local woodlands sit atop the Niagara Escarpment and are often very rocky – sometimes with wide and dangerous cracks in the bedrock. There is often nowhere to set up ground radials and limited options for raised radials, so an alternative arrangement for “the other half” of a vertical quarter-wave antenna is necessary.

The solution that has been discussed here on Ham Radio Outside the Box is to use a Ground Tuning Unit (GTU) coupled to a small capacitive plate on the ground. There is some spooky physics associated with how a GTU works which we’ll discuss later in this post. But don’t let that discourage you; the science of physics is full of mind-mending spooky stuff.

Introducing the Mini GTU

I built a GTU some years ago which has seen a lot of use. Unfortunately it is rather big for carrying on a hike through the woods. I needed a small, lightweight version for this new use case. The Mini GTU is a simple device as can be seen from the wiring diagram here:

The device comprises four inductances – 4, 2, 1 and 0.5 microhenries. Each inductor has a SPST switch that can be used to short circuit it and thereby bypass it from the inductance selection. This arrangement allows binary selection of inductance from 0.5 to 7.5 microhenries in 0.5 microhenry increments. For this application it was considered unnecessary to increase the inductance any further, but more inductance could be added by doubling the value of each added inductor.

The Mini GTU is connected to the shield side of the coax that connects the antenna to the radio. This is exactly where you would normally connect radials. The other end of the Mini GTU connects to a capacitive plate laid directly on the ground.

What? No ground current meter?

A GTU usually has a ground current meter in series with the current path. That is achieved by adding a sampling circuit – a small toroidal core inductor with a single secondary turn, a diode rectifier and meter. Again, unnecessary in this application because as the current through the GTU increases, so does the current in the radiating part of the antenna. This is indicated by observing the SWR indicator on the radio.

Construction of the Mini GTU

I built the device on a small piece of perfboard. The following two pictures show the layout of the components. As usual, my collection of T37-2 and T37-6 powdered iron cores were deployed. The smallest inductor (0.5uH) was wound on two stacked T37-6 cores. The 1uH and 2uH inductors were each wound on two stacked T37-2 cores. For the 4uH inductor I redeployed the six T37-2 binocular style cores I had used on the 2T2C inductor discussed in a recent post.

Why not just use one tapped inductor and a rotary switch?

That’s a good question. I could have wound a single 7.5 uH inductor with taps every 0.5 microhenries and used a rotary switch to select the appropriate inductance. But that would require good precision in locating the tap points since 0.5uH is a very small inductance that is more easily wound on a small core.

It is unnecessary to wind these smaller inductors to the precise values specified. Even using tiny T37 cores, a single turn can change the inductance quite a bit. I strove for a precision of about 10% which turned out to be very achievable.

About that capacitive plate on the ground …

Various different types of plate were tried. Pizza trays, hardware cloth and chicken wire all sorta worked. I wasn’t happy with any of them though. They are not very easily carried on a hike and one, the hardware cloth, had sharp cut steel wire edges that attacked me viciously when I handled it. A better solution had to be found.

Why don’t you come with me … on a magic carpet ride

I bought a piece of Faraday cloth to try out. This material is very light and easy to pack away in a backpack while hiking. Faraday cloth is sometimes referred to as “magic carpet” in ham radio circles and perhaps with good reason. It is made of several layers with interwoven dense conducting material. I purchased a piece of magic carpet from the “Brazilian River” company. It measures 39×43 inches (very nearly 1 square meter).

One square meter is a little larger than I had hoped for in this application so I folded it twice to created a nearly square smaller footprint. If that worked the plan was to cut the sheet into four pieces and use just a single piece for my hiking antenna. Did it work? With the smallest footprint and adjustment of the Mini GTU for best SWR indication on the radio an SWR of 1.68:1 was obtained. Not bad, in fact very usable, but could a bigger magic carpet go even better?

Second test: the magic carpet was folded in half. Now it was a rectangle and with the Mini GTU adjusted the best SWR dropped to 1.45:1. Obviously a trend had been established. Could the whole sheet of magic carpet top the trend?

Third test: now the whole square meter of Faraday cloth lay spread on the ground, secured from the wind with some rocks surreptitiously borrowed from my wife’s garden bed (thanks to all the ancient Norse gods she doesn’t read my blog). The SWR dropped again to 1.13:1. Jingolaba!

Conclusion: “magic carpet” seems to be best solution. If the available trail-side operating site is too small for the whole one square meter of cloth, it can be folded once or even twice while keeping the SWR well below 2:1.

Other hams have tried even larger sheets of Faraday cloth for a ground plane and achieved good results, but without a GTU. The advantage of the GTU is that only a very small capacitive ground plate is required to achieve the same or better results.

One more final note: antenna physicists will note I have been using SWR as a measurement of the effectiveness of the hiking antenna. Of course, lowest SWR does not imply resonance, but radios do not have any way of measuring and displaying complex impedance values and an antenna analyzer would add to the weight needed to be carried into the field when hiking.

Addendum: a bit of spooky physics to (explain?) how a GTU works

A quarter-wave vertical antenna radiates sinusoidal voltage and current waves into an imaginary medium called the “ether”. At the same time a mirror image of these waves is generated in the ground. These mirror image waves are as real as the “ether”. If we were to bury a current meter in the ground beneath the antenna would it record the mirror image? Unrenowned scientists like myself (I earned a bachelor’s degree in physics way back when) say no.

There are three reasons why not. First, and most obvious, we cannot read a meter buried in the ground. Second, no because the mirror image is virtual not real. And the third reason is really spooky. If you search on the Whirled Wild Web for the “double slit” experiment you will learn that spooky physics stuff only happens when scientists don’t try to monitor it. That experiment is one of the most mind-bending, unexplained phenomena that even amateur scientists can attempt to reproduce. So what happens to the real current flowing through the GTU? RF gotta go somewhere.

The concept of virtual images can be seen in this picture of looking at a transceiver in a mirror. If we trace the path of the light rays through the mirror we can see a mirror image of the transceiver at the same distance behind the mirror as the actual transceiver is in front of the mirror. Step behind the mirror and you won’t find the virtual mirror image. A fanciful thought emerges here. Maybe science will one day find a way to create that expensive radio you can’t afford using a virtual image held behind a mirror.

Physics can take spookiness to extremes. My own favorite is a topic called quantum entanglement. If really mind-bending science interests you, try typing that into your search engine. Even one of the greatest scientific minds of all time, Albert Einstein, called that “spooky action at a distance”.

Back to the future

My next project will be developing this week. I replied to the reader “from the future” and will be exploring his ideas in my backyard where intermittent snow cover is heralding the very slow birth of another spring season. Stayed tuned.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

A Mini Ground Tuning Unit and a magic carpet for portable ops

In the last couple of posts I discussed my quest for a simple portable antenna that could be rapidly deployed in a very limited space, for example in a small clearing while hiking through the woods. Such an antenna would have to be a short, yet efficient, vertical that occupies a very small footprint on the ground.

The first successful candidate is a Linear-Loaded Monopole which meets all the design criteria and has performed surprisingly well in initial field tests. Ham Radio Outside the Box has received another suggestion from a reader who lives in the future (I’ll explain in an upcoming post) for a helical antenna. We’ll be hitting the outback (out in the backyard) to experiment with that idea very shortly.

Meanwhile, another design criterion is that a hiking antenna should occupy a very small footprint on the ground. My local woodlands sit atop the Niagara Escarpment and are often very rocky – sometimes with wide and dangerous cracks in the bedrock. There is often nowhere to set up ground radials and limited options for raised radials, so an alternative arrangement for “the other half” of a vertical quarter-wave antenna is necessary.

The solution that has been discussed here on Ham Radio Outside the Box is to use a Ground Tuning Unit (GTU) coupled to a small capacitive plate on the ground. There is some spooky physics associated with how a GTU works which we’ll discuss later in this post. But don’t let that discourage you; the science of physics is full of mind-mending spooky stuff.

Introducing the Mini GTU

I built a GTU some years ago which has seen a lot of use. Unfortunately it is rather big for carrying on a hike through the woods. I needed a small, lightweight version for this new use case. The Mini GTU is a simple device as can be seen from the wiring diagram here:

The device comprises four inductances – 4, 2, 1 and 0.5 microhenries. Each inductor has a SPST switch that can be used to short circuit it and thereby bypass it from the inductance selection. This arrangement allows binary selection of inductance from 0.5 to 7.5 microhenries in 0.5 microhenry increments. For this application it was considered unnecessary to increase the inductance any further, but more inductance could be added by doubling the value of each added inductor.

The Mini GTU is connected to the shield side of the coax that connects the antenna to the radio. This is exactly where you would normally connect radials. The other end of the Mini GTU connects to a capacitive plate laid directly on the ground.

What? No ground current meter?

A GTU usually has a ground current meter in series with the current path. That is achieved by adding a sampling circuit – a small toroidal core inductor with a single secondary turn, a diode rectifier and meter. Again, unnecessary in this application because as the current through the GTU increases, so does the current in the radiating part of the antenna. This is indicated by observing the SWR indicator on the radio.

Construction of the Mini GTU

I built the device on a small piece of perfboard. The following two pictures show the layout of the components. As usual, my collection of T37-2 and T37-6 powdered iron cores were deployed. The smallest inductor (0.5uH) was wound on two stacked T37-6 cores. The 1uH and 2uH inductors were each wound on two stacked T37-2 cores. For the 4uH inductor I redeployed the six T37-2 binocular style cores I had used on the 2T2C inductor discussed in a recent post.

Why not just use one tapped inductor and a rotary switch?

That’s a good question. I could have wound a single 7.5 uH inductor with taps every 0.5 microhenries and used a rotary switch to select the appropriate inductance. But that would require good precision in locating the tap points since 0.5uH is a very small inductance that is more easily wound on a small core.

It is unnecessary to wind these smaller inductors to the precise values specified. Even using tiny T37 cores, a single turn can change the inductance quite a bit. I strove for a precision of about 10% which turned out to be very achievable.

About that capacitive plate on the ground …

Various different types of plate were tried. Pizza trays, hardware cloth and chicken wire all sorta worked. I wasn’t happy with any of them though. They are not very easily carried on a hike and one, the hardware cloth, had sharp cut steel wire edges that attacked me viciously when I handled it. A better solution had to be found.

Why don’t you come with me … on a magic carpet ride

I bought a piece of Faraday cloth to try out. This material is very light and easy to pack away in a backpack while hiking. Faraday cloth is sometimes referred to as “magic carpet” in ham radio circles and perhaps with good reason. It is made of several layers with interwoven dense conducting material. I purchased a piece of magic carpet from the “Brazilian River” company. It measures 39×43 inches (very nearly 1 square meter).

One square meter is a little larger than I had hoped for in this application so I folded it twice to created a nearly square smaller footprint. If that worked the plan was to cut the sheet into four pieces and use just a single piece for my hiking antenna. Did it work? With the smallest footprint and adjustment of the Mini GTU for best SWR indication on the radio an SWR of 1.68:1 was obtained. Not bad, in fact very usable, but could a bigger magic carpet go even better?

Second test: the magic carpet was folded in half. Now it was a rectangle and with the Mini GTU adjusted the best SWR dropped to 1.45:1. Obviously a trend had been established. Could the whole sheet of magic carpet top the trend?

Third test: now the whole square meter of Faraday cloth lay spread on the ground, secured from the wind with some rocks surreptitiously borrowed from my wife’s garden bed (thanks to all the ancient Norse gods she doesn’t read my blog). The SWR dropped again to 1.13:1. Jingolaba!

Conclusion: “magic carpet” seems to be best solution. If the available trail-side operating site is too small for the whole one square meter of cloth, it can be folded once or even twice while keeping the SWR well below 2:1.

Other hams have tried even larger sheets of Faraday cloth for a ground plane and achieved good results, but without a GTU. The advantage of the GTU is that only a very small capacitive ground plate is required to achieve the same or better results.

One more final note: antenna physicists will note I have been using SWR as a measurement of the effectiveness of the hiking antenna. Of course, lowest SWR does not imply resonance, but radios do not have any way of measuring and displaying complex impedance values and an antenna analyzer would add to the weight needed to be carried into the field when hiking.

Addendum: a bit of spooky physics to (explain?) how a GTU works

A quarter-wave vertical antenna radiates sinusoidal voltage and current waves into an imaginary medium called the “ether”. At the same time a mirror image of these waves is generated in the ground. These mirror image waves are as real as the “ether”. If we were to bury a current meter in the ground beneath the antenna would it record the mirror image? Unrenowned scientists like myself (I earned a bachelor’s degree in physics way back when) say no.

There are three reasons why not. First, and most obvious, we cannot read a meter buried in the ground. Second, no because the mirror image is virtual not real. And the third reason is really spooky. If you search on the Whirled Wild Web for the “double slit” experiment you will learn that spooky physics stuff only happens when scientists don’t try to monitor it. That experiment is one of the most mind-bending, unexplained phenomena that even amateur scientists can attempt to reproduce. So what happens to the real current flowing through the GTU? RF gotta go somewhere.

The concept of virtual images can be seen in this picture of looking at a transceiver in a mirror. If we trace the path of the light rays through the mirror we can see a mirror image of the transceiver at the same distance behind the mirror as the actual transceiver is in front of the mirror. Step behind the mirror and you won’t find the virtual mirror image. A fanciful thought emerges here. Maybe science will one day find a way to create that expensive radio you can’t afford using a virtual image held behind a mirror.

Physics can take spookiness to extremes. My own favorite is a topic called quantum entanglement. If really mind-bending science interests you, try typing that into your search engine. Even one of the greatest scientific minds of all time, Albert Einstein, called that “spooky action at a distance”.

Back to the future

My next project will be developing this week. I replied to the reader “from the future” and will be exploring his ideas in my backyard where intermittent snow cover is heralding the very slow birth of another spring season. Stayed tuned.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Microwave bands are cool for a few reasons, but how often can you say you can fit an 8 element Yagi in the palm of your hand? #HamRadio #AmateurRadio #Antennas #13cm #Microwaves

A Linear-Loaded Monopole antenna for hiking

There is a lot of information online about Linear-Loaded Dipoles, but I haven’t found anything at all about cutting a Linear-Loaded Dipole in half to create a Linear-Loaded Monopole worked against ground. The legendary L.B. Cebik (W4RNL, SK) published a design philosophy for an 80m Linear-Loaded Monopole, but it didn’t match what I had in mind. So I decided to build one for the purpose of experimentation. Maybe I could make it into a compact, lightweight antenna capable of rapid deployment while hiking – maybe.

What is Linear-Loading?

According to my search engine’s “Search Assist”, “Linear loading is a technique used in antenna design where a portion of the antenna wire is folded back on itself to reduce its overall length while maintaining good electrical performance. This method allows for a shorter antenna that can still operate effectively on the desired frequency.”

Sounds very simple doesn’t it? In the real world, where the RF hits the ether, it gets a little more complicated – especially when venturing outside the box. I could have made life nice and simple by building a Linear-Loaded Dipole; there are lots of designs available online that I could have used. But a dipole is too large for agile, rapid deployments; it needs a taller pole which, in turn, requires pegging into the ground and guy wires. I could use a tree limb for support, but only if suitable trees are available; often they are not. No, my requirement for a very simple hiking antenna implies a vertical antenna – a short vertical antenna.

Short antennas are easy to build; simply add a loading coil at the base and Bob’s your uncle. But that won’t qualify for my purposes. Short loaded antennas have a reduced radiation resistance and ohmic loss in the coil – they are inefficient. So how to shorten an antenna while maintaining efficiency? That’s where linear loading comes into play. A linear-loaded antenna is almost as efficient as a regular version.

How to build a Linear-Loaded Monopole?

It should have been “EZ-PZ”. Just take the dimensions from any of the online designs for a Linear-Loaded Dipole and cut them in half. That’s where I started. For a 20 meter antenna, a length of around 11 feet of window line, shorted at one end, is a good starting point. I hauled it up the mast in my newly glacier-free backyard, attached a counterpoise wire and started trimming. Between snips the resonant frequency was monitored on my RigExpert antenna analyzer. I use the term “resonant frequency” loosely in this context. The expected impedance of a quarter-wave vertical is around 37 ohms which implies there will be some reactive component to the impedance. I searched for a dip in SWR over a wide frequency range until it was possible to locate where the antenna was “resonant”.

So long John?

A low SWR in the region of the bottom end of the 20 meter band was the target, but the dip in the curve was below the bottom of the band – way below. I snipped and snipped until that dip fell where it was needed. Then the counterpoise length was adjusted until the lowest SWR was obtained. How long was my ladder line? A large pile of snipped ladder line lay on the grass beneath the pole. When I took the antenna down, laid it out on the ground and measured its length it was quite a surprise to see the ladder line radiator was only 8.67ft (2.64m) long. And the counterpoise length was 18ft (5.5m).

Jingo-la-ba!

Will it QSO? I fired a smidgen less than five watts into it and received a response from a station somewhere in the US with an encouraging signal report. Well, at least it “works”. But now came the next step. That pesky 18ft counterpoise had to go, to be replaced with the 2T2C (Tuned Tank Circuit Coupler) described in the last post.

A new challenge

The 2T2C ground coupler was directly connected to the ground side of the short coax feedline and a further wire was added to connect to a small capacitance plate on the ground. Life is complicated and then you die, so why do I insist on adding more complications? It’s called experimentation – experiment and learn! I learned. I learned that my choice of inductance and capacitance for the 2T2C resulted in impossibly sharp tuning of the ground circuit. The 2T2C needed a design modification to reduce the inductance and increase the capacitance. Spreadsheet modeling suggested this would make the 2T2C easier to adjust. I needed to confirm that before rebuilding the 2T2C, but how?

L-match innovation

The answer came in the form of a variable L-match that I built quite recently. It has switch selectable inductors and a variable capacitor. It could be adapted to fit this bill very nicely.

This idea was inspired by VK3YE who published a YouTube video about it some time ago. At one terminal of the L-match a connection is made to the BNC center conductor. At the other terminal, a connection is made to the shield side of the BNC. If you trace the signal path through the device it can be seen that the inductors and capacitor are in series. Now we have a Ground Tuning Unit (GTU) and can use binary selection of the inductances, together with rotating the variable capacitor, to determine the combination of inductance and capacitance for easiest tuning of the ground connection.

The inductances available on my L-match are 0.5, 1, 2, 4, 8 microhenries, allowing the inductance to be varied up to 15.5 microhenries in 0.5 microhenry increments. The variable capacitor is a 30-160pF polyvaricon.

Now, with the 8.67ft linear-loaded vertical erected and the “L-match GTU” making the ground connection via a capacitance plate on the ground, it was easy to select values that would allow smooth adjustment of the antenna SWR. It was found that 1 or 1.5 microhenries worked best. With these values selected the polyvaricon could be adjusted around mid-range to easily select best SWR.

A caution!

There’s a gotcha with this technique. My L-match has a switch to connect the top end of the variable capacitor to either the input or output. This is used to enable fast selection of either high or low impedance antennas. Referring to the diagram above, if the switch (not shown) is set to connect the variable capacitor to the left side of the inductors, this technique will not work. The inductors will be out of circuit and only the variable capacitor will be in circuit.

Will it still QSO?

My low-band QMX was dug out of its field pack and hooked up to the revised antenna (8.67ft of vertical window line with the “L-match GTU” providing the “other half” of the antenna. Using the “Tune SWR” feature of the QMX, the best SWR of 1.36:1 was obtained by a very small adjustment of the variable capacitor in the L-match GTU. Then it was time to go hunting. My best contact was in the state of Arizona (the “Arid Zone”?) almost 3000km away from my station in Southern Ontario. Signal reports were 599 each way. My sent report was a genuine 599 suggesting the antenna has good ears. The 599 report I received may have been genuine or perhaps it was just a “contest report”. In any event a good solid contact was made. A second contact into North Carolina only yielded a 549 signal report, but perhaps the low angle radiation pattern favored longer distance contacts.

Notice that the L-match GTU has no RF current meter. I could perhaps have inserted my home brewed RF current meter in circuit, but it wasn’t really necessary. Adjusting the ground current also regulates the radiating element current. Simply adjusting for lowest SWR indication on the radio peaks the radiated energy.

For practical outdoor use while hiking through the woods and rapidly deploying the antenna in clearings, the L-match GTU will be replaced with a much smaller series L-C coupler (2T2C). A 13ft Crappie pole is used to support the antenna. It collapses to the perfect length for carrying inside a fishing pole bag (no surprise there then) and is very lightweight.

There’s another gotcha

When the current distribution on the antenna was viewed in EZNEC it was discovered that the current maximum is in the ground circuit instead of in the radiator. Just like any ground-mounted antenna, this can lead to ground losses and inefficiency. However, the primary design objective was not to seek a Nobel Prize in antenna physics, but to come up with a design that meets the objective of a rapid deployment, simple antenna for hiking through the woods. The Linear-Loaded Monopole may just meet that requirement, but I have other ideas to try first. Stay tuned.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

A Linear-Loaded Monopole antenna for hiking

There is a lot of information online about Linear-Loaded Dipoles, but I haven’t found anything at all about cutting a Linear-Loaded Dipole in half to create a Linear-Loaded Monopole worked against ground. The legendary L.B. Cebik (W4RNL, SK) published a design philosophy for an 80m Linear-Loaded Monopole, but it didn’t match what I had in mind. So I decided to build one for the purpose of experimentation. Maybe I could make it into a compact, lightweight antenna capable of rapid deployment while hiking – maybe.

What is Linear-Loading?

According to my search engine’s “Search Assist”, “Linear loading is a technique used in antenna design where a portion of the antenna wire is folded back on itself to reduce its overall length while maintaining good electrical performance. This method allows for a shorter antenna that can still operate effectively on the desired frequency.”

Sounds very simple doesn’t it? In the real world, where the RF hits the ether, it gets a little more complicated – especially when venturing outside the box. I could have made life nice and simple by building a Linear-Loaded Dipole; there are lots of designs available online that I could have used. But a dipole is too large for agile, rapid deployments; it needs a taller pole which, in turn, requires pegging into the ground and guy wires. I could use a tree limb for support, but only if suitable trees are available; often they are not. No, my requirement for a very simple hiking antenna implies a vertical antenna – a short vertical antenna.

Short antennas are easy to build; simply add a loading coil at the base and Bob’s your uncle. But that won’t qualify for my purposes. Short loaded antennas have a reduced radiation resistance and ohmic loss in the coil – they are inefficient. So how to shorten an antenna while maintaining efficiency? That’s where linear loading comes into play. A linear-loaded antenna is almost as efficient as a regular version.

How to build a Linear-Loaded Monopole?

It should have been “EZ-PZ”. Just take the dimensions from any of the online designs for a Linear-Loaded Dipole and cut them in half. That’s where I started. For a 20 meter antenna, a length of around 11 feet of window line, shorted at one end, is a good starting point. I hauled it up the mast in my newly glacier-free backyard, attached a counterpoise wire and started trimming. Between snips the resonant frequency was monitored on my RigExpert antenna analyzer. I use the term “resonant frequency” loosely in this context. The expected impedance of a quarter-wave vertical is around 37 ohms which implies there will be some reactive component to the impedance. I searched for a dip in SWR over a wide frequency range until it was possible to locate where the antenna was “resonant”.

So long John?

A low SWR in the region of the bottom end of the 20 meter band was the target, but the dip in the curve was below the bottom of the band – way below. I snipped and snipped until that dip fell where it was needed. Then the counterpoise length was adjusted until the lowest SWR was obtained. How long was my ladder line? A large pile of snipped ladder line lay on the grass beneath the pole. When I took the antenna down, laid it out on the ground and measured its length it was quite a surprise to see the ladder line radiator was only 8.67ft (2.64m) long. And the counterpoise length was 18ft (5.5m).

Jingo-la-ba!

Will it QSO? I fired a smidgen less than five watts into it and received a response from a station somewhere in the US with an encouraging signal report. Well, at least it “works”. But now came the next step. That pesky 18ft counterpoise had to go, to be replaced with the 2T2C (Tuned Tank Circuit Coupler) described in the last post.

A new challenge

The 2T2C ground coupler was directly connected to the ground side of the short coax feedline and a further wire was added to connect to a small capacitance plate on the ground. Life is complicated and then you die, so why do I insist on adding more complications? It’s called experimentation – experiment and learn! I learned. I learned that my choice of inductance and capacitance for the 2T2C resulted in impossibly sharp tuning of the ground circuit. The 2T2C needed a design modification to reduce the inductance and increase the capacitance. Spreadsheet modeling suggested this would make the 2T2C easier to adjust. I needed to confirm that before rebuilding the 2T2C, but how?

L-match innovation

The answer came in the form of a variable L-match that I built quite recently. It has switch selectable inductors and a variable capacitor. It could be adapted to fit this bill very nicely.

This idea was inspired by VK3YE who published a YouTube video about it some time ago. At one terminal of the L-match a connection is made to the BNC center conductor. At the other terminal, a connection is made to the shield side of the BNC. If you trace the signal path through the device it can be seen that the inductors and capacitor are in series. Now we have a Ground Tuning Unit (GTU) and can use binary selection of the inductances, together with rotating the variable capacitor, to determine the combination of inductance and capacitance for easiest tuning of the ground connection.

The inductances available on my L-match are 0.5, 1, 2, 4, 8 microhenries, allowing the inductance to be varied up to 15.5 microhenries in 0.5 microhenry increments. The variable capacitor is a 30-160pF polyvaricon.

Now, with the 8.67ft linear-loaded vertical erected and the “L-match GTU” making the ground connection via a capacitance plate on the ground, it was easy to select values that would allow smooth adjustment of the antenna SWR. It was found that 1 or 1.5 microhenries worked best. With these values selected the polyvaricon could be adjusted around mid-range to easily select best SWR.

A caution!

There’s a gotcha with this technique. My L-match has a switch to connect the top end of the variable capacitor to either the input or output. This is used to enable fast selection of either high or low impedance antennas. Referring to the diagram above, if the switch (not shown) is set to connect the variable capacitor to the left side of the inductors, this technique will not work. The inductors will be out of circuit and only the variable capacitor will be in circuit.

Will it still QSO?

My low-band QMX was dug out of its field pack and hooked up to the revised antenna (8.67ft of vertical window line with the “L-match GTU” providing the “other half” of the antenna. Using the “Tune SWR” feature of the QMX, the best SWR of 1.36:1 was obtained by a very small adjustment of the variable capacitor in the L-match GTU. Then it was time to go hunting. My best contact was in the state of Arizona (the “Arid Zone”?) almost 3000km away from my station in Southern Ontario. Signal reports were 599 each way. My sent report was a genuine 599 suggesting the antenna has good ears. The 599 report I received may have been genuine or perhaps it was just a “contest report”. In any event a good solid contact was made. A second contact into North Carolina only yielded a 549 signal report, but perhaps the low angle radiation pattern favored longer distance contacts.

Notice that the L-match GTU has no RF current meter. I could perhaps have inserted my home brewed RF current meter in circuit, but it wasn’t really necessary. Adjusting the ground current also regulates the radiating element current. Simply adjusting for lowest SWR indication on the radio peaks the radiated energy.

For practical outdoor use while hiking through the woods and rapidly deploying the antenna in clearings, the L-match GTU will be replaced with a much smaller series L-C coupler (2T2C). A 13ft Crappie pole is used to support the antenna. It collapses to the perfect length for carrying inside a fishing pole bag (no surprise there then) and is very lightweight.

There’s another gotcha

When the current distribution on the antenna was viewed in EZNEC it was discovered that the current maximum is in the ground circuit instead of in the radiator. Just like any ground-mounted antenna, this can lead to ground losses and inefficiency. However, the primary design objective was not to seek a Nobel Prize in antenna physics, but to come up with a design that meets the objective of a rapid deployment, simple antenna for hiking through the woods. The Linear-Loaded Monopole may just meet that requirement, but I have other ideas to try first. Stay tuned.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Amazon reveals aviation antenna as LEO inflight connectivity race intensifies

https://fed.brid.gy/r/https://spacenews.com/amazon-reveals-aviation-antenna-as-leo-inflight-connectivity-race-intensifies/

The “tootie-toosie” and the Hiking Antenna

My favorite way of operating is to hike into the woods, find a clearing, set up a quick and easy antenna, make one or more contacts and move on. Well, to be honest, I might pause long enough at a back country waypoint to get out my Aeropress and brew up a refreshing cup of Joe.

To do this my antenna must be simple, compact, lightweight and (hopefully) efficient. The simplest arrangement that meets those criteria is an end-fed wire, but quite often the trees are not tall enough, or contain dense brush in which wires can become entangled. I needed something compact and self-contained that is easy to carry into and set up in a dense wooded area.

I came up with a couple of ideas. First up to bat was a Linear-Loaded Monopole (LLM: no, not a Lunar Landing Module). The LLM is a recent bizarre invention that escaped from my basement skunk works lab and made its virgin QSO in the outback (out in my backyard). But I also had another idea on deck – a converted photo lighting tripod with short whip that I used very successfully out in the field last summer.

Other craft ale inspired ideas may enter the fray during the course of the coming weeks and months but, for now, let’s discuss these two strange RF launch systems.

A rapid deployment hiking antenna does not share the same design imperatives as other less temporary antennas. The efficiency – the proportion of energy radiated compared to the amount delivered to the antenna by the transceiver – is obviously important, especially since my transient operating base will be primarily QRP. Rapid deployment is the key objective; it must be very fast to set up and tear down. Hiking expeditions often take me well away from my vehicle and any road. I operate in areas that are heavily forested and patrolled by sometimes aggressive black-coated guardians with big teeth and long sharp claws.

Another requirement that factors into the design is a small ground footprint. Trails in these parts are often shrinkingly narrow, rocky, uneven and sometimes covered in mud or pools of rainwater. Laying out a system of radials on the ground is not an attractive proposition and sometimes it is next to impossible. In a recent post (Link: Be gone pesky radials!) we introduced an alternative using a Ground Tuning Unit (GTU). Well, that’s all fine and dandy but the GTU I had built is a a little big and heavy for carrying down a trail. I challenged myself to come up with an alternative.

Most of my outdoor operating time is spent on one band: 20 meters, so I wondered whether it would be possible to design and build a much simplified alternative to the GTU that would be very small, very light and serve the same purpose. I came up with something that met those criteria very well indeed.

Enter the “tooty-toosie”

The “tootie-toosie”, or 2T2C is a Tuned Tank Circuit Coupler. The idea involves a tank circuit designed to resonate at a desired frequency. The frequency I targeted was 14.060 MHz which is the CW calling frequency in the 20-meter band. This L-C circuit is actually a series connected resonator so maybe not strictly a “tank” circuit but I liked the “tootie-toosie” name anyway.

It is actually quite difficult to wind an inductor and select a capacitance for resonance on a specific frequency. Instead I targeted the bottom end of 20m (I am a CW op). Component tolerances limit the accuracy so I gave it my best shot and the end result was quite good. A simple L-C resonant circuit will have a fairly low Q and that will give some leeway in the frequency response. I measured the finished project on a nanoVNA and the peak in the curve showed a useful bandwidth at the bottom end of 20m.

I had already designed a great little tool to assist in a project like this. It is a LibreOffice Calc spreadsheet that will compute the resonant frequency of an L-C tank circuit, or the capacitance required with a known inductance to resonate at a desired frequency; or the inductance required with a known capacitance to resonate at a desired frequency.

I plugged in some parameters to come up with component values needed then began construction.

Just like with previous projects I didn’t have the correct toroidal cores in my component drawer. And just like with those previous projects I leaned on my inner MacGyver to find a solution. T37-2 powdered iron cores were the best I could find and, just like before, I stacked multiple cores together to make a bigger aggregate core. As I understand it, inductors wound on toroidal cores perform best when as much of the winding as possible lies within the core. That gave me an idea. If I built a MacGyver version of a binocular core most of the winding will be inside the core. Could that work?

Here is how it came together. Two tightly stacked sets of three T37-2 powdered iron cores were put together and secured with electrical tape. Then thin enameled copper wire was wound through the cores until the cores were full of wire. [By the way, the enameled copper wire was scrounged by unwinding old surplus transformers I had in my junque drawer]. I had no idea whether this would work but I gave it a try anyway. The inductance measured on my L, C meter was 29 microhenries.

The tuned circuit calculator told me that was probably too much inductance, but it would be easy to reduce it by unwinding a few turns of wire. I wanted to use a 10pF ceramic capacitor (I have hundreds of them) so I needed only about 13 microhenries in the inductor.

After carefully unwinding the cores and measuring the inductance I got it down very close to 13 microhenries. The capacitor and inductor were quickly soldered together in series to create my tuned circuit.

About that capacitor

A tiny ceramic disc capacitor looks a little dodgy in this application. It has to carry the full AC current flowing in the ground circuit of whichever hiking antenna is chosen. Operating QRP puts less stress on the capacitor so I am hoping it can carry the load. As a backup a short length of thin speaker wire, or maybe even coax can be substituted in place of the ceramic capacitor.

[UPDATE: the ceramic capacitor has now been replaced with a compression trimmer. The only value I had available is 3-30pF so I reduced the number of turns on the coil so that the trimmer could be adjusted near its top end. Adjustment is quite coarse but it gives some flexibility to peak the ground current fairly accurately.]

First field test

Most of the winter snow that was in my backyard has now melted so I was able to set up the tripod/whip antenna shown in the picture at the top of this post. Last summer this antenna was used with either two raised radials, or four ground radials. Will it work with the 2T2C ground coupler? On the day of the test there was a major solar storm and the bands were silent, but at least it would still be possible to see if the antenna would tune up with the radials replaced by this new arrangement.

This antenna has a radiating element only 13ft long made up of a 9ft Buddipole whip with the remainder coming from the tripod main tube itself. It requires a 4:1 unun and a tuner but has the advantage of operating on multiple bands from 20m up to 10m (but used as a fixed 20m antenna in this experiment).

The test was successful in demonstrating that the antenna with this new fixed, tuned ground system would deliver a low SWR (1.3:1) to keep the transceiver happy. The next step, when the bands cooperate, is a full magic smoke test.

Ham Radio Outside the Box will report back when the hiking antenna options have been exposed to full field conditions. I am looking forward to getting back into the woods with my radio gear after another long, snowy winter!

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Isn’t every quarter-wave antenna really a half-wave antenna?

It’s a bit early for April Fool’s jokes so this is a perfectly serious discussion. Just maybe, the distinction between a quarter-wave and a half-wave antenna is a bit more obscure than we thought. Which is better; a quarter-wave or a half-wave antenna? Does it even matter if indeed every quarter-wave antenna really is a half-wave antenna? The answer is not straightforward and we will explore why in this week’s post.

Let’s all use our noddles

An expert could be defined as somebody who knows at least a little more about a subject than most other people. I am not an expert, but I do have a very inquiring mind. Don’t accept anything you read here without question. Science is the process of submitting a hypothesis which can be challenged, refuted, updated or even discarded. New hypotheses can replace old ones as further studies are completed. Treat everything you read here as a hypothesis; it might be completely wrong, partially right or even brilliantly correct. Challenge it with your own critical thought because I thought I was wrong once – but I was mistaken 😉

How to improve the efficiency of an antenna by burying half of it in the ground

Sounds ridiculous doesn’t it? But isn’t that exactly what we do when we erect a ground-mounted quarter-wave whip with a set of radials? What role do the radials play? Do they reflect the signal away from the ground? “Experts” say no, so my hypothesis suggests that an efficient set of radials establishes a ground plane that is better (or worse) than the actual ground itself.

The Good Earth

The problem with “the good Earth” is that it isn’t always. It depends on the conductivity of whatever our antenna is mounted on. Seawater could be considered the best ground plane but it has an unfortunate habit of being a slightly unreliable support for antennas. Moving inland a little we have sand, nice firm sand. The sea is still close by and helps with antenna efficiency and directionality, that is if you wish to send your signal in the direction of where the sea is.

Unfortunately for me, the closest sea (James Bay in the near Arctic) is over a thousand kilometers to the north and is frozen for much of the year. So I have to rely on the conductivity of the soil in my area. I live in the Great Lakes region and I am surrounded on three sides by the waters of mighty Lake Huron. Pure freshwater is almost a perfect insulator, but I have the advantage of living on the Niagara Escarpment and water from my well contains over 2000 parts per million of dissolved solids. That may improve my soil conductivity for ham radio purposes but it cost me a small fortune in water treatment equipment to get rid of those dissolved solids to make the water drinkable.

Whenever I wish to deploy a ground-mounted antenna I have to rely on ground radials because sometimes my portable operations take me to locations where I set up on the ancient bedrock of the Canadian Shield, or sandy lakeside beaches where the ground conductivity is not so good.

How do ground radials really work?

I hypothesized earlier that radials establish a ground plane. Their purpose is to give the antenna – and it’s image in the ground – a zero reference point. If this ground plane is efficient (i.e. lots of radials) the current in both the ground and the antenna will increase. Higher current in the antenna means more signal is radiated. And what about that higher current in the ground? The earthworms will thank you for the extra warmth.

By the way, counterpoise or radials?

The two terms are often confused. When I use the term “counterpoise” I use it to mean “the other half of the antenna” which may be made up of a set of radial wires, or a blanket of Faraday cloth, or AA1AR, Bruce’s copper mesh.

What’s to be done?

If half our signal is warming the winter nightcrawlers what can we do to redirect the crown joules in a more useful direction? First, let’s examine the current distribution in a half-wave antenna wire.

Let’s call it a “voltage-fed” antenna because a lot of half-wave antennas are end-fed. It could equally be a center-fed dipole which is also a half wavelength long. There are several different ways to erect an End-Fed Half-Wave antenna:

• Vertical
• Flat top
• Inverted-V
• Inverted-L
• Sloper

Notice that however we erect it, the entire antenna remains above ground. Some online advice suggests the ends of the wire can be placed close to the ground because there is almost no current there. Others disagree and note that the ends of a half-wave wire are high voltage points and should be kept above head height. And it isn’t just for safety reasons. What are the effects of placing a high voltage point close to ground? Could there be some ground interaction that affects the antenna performance. Any experts care to comment?

Enter the Dipole

A dipole or an EFHW can be erected vertically. Let’s talk about the dipole. It is a center-fed half-wave (a CFHW if you like acronyms). A vertical dipole could be described as a quarter-wave vertical antenna with a quarter-wave counterpoise. Can’t see it? Suppose the counterpoise section is tilted away from vertical. Now it looks more like quarter-wave with a counterpoise. But, the whole antenna is still a half-wave, isn’t it?

Bifurcate that counterpoise

A bifurcated counterpoise is a fancy way of saying split it in two, or in other words, duplicate it. Why? Well again, this is my personal theory. The lower half of a vertical dipole may come close to ground unless it is raised high enough. Ground effects may distort the radiation pattern. If we add an extra wire to the counterpoise section the antenna looks like an Inverted-Y and the current in the counterpoise is split between two conductors. If the current in each conductor is half that of a single conductor the resistive loss in the counterpoise section will be lower, and any ground interaction may be mitigated.

I have occasionally used an Inverted-Y for many years. It was one of the earliest antennas I ever built and performs well. An Inverted-Y built for 20m has to be erected at a height of at least 30 feet (~10m). At that height the feedpoint sits about 13ft above ground and the two radials must be spread at quite a wide angle to remain clear of the ground. I wonder whether we could make this antenna more stealthy? A 30ft mast in a busy public place tempts unwelcome attention from passers-by and park officials. Some ideas rattling around in my old, grey noddle are:

• Lower the apex by shortening the radiating element with a low-loss capacitance hat at the apex
• Reduce the length of the radiating element AND the radial wires using linear loading (folding the wires back on themselves with a small spacing)

Any other ideas from readers would be most welcome. Let me know what you think in the comments.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

A short and maybe not-so-sweet HF antenna

A lot of information has been posted online recently about very short portable vertical antennas. There must be some magic in how they work, surely, since they appear to disobey the laws of physics. I used to own one called a “Miracle Antenna”; it was manufactured in Quebec, Canada. It comprised a 57-inch telescoping whip mounted on a remarkably well-engineered toroidal loading coil with many taps selectable by means of a rotary switch. The Miracle Antenna could be used from 80m up to 70cm with a suitable counterpoise. The loading coil switch had a bypass position so that the antenna could be used as an unloaded whip for VHF/UHF. The 57-inch (~1.5m) whip is a three-quarter wavelength on 2m; 70cm could be selected by shortening the whip.

I made lots of contacts!

I was thoroughly impressed by my Miracle Whip; I made lots of contacts with it. Really; it worked remarkably well – but only on VHF. Perhaps if I had tried harder with it I could have snagged some QSOs on HF too, but that never happened. It was relegated to the role of a great 2m band antenna used for accessing my local repeater.

So what’s up with very short antennas?

First, let me dispel one myth about them. With a suitable transmatch (tuner) or adjustable loading coil, a nice low SWR can be obtained even from the shortest of shorties. Let’s say you can tune for 1:1 SWR on multiple bands. Great! Now key up and start working the pile-ups! Yes? Or no?

Whoa … Not so fast pilgrim!

The SWR that the radio sees results from a private negotiation between the transmatch and the radio; the antenna doesn’t enter into it. Compare it to a wild west cowboy town. The local sheriff maintains law and order inside the town, but outside the town it’s still the untamed wild west.

The SWR at the feedpoint of a very short vertical antenna (excluding loading coil) is very high. That high SWR is presented to the “tuner” as a high impedance that the “tuner” transforms to 50 ohms resistive, or close to that value. That “varmint” of a shortie antenna remains a wild, untamed, high SWR beastie. Why is that?

There is another factor to consider and it is critically important. It’s called Radiation Resistance (Rrad). Rrad is a strange animal in that a high Rrad results in higher efficiency of the antenna. Very short antennas have a very low Rrad. I set up a 57-inch whip on a tripod and attached a 17ft counterpoise, them measured the Resistance and Reactance on the 20m band. The numbers I obtained were 1.98 – j53 ohms. The reactance value (X = -j53) was actually a lot better than I expected and I have a theory about why that is. I will explain later in this post.

Now let’s look at how antenna efficiency is calculated. An antenna has two types of resistance; Radiation Resistance (which is good) and Loss Resistance (Rloss which is bad, very, very bad). Loss resistance includes every connection between components in the antenna system, ohmic loss in any loading coils as well as ground loss in the counterpoise system. Efficiency is the ratio between Radiation Resistance and total resistance:

Efficiency = Rrad/(Rrad+Rloss)

Lets assume the Rrad value is equal to the real component of the antenna’s impedance; in the example given above that’s 1.98 (let’s call it 2) ohms. Determining the value of the total loss resistance is not easy. There will be a few ohms of resistance in all the connection points and definitely in the loading coil – especially for a base-loaded vertical since the current is at a maximum at the antenna feedpoint. But the biggest losses may come in the ground system.

Typically, from accounts I have read, operators often lay just a single counterpoise wire on the ground. The current in this wire will be the same as the current in the radiating element and will be almost totally lost in the ground.

Now, let’s look at how my experimental shortie vertical antenna would perform if I took it out to the field. And, also, let’s assume I used a base loading coil to resonate it instead of a tuner. If I adjusted the coil to give a 1:1 SWR guess what? That would be VERY BAD, VERY VERY BAD. Here is why:

We can insert the value I measured for Rrad into the efficiency formula given above:

Efficiency = Rrad/(Rrad+Rloss) – inserting measured value of Rrad: Efficiency = 2/(2+Rlos).

Since we have also measured an SWR of 1:1 the feedpoint impedance is 50 ohms (resistive) comprising the total of Rrad + Rloss.

Now we can deduce the value of Rloss as the difference between the 50 ohm resistive impedance at the feedpoint minus Rrad. Rloss = 50 – 2 = 48 ohms.

So the efficiency of our shortie antenna can be calculated as 2/50 = 4%.

Gadzooks!!!

If little shortie is used with a QRP radio putting out 5 watts into the antenna, the actual radiated power will be only 4% of 5 watts = 200 milliwatts. That’s sad.

Hey Jude, don’t make it bad

“Take a sad antenna and make it better”. There are two ways to make an antenna better. We can increase its radiation resistance or reduce its loss resistance. The first way is very easy; the second is more difficult. To increase its radiation resistance all we have to do is make it longer. We know that a half wave antenna has an endpoint impedance that is resistive and very high – typically 2000 ohms or more. If we plug that into the equation we get an efficiency of 2000/2000+48 = 98%.

“What a load of horse feathers, I still make plenty of contacts with my short vertical”

Yes, of course your 200 milliwatts will still be heard and you will still make contacts. Let’s introduce another bit of physics to explain why. It’s called the Inverse Square Law. It states that the strength of your signal is proportional to the square of the distance between the transmitting station and the receiving station. Modern HF receivers are very sensitive and can receive signals down into the microvolt range. If the receiving station has “big ears”, i.e. a big efficient antenna, it has a better chance of picking up very weak signals and will hear your 200mW signal. But at a certain distance the Inverse Square Law dictates that the strength of your signal will have fallen below the threshold at which even Big Ears can detect you. But, the Inverse Square Law applied to stations closer to you means your 200mW will still be heard.

If the DX can hear you, can he still work you?

Now let’s look at another situation in which Big Ears can hear you fine business and replies to your call. Now yet another bit of physics comes into play – it’s called the Reciprocity Principle. Simply put it states that an antenna’s transmit efficiency is the same as its receive efficiency. So Big Ears is calling you but you may not be able to hear him.

There’s no free lunch

There are lots of shortie antennas available. If you choose to build, or buy one you will have to accept that, while you may have fun with it, it has limitations. When propagation is good you may even get some pleasant surprises.

Oh, I see, that’s why …

Finally, I wrote earlier in this post that I was surprised at the relatively low capacitive reactance of the shortie antenna I put up for testing. I think I can explain why. At my home QTH in southern Ontario, Canada, winter hasn’t finished its dastardly doings yet. It was way too cold and windy outside to venture out onto the planet’s surface for antenna experiments, so I set up my 57-inch whip on a tripod inside the house and laid 17 feet of wire across the floor as a counterpoise. It is possible that this appeared as an ungrounded Off Center Fed antenna to my RigExpert antenna analyzer. The total length was just under 22 feet which is about 2/3 of a half wavelength on 20m. The analyzer might then have perceived this as a less inefficient antenna than a short vertical (0.075 wavelengths on 20m) worked against an electrical ground.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#UK Peeps. Take a minute and sign and share with your fellow hams.

#England #Mast #Antennas #Petition

In reality it's probably asking too much....but bless them for trying.

https://petition.parliament.uk/petitions/755675

#UK Peeps. Take a minute and sign and share with your fellow hams.

#England #Mast #Antennas #Petition

In reality it's probably asking too much....but bless them for trying.

https://petition.parliament.uk/petitions/755675

#hamchallenge week 3: Understand how your antenna works. 🧵

Let's check out the lowband vertical antenna I built before #CQWW in November. It is 16.5m long, built with an 18m Spiderbeam mast minus the top element. About 18m of wire are coiled up on it (for stability), and it is tuned at the feed point with a CG3000 automatic tuner. There are 12 ground radials with an average length of 10m below it. When I built it and laid out the radials, I noticed that the feed point impedance stayed at about 37 Ohm at the resonant frequency of ~ 4.1 MHz any more after 12 radials, so I left it like that. HC03 @hamchallenge #hamradio #antennas

1/4

Woo! The MyAntennas 7510-1K EFHW antenna got here! I'm so excited, and am just waiting for some coax to get here so I can mount and get it all set up! It feels so high quality, so I'm really looking forward to seeing how it performs. I'll finally be able to get on something other than 10m, 12m or 6m! YAY!

#hamRadio #hamShack #antennas #hf #efhw

Ich teste auf @[email protected] Empfehlung gerade #sharkey auf procial.tchncs.de. So weit so schick. Jetzt versuche ich über #antennas zahlreichen Hashtags zu folgen, aber ab der 6. #antenne kriege ich eine Fehlermeldung, dass ich das Erstellugslimit erreicht habe. Ist das eine Limitierung von Sharkey oder vom Server oder übersehe ich was? Max 5 Antennen scheint mir arg wenig. #fedihelp

So, I've done it. I ordered an EFHW antenna from myantennas.com, which covers 75m-10m! I still have to pick up a few other things to make it all connect in to my shack, but I will finally be able to get on other bands soon! Now to just hope for a good enough day to get on the roof and hook up coax and lightning blocks and get everything all mounted. I'm so excited!

#antennas #hf #efhw #amateurRadio #hamRadio #hamShack

I wonder if it makes sense to approach job search through hobbies and side activities rather than just by past employment history.

In my free time, I do #microbiology. I have a #biolab in the cellar with petri dishes and microscopes and all. I ferment #olives which grow in my tree and make pickles out of them, I make two kinds of #sourdough bread from a culture I extracted from quince fruit peels from my own tree, one wheat and one #rye.

I do #mycology. I have some 2,000 photos of wild #mushrooms in my Facebook photo albums.

I do a lot of software-defined radio, I have more #antennas than I care to count, and also more #SDR modules than I care to count. I stream radio data directly to my own #ElasticSearch which I can visualize in different ways in Kibana.

I do home automation, and the house has countless sensors and cameras. I use #HomeAssistant for this, with lots of modules I have implemented myself, for example for scraping data from my Huawei solar panels and graphing their historical data.

I have a home #Kubernetes cluster with many nodes and several public-facing services with some 99.9% uptime like a local Mastodon instance and also a #Matrix instance, in addition to lots of local services.

I am a data archivist and I have lots of stuff backed up locally if the internet goes down like it did during the notorious #apagon in Spain.

I play strategy games in Playstation, some of my current favorite games are #Stellaris and #Tropico6. I just like resource optimization over time.

I grow vegetables and some fruit trees. Trying to get really hot chilis growing here as they aren't readily available in stores. I have eaten the One Chip Challenge without even wincing a bit. I am a #ChiliHead.

I administrate all sorts of online communities and web pages. I read a lot of books and whenever I get into a new domain, I tend to read several definitive reference books of the topic from cover to cover. For example I now know more about #cancer biology than I ever thought I would.

I used to take a lot of #Coursera courses, also in non-technical topics such as #virology, #BrainPhysiology, #AnimalBehavior and such.

We have 3 cats, 2 siamese and 1 rescued as a kitten from the neighboring empty plot where he was born.

Ask me anything about these things!

If you need someone like this in your team to build great things, working remotely from Spain, let's chat!

#AI #AGI #OpenToWork #RemoteWorking #FediHire

A handy little site if you need a bespoke ¼λ ground plane antenna. Stumbled on this whilst trying to find a design for a simple 477MHz antenna for UHF CB use. The calculator lets you adjust for whatever frequency you need.

https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/

#AmateurRadio #CBRadio #Homebrew #Antennas

What really determines the efficiency of an antenna?

Is it Standing Wave Ratio (SWR)?

It is common knowledge that when an antenna has high SWR some of our transmitted power is wasted instead of being transmitted. But is this really true? The trouble with “common knowledge” is that it spreads without further scrutiny. “It must be true because that’s what everybody thinks”. But let’s consider another perspective.

What happens to our signal when it meets an antenna with high SWR? Some of the signal is radiated while the rest is reflected back down the transmission line to its source – the transceiver. What happens to the reflected signal when it reaches the transceiver? It is re-reflected back towards the antenna and the cycle repeats.

So does all the signal eventually get radiated? No. Energy is lost (RED ALERT from the physics department: Energy can neither be created nor destroyed, only converted from one form to another). Ok, my apologies to the physics department, some of the energy is converted to heat as our signal passes along the transmission line and through any ununs, baluns, impedance transformers or other devices en route. Further energy is converted to heat due to the resistance of the wires and the impedance of the transmission line itself.

Thus, on every trip between the transceiver and the antenna, some of our transmitted RF is converted to heat. If the antenna has a high SWR some of our signal travels back and forth between the transceiver and the antenna multiple times and becomes further attenuated on each trip. Therefore, if we can reduce the loss of RF (due to conversion to heat) as it passes through any devices along the journey between the source (transceiver) and load (antenna) we will improve the efficiency of our antenna system.

How can we do that?

One simple way to achieve that is to correct for the high SWR right at the antenna. A remote tuner can do that. A loading coil will compensate for the high capacitive reactance of a short antenna, but loading coils can be inefficient because of wire resistance. This is especially true in the case of base-loading coils on a quarter-wave vertical antenna. The current is highest at the base of the antenna so more RF energy will be lost to heat (P=I^2*R) than with a center-loading or top-loading coil.

So the real culprit is not SWR, but the insertion loss of ununs, baluns, impedance transformers, loading coils, transmatches and any other “energy conversion” devices, including the transmission line itself, through which our signal has to pass.

Insertion loss of Ham Radio Outside the Box’s 4:1 ununs

In the previous post I reported on my build of field test versions of a 4:1 unun and a 4:1 balun to compare how each would handle the task assigned to them. Now the job I set myself was to transform what might be called the “Ugly Sisters” builds into something with the good looks of Cinderella. And Cinderella had to be an unun tough enough to withstand rough treatment out in the Big Blue Sky Shack through all four Canadian seasons (Late Winter, Brief Summer, Early Winter, Deep Winter).

I built two versions of a 4:1 unun; one for QRP and another for what I like to call QROp. “QROp” is an unofficial label I have adopted to mean about 20 watts or so. Twenty watts will give a 1 S-unit advantage over 5 watts – maybe just enough for our signal to poke its nose above the noise floor when propagation conditions are not so good.

There are 2 main differences between the QRP and the QROp versions: The QRP unun uses a BNC connector and a 4:1 transformer wound on a tiny FT82-43 toroid. The QROp version uses an SO-239 connector and a 4:1 transformer wound on an FT140-43 toroid.

If we look at the tables below, we can see that the QRP version may have a little too much insertion loss. When we are trying to do as much as we can with as little as possible every milliwatt is wanted. As the wonderful friendly folks on the big Canadian island of Newfoundland like to say: “A little’s a lot if it’s all you’ve got”.

Insertion Loss effects of the Ham Radio Outside the Box QRP unun

Insertion Loss effects of the Ham Radio Outside the Box QROp unun

A little extra heat in winter

You would think Canadians wouldn’t mind a little extra heat in winter. It’s true, but not when the source of that heat is our precious transmitted RF. In case you were wondering, the amount of RF converted to heat by inefficient devices is mostly undetectable. If it can be easily detected the “magic smoke” can’t be far behind. When it’s 253 Kelvins outside you just ain’t gonna notice when the temperature rises to 254 Kelvins (note: the physics department advised me to use Kelvins to avoid confusion between degrees Fahrenheit and degrees Celsius).

Oh no! There’s more?

Yes indeed. An unun does not attenuate Common Mode Current (CMC). For that we need a Common Mode Current Choke (CMCC). CMC is the current on the outer surface of a coax braid. Differential mode current is carried on the core and inner surface of the coax braid. Does a CMCC also have insertion loss? Yes, but how much? Let’s take a look.

Insertion Loss of a QRP (5 watts) Common Mode Current Choke (CMCC)

Insertion Loss of a QROp (20 watts) Common Mode Current Choke (CMCC)

The (not so) grand total of RF going up the chimney

The white bearded man in the red suit and his flying reindeer might be grateful for a few watts of heat going up the chimney at this time of year, but those of us in the frozen barren tundra of the northern states and provinces, as well as licensed ham dwellers in other cold lands, may not see things the same way.

What can we conclude?

If we only consider the insertion loss – in this example – of the 4:1 voltage unun and the Common Mode Current Choke and ignore resistive losses in the transmission line, and possibly insertion loss in a transmatch (“tuner”), we can determine the potential efficiency of our antenna system.

• For our QRP devices the efficiency varies between 81.6% and 90% across the bands
• For our QRO devices the efficiency varies between 90.9% and 93.5% across the bands

This conclusion is based on the assumption that there is no loss in the antenna itself. We are treating the antenna, the transmission line, unun and CMCC as the “antenna system”. I have made no allowance for SWR losses for the reasons stated in the introduction to this post.

What a load of old codswallop!

I am an expert in the sense that “X” is an unknown quantity and “spurt” is a drip under pressure. I may be completely wrong; I may have fallen off my horse and bumped my head on a rock. I may have come to a fork in the road and taken it as Yogi Berra once famously said. If you would like to correct me on any wrong assumptions please do so. I receive a lot of direct emails from readers and, while they are most welcome, if you write a comment to this post instead it may trigger an interesting technical discussion here.

A big thank you to all the new and many existing subscribers to Ham Radio Outside the Box. It is people like you who make writing these posts so worthwhile. I appreciate every one of you.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#amateurRadio2 #antennas #cw #outdoorOps #unun

POTA PERformer radials – can we make a compromise?

There has only been one light snowfall in southern Ontario so far this season – just a few centimeters that melted away within a couple of days. In anticipation of upcoming heavier snowfalls and a semi-permanent white blanket that will last until spring, I bravely shrugged off the chilly outside air and set up my Ham Radio Outside the Box version of the POTA PERformer antenna out in the backyard to experiment with radial lengths.

The cunningly repaired broken shortened whip with a capacitive top hat, to compensate for its inductive reactance on the 20m band, sat atop my custom spike mount that, despite falling temperatures, could still be pushed into the ground about 25cm (10 inches). Two radials were attached each of which sloped down to a fiberglass stake about a foot (30cm) above ground. The radials are approximately 5m (17ft) long for the 20m band with links to shorten the wires for the 17m and 15m bands.

Now, to find a shortcut

The objective for the day’s tests was to investigate whether compromises could be made in the radial lengths. Why? Later in the winter, when the snow lies deep and crisp and even, it can become a real chore to wade through accumulations of the infernal white stuff to adjust the radial lengths for band changes. I have adopted 2mm banana plugs for the links – a great idea in the summer, but maybe I neglected to consider what will happen when even a few snow flakes freeze on those tiny connectors in the winter!

So, how to minimize pedestrian excursions through the challenges of winter operating conditions to accommodate band changes? The POTA PERformer is an efficient antenna but it was designed in California where the climate is just a little milder than in Ontario. Should I go back to using a random wire antenna – like the Rybakov – until spring comes around again?

I could perhaps use “fan radials” i.e. separate radials for each band. That would probably work but setting them up might still involve wading through deep snow. In the past I have used ground radials laid on the snow – a multiband arrangement that requires no adjustment for band changes, but is less efficient.

Back to the backyard tests; what did I find out?

• First, my approximately 16.5ft (~5m) raised radial wires provided an acceptable SWR (less than 2:1) on 20m and 17m (with the whip length shortened for 17m).
• Second, the same wires – with the links adjusted for 15m and the whip shortened again – gave an acceptable SWR on 15m, 12m and 10m.

So, is this a result? Maybe not. There is a potential for lost efficiency when the radiating element is shorter than the counterpoise. Let me explain.

Let’s assume we are using a field portable version of the POTA PERformer in which the feedpoint remains quite close to the ground – maybe 1 to 1.5 meters. The two radial wires slope away from the feedpoint to an end point even lower to the ground. Now, if we examine the current distribution on a halfwave dipole, we can see that the maximum current, and therefore the point at which maximum RF is radiated, is located in the center of the dipole.

We would like the high current point to lie within the radiating element, not the counterpoise. For the purposes of this discussion we are going to refer to the two radial wires as “the counterpoise”.

Going back to my backyard tests, I found that:

• a 20m counterpoise “worked” on the 17m band.

• a 15m counterpoise also “worked” on the 12m and 10m bands.

In each of these cases the radiating element was shorter than the counterpoise.

Referring to the accompanying diagrams we can see that the high current point, in each case, lies within the counterpoise.

Does this finding matter?

Changing the radiating element versus counterpoise balance creates an antenna that looks very much like an Off Center Fed Dipole (OCFD).

If an OCFD is mounted high enough above ground it doesn’t matter at all although two things need to be considered here:

1. Changing the radiating element versus counterpoise lengths changes the impedance at the feedpoint.
2. The overall length of the dipole might change unexpectedly. This can be seen with Greg KJ6ER’s Challenger antenna which is a vertical OCFD halfwave dipole that is shortened by laying part of the counterpoise wire on the ground.

A relatively small change in the ratio between the radiating element versus counterpoise lengths changes the feedpoint impedance, but this can be compensated by adjusting the whip length to still obtain a usable SWR.

However, we cannot compensate for the proximity to ground of the counterpoise in the POTA PERformer. If the current maximum occurs at the feedpoint (1 to 1.5 meters above ground) very little power is lost. But, if the current maximum occurs below the feedpoint we are going to keep the earthworms warm in winter.

Not the best plan

So we can conclude that using a 20m counterpoise on 17m risks losing some of our RF energy to the ground. The same applies for using a 15m counterpoise on 12m and 10m. The following diagram summarizes this.

The way forward

“Fan radials” may still be a solution but they require some careful experimentation. There is interaction between the wires for each band due to mutual capacitance. This is compounded when multiple bands are involved. To make matters worse, when used out in the Big Blue Sky Shack where the wind doth blow through the wires and changes the interaction, who knows what wild swings in SWR may occur? The radio I have dubbed my “very clever poodle” (QMX: see last post) will not take kindly to that.

A final thought

I have watched several videos in which a very short whip is mounted on a picnic table and used with a single long counterpoise wire draped down to and across the ground. Sometimes the “Magic (Tune) Button” assists in finding an SWR that keeps the radio smiling. Contacts get made, so what’s the problem? I hope the above discussion answers that question.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#amateurRadio2 #antennas #counterpoise #ground #outdoorOps #pota #qmx

POTA PERformer radials – can we make a compromise?

There has only been one light snowfall in southern Ontario so far this season – just a few centimeters that melted away within a couple of days. In anticipation of upcoming heavier snowfalls and a semi-permanent white blanket that will last until spring, I bravely shrugged off the chilly outside air and set up my Ham Radio Outside the Box version of the POTA PERformer antenna out in the backyard to experiment with radial lengths.

The cunningly repaired broken shortened whip with a capacitive top hat, to compensate for its inductive reactance on the 20m band, sat atop my custom spike mount that, despite falling temperatures, could still be pushed into the ground about 25cm (10 inches). Two radials were attached each of which sloped down to a fiberglass stake about a foot (30cm) above ground. The radials are approximately 5m (17ft) long for the 20m band with links to shorten the wires for the 17m and 15m bands.

Now, to find a shortcut

The objective for the day’s tests was to investigate whether compromises could be made in the radial lengths. Why? Later in the winter, when the snow lies deep and crisp and even, it can become a real chore to wade through accumulations of the infernal white stuff to adjust the radial lengths for band changes. I have adopted 2mm banana plugs for the links – a great idea in the summer, but maybe I neglected to consider what will happen when even a few snow flakes freeze on those tiny connectors in the winter!

So, how to minimize pedestrian excursions through the challenges of winter operating conditions to accommodate band changes? The POTA PERformer is an efficient antenna but it was designed in California where the climate is just a little milder than in Ontario. Should I go back to using a random wire antenna – like the Rybakov – until spring comes around again?

I could perhaps use “fan radials” i.e. separate radials for each band. That would probably work but setting them up might still involve wading through deep snow. In the past I have used ground radials laid on the snow – a multiband arrangement that requires no adjustment for band changes, but is less efficient.

Back to the backyard tests; what did I find out?

• First, my approximately 16.5ft (~5m) raised radial wires provided an acceptable SWR (less than 2:1) on 20m and 17m (with the whip length shortened for 17m).
• Second, the same wires – with the links adjusted for 15m and the whip shortened again – gave an acceptable SWR on 15m, 12m and 10m.

So, is this a result? Maybe not. There is a potential for lost efficiency when the radiating element is shorter than the counterpoise. Let me explain.

Let’s assume we are using a field portable version of the POTA PERformer in which the feedpoint remains quite close to the ground – maybe 1 to 1.5 meters. The two radial wires slope away from the feedpoint to an end point even lower to the ground. Now, if we examine the current distribution on a halfwave dipole, we can see that the maximum current, and therefore the point at which maximum RF is radiated, is located in the center of the dipole.

We would like the high current point to lie within the radiating element, not the counterpoise. For the purposes of this discussion we are going to refer to the two radial wires as “the counterpoise”.

Going back to my backyard tests, I found that:

• a 20m counterpoise “worked” on the 17m band.

• a 15m counterpoise also “worked” on the 12m and 10m bands.

In each of these cases the radiating element was shorter than the counterpoise.

Referring to the accompanying diagrams we can see that the high current point, in each case, lies within the counterpoise.

Does this finding matter?

Changing the radiating element versus counterpoise balance creates an antenna that looks very much like an Off Center Fed Dipole (OCFD).

If an OCFD is mounted high enough above ground it doesn’t matter at all although two things need to be considered here:

1. Changing the radiating element versus counterpoise lengths changes the impedance at the feedpoint.
2. The overall length of the dipole might change unexpectedly. This can be seen with Greg KJ6ER’s Challenger antenna which is a vertical OCFD halfwave dipole that is shortened by laying part of the counterpoise wire on the ground.

A relatively small change in the ratio between the radiating element versus counterpoise lengths changes the feedpoint impedance, but this can be compensated by adjusting the whip length to still obtain a usable SWR.

However, we cannot compensate for the proximity to ground of the counterpoise in the POTA PERformer. If the current maximum occurs at the feedpoint (1 to 1.5 meters above ground) very little power is lost. But, if the current maximum occurs below the feedpoint we are going to keep the earthworms warm in winter.

Not the best plan

So we can conclude that using a 20m counterpoise on 17m risks losing some of our RF energy to the ground. The same applies for using a 15m counterpoise on 12m and 10m. The following diagram summarizes this.

The way forward

“Fan radials” may still be a solution but they require some careful experimentation. There is interaction between the wires for each band due to mutual capacitance. This is compounded when multiple bands are involved. To make matters worse, when used out in the Big Blue Sky Shack where the wind doth blow through the wires and changes the interaction, who knows what wild swings in SWR may occur? The radio I have dubbed my “very clever poodle” (QMX: see last post) will not take kindly to that.

A final thought

I have watched several videos in which a very short whip is mounted on a picnic table and used with a single long counterpoise wire draped down to and across the ground. Sometimes the “Magic (Tune) Button” assists in finding an SWR that keeps the radio smiling. Contacts get made, so what’s the problem? I hope the above discussion answers that question.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#amateurRadio2 #antennas #counterpoise #ground #outdoorOps #pota #qmx

QRP? Are we out of our minds?

If we believe in QRP – I mean really, really believe – then we can make it work. Admittedly it’s like betting on a race between a tortoise and a hare; where would you put your money? If you read accounts written by diehard QRPers, do you ever see stories such as: “I went to the park with my latest QRP rig today and called CQ for five hours but only got 2 QSOs. On the way home I tossed that stupid rig in the river and bought a big-boy radio instead”? Of course not. Diehards enjoy the outing as much as the contacts. They get a thrill out of tickling the ionosphere even if the big bad D-layer swallows their RF and has a malignant chuckle to itself.

I am not a diehard, but I do like to operate QRP whenever it yields a good probability of actually getting contacts. On the other hand, when propagation conditions are unfavorable, or I cannot erect an efficient antenna, I am willing to switch to warp power to get the job done.

The FCC has given us guidance in the form of the Part 97 rules, and to paraphrase them:

“Use (only) as much power as in necessary to make the contact”

There are different ways to interpret that guidance. For many QRO operators it means “fire up the amp and let ‘er rip; life’s too short …”. The word “only” in the above may occasionally fall on deaf ears. QRPers, on the other hand, might see things differently and ask: “How can we make this work without increasing power?”.

There are days when 5 watts into a tiny coil-loaded whip is all you need; for other days there are tricks that can be employed to make a teeny-weeny smidgen of RF create the illusion of a really big-boy signal. The big secret is that it doesn’t matter how much signal the P.A. of our radios – big, small or tiny – presents at the antenna jack. What really counts is how much signal appears at the receiving end.

A military ELF (Extremely Low Frequency) radio station puts out a huge amount of power, but the amount reaching a submarine somewhere beneath the world’s oceans is only a few watts – effectively QRP. QRO operators can emulate that idea by using a dummy load with a random wire antenna attached. No tuner needed, any old antenna will work and the radio will always see a low SWR. It is said to work just fine but with the caveat that you will lose about 1 S-unit in signal strength due to loss in the dummy load. Would it be possible to invert that situation and transmit a very low power signal that a receiving station would perceive to be more powerful?

Don’t announce your handicap

If we call CQ and identify ourselves as QRP we are telling the world we are transmitting a teeny-weeny smidgen of a signal and that negatively influences the receiving station’s perception. In his book “Winning through intimidation” author Robert Ringer tells of clever benevolent techniques he employed in his sales career to dazzle potential clients into having a glowing perception of him. So let’s not mention our piddling power and allow the receiving station to assume we are just another regular ham station, or maybe even a superstation.

Use an efficient antenna

When conditions are right you can make contacts with a wet noodle. In most cases it makes sense to assume conditions are unfavorable and plan for the worst. That means putting up an efficient antenna – one that converts as much of our feeble signal as possible into radiated RF. If we can put up a gain antenna, even 3dB of gain, we will double our effective radiated power.

Don’t use a vertical antenna

Well, ok if we have to use a vertical antenna it should be raised off the ground. A ground mounted vertical antenna requires a lot of radials to be efficient. If it is raised as little as 1 meter above ground less radials will be required – maybe as few as 2.

A vertical antenna radiates equally in every direction so our feeble signal is spread around 360 degrees. If that signal can be focused to favor a specific direction, the receiving station will perceive it to be stronger. Greg KJ6ER’s POTA PERformer can effectively focus a signal even more than he intended by sloping the radiator away from the direction we wish our signal to go. Modeling with EZNEC shows a front/back ratio of over 8dB can be obtained by this method. That means more of our signal is being directed towards where our target receiving stations are located.

Foxes hunt where the hens can be found

Choosing a band wisely improves the probability of successfully making contacts. If I have Internet access while operating portable, such as when activating a park for POTA, I check 2 things. First, which bands are indicated as having good propagation and, second, which bands have the most activators. If we call CQ on an empty band aren’t we boldy going where no ham has gone before?

Side by side

It can sometimes help if we park ourselves adjacent to another active frequency. I have used this technique myself hoping some of the big station’s hunters will hear my signal while tuning in to the other guy. For CW ops a 500Hz separation should be enough to avoid interfering with the other station; SSB ops will need to leave a bigger space.

It pays to advertise

It helps if people know we are going to be on-the-air. Perhaps we are planning to participate in a scheduled QRP event. During the event other QRP stations are actively seeking QRP stations to work. It is a good idea to post notice of our intention to participate ahead of time in online forums. When planning a QRP POTA activation, we can schedule the activation ahead of time on the POTA website (but don’t mention QRP!). Scheduling gives hunters advance notice of when to look out for us on-air. Some lucky QRP operators may even be on hunters’ Ham Alert lists.

The poodle and the bulldog

My current most used QRP radios include a QRP Labs low-band QMX – a cute little fella, but very fragile. Doesn’t like high SWR or any supply voltage over 12.00 volts. Also not very rugged, but it’s packed with features.

I bought this old steam-powered Yaesu FT-817 from a guy called Fred Flintstone in 2001. Back then Yaesu thought it was a good idea to make customers pay extra for luxuries like a memory keyer and a mechanical filter to narrow the receiver bandwidth. Being (like many hams, it seems) a miser I chose to build my own add-ons to make this great little multiband rig more usable. It has made a lot of QSOs for me. I have revived it after it spent a long time on the shelf. I like to think of this radio as a bulldog while the QMX is a clever little poodle.

The K4ICY 2/4-stage audio filter plugs into the radio’s headphone jack and provides a narrow audio passband. It is based on a single chip quad op-amp. I built it inside a Hammond aluminum box because when in a plastic enclosure it picks up near-field RF and amplifies that too. It is powered by an internal 9V battery.

My build of the K3NG Arduino-based CW memory keyer is equipped with just one control. Turning the rotary encoder adjusts CW keying speed on the fly (a useful feature during a POTA activation). Clicking the rotary encoder knob sends a pre-recorded CQ message. It is powered by a single 18650 LiIon cell with built-in buck boost to bring the voltage up from 3.7 to 5 volts.

Where, outside the box, do we venture next? Stay tuned, or subscribe. And, if you have any suggestions or questions, please leave a comment below.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#AmateurRadio #Antennas #CW #POTA #QMX

QRP? Are we out of our minds?

If we believe in QRP – I mean really, really believe – then we can make it work. Admittedly it’s like betting on a race between a tortoise and a hare; where would you put your money? If you read accounts written by diehard QRPers, do you ever see stories such as: “I went to the park with my latest QRP rig today and called CQ for five hours but only got 2 QSOs. On the way home I tossed that stupid rig in the river and bought a big-boy radio instead”? Of course not. Diehards enjoy the outing as much as the contacts. They get a thrill out of tickling the ionosphere even if the big bad D-layer swallows their RF and has a malignant chuckle to itself.

I am not a diehard, but I do like to operate QRP whenever it yields a good probability of actually getting contacts. On the other hand, when propagation conditions are unfavorable, or I cannot erect an efficient antenna, I am willing to switch to warp power to get the job done.

The FCC has given us guidance in the form of the Part 97 rules, and to paraphrase them:

“Use (only) as much power as in necessary to make the contact”

There are different ways to interpret that guidance. For many QRO operators it means “fire up the amp and let ‘er rip; life’s too short …”. The word “only” in the above may occasionally fall on deaf ears. QRPers, on the other hand, might see things differently and ask: “How can we make this work without increasing power?”.

There are days when 5 watts into a tiny coil-loaded whip is all you need; for other days there are tricks that can be employed to make a teeny-weeny smidgen of RF create the illusion of a really big-boy signal. The big secret is that it doesn’t matter how much signal the P.A. of our radios – big, small or tiny – presents at the antenna jack. What really counts is how much signal appears at the receiving end.

A military ELF (Extremely Low Frequency) radio station puts out a huge amount of power, but the amount reaching a submarine somewhere beneath the world’s oceans is only a few watts – effectively QRP. QRO operators can emulate that idea by using a dummy load with a random wire antenna attached. No tuner needed, any old antenna will work and the radio will always see a low SWR. It is said to work just fine but with the caveat that you will lose about 1 S-unit in signal strength due to loss in the dummy load. Would it be possible to invert that situation and transmit a very low power signal that a receiving station would perceive to be more powerful?

Don’t announce your handicap

If we call CQ and identify ourselves as QRP we are telling the world we are transmitting a teeny-weeny smidgen of a signal and that negatively influences the receiving station’s perception. In his book “Winning through intimidation” author Robert Ringer tells of clever benevolent techniques he employed in his sales career to dazzle potential clients into having a glowing perception of him. So let’s not mention our piddling power and allow the receiving station to assume we are just another regular ham station, or maybe even a superstation.

Use an efficient antenna

When conditions are right you can make contacts with a wet noodle. In most cases it makes sense to assume conditions are unfavorable and plan for the worst. That means putting up an efficient antenna – one that converts as much of our feeble signal as possible into radiated RF. If we can put up a gain antenna, even 3dB of gain, we will double our effective radiated power.

Don’t use a vertical antenna

Well, ok if we have to use a vertical antenna it should be raised off the ground. A ground mounted vertical antenna requires a lot of radials to be efficient. If it is raised as little as 1 meter above ground less radials will be required – maybe as few as 2.

A vertical antenna radiates equally in every direction so our feeble signal is spread around 360 degrees. If that signal can be focused to favor a specific direction, the receiving station will perceive it to be stronger. Greg KJ6ER’s POTA PERformer can effectively focus a signal even more than he intended by sloping the radiator away from the direction we wish our signal to go. Modeling with EZNEC shows a front/back ratio of over 8dB can be obtained by this method. That means more of our signal is being directed towards where our target receiving stations are located.

Foxes hunt where the hens can be found

Choosing a band wisely improves the probability of successfully making contacts. If I have Internet access while operating portable, such as when activating a park for POTA, I check 2 things. First, which bands are indicated as having good propagation and, second, which bands have the most activators. If we call CQ on an empty band aren’t we boldy going where no ham has gone before?

Side by side

It can sometimes help if we park ourselves adjacent to another active frequency. I have used this technique myself hoping some of the big station’s hunters will hear my signal while tuning in to the other guy. For CW ops a 500Hz separation should be enough to avoid interfering with the other station; SSB ops will need to leave a bigger space.

It pays to advertise

It helps if people know we are going to be on-the-air. Perhaps we are planning to participate in a scheduled QRP event. During the event other QRP stations are actively seeking QRP stations to work. It is a good idea to post notice of our intention to participate ahead of time in online forums. When planning a QRP POTA activation, we can schedule the activation ahead of time on the POTA website (but don’t mention QRP!). Scheduling gives hunters advance notice of when to look out for us on-air. Some lucky QRP operators may even be on hunters’ Ham Alert lists.

The poodle and the bulldog

My current most used QRP radios include a QRP Labs low-band QMX – a cute little fella, but very fragile. Doesn’t like high SWR or any supply voltage over 12.00 volts. Also not very rugged, but it’s packed with features.

I bought this old steam-powered Yaesu FT-817 from a guy called Fred Flintstone in 2001. Back then Yaesu thought it was a good idea to make customers pay extra for luxuries like a memory keyer and a mechanical filter to narrow the receiver bandwidth. Being (like many hams, it seems) a miser I chose to build my own add-ons to make this great little multiband rig more usable. It has made a lot of QSOs for me. I have revived it after it spent a long time on the shelf. I like to think of this radio as a bulldog while the QMX is a clever little poodle.

The K4ICY 2/4-stage audio filter plugs into the radio’s headphone jack and provides a narrow audio passband. It is based on a single chip quad op-amp. I built it inside a Hammond aluminum box because when in a plastic enclosure it picks up near-field RF and amplifies that too. It is powered by an internal 9V battery.

My build of the K3NG Arduino-based CW memory keyer is equipped with just one control. Turning the rotary encoder adjusts CW keying speed on the fly (a useful feature during a POTA activation). Clicking the rotary encoder knob sends a pre-recorded CQ message. It is powered by a single 18650 LiIon cell with built-in buck boost to bring the voltage up from 3.7 to 5 volts.

Where, outside the box, do we venture next? Stay tuned, or subscribe. And, if you have any suggestions or questions, please leave a comment below.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#AmateurRadio #Antennas #CW #POTA #QMX

A simple outside the box fix for a broken telescopic whip

“If it ain’t broke, don’t fix it”

Or conversely, if it is “broke” you have two choices. Order a replacement from the other side of the planet, and wait for the slow boat from China to navigate thousand of nautical miles across the stormy waters of international seas. Or, alternatively, and my preferred solution, is to see if it can be fixed. So when I managed to break the 18.5ft telescopic whip I had ordered from China a year or so ago, I was faced with that choice.

Hair of the dog

There is an old supposed remedy for the after effects of over indulgence in adult beverages. It is called the “hair of the dog that bit you”, often simplified to “hair of the dog”. The idea is that, in the morning, if you drink some more of the beverage that caused the problem you will recover. I rate that high on the skepticism index.

The dog that bit my antenna was another product from the same oriental source as the whip. It was a “top hat” designed for the PAC-12 antenna. This set of electric antlers proved too heavy for the whip that was never designed to carry them. The tip of the whip swayed rather wildly in the wind, before collapsing on the ground and decapitating itself in the process. The top hat survived but the top two sections of the whip parted company from the rest, never to be reconnected again.

What remained was 15 feet and 9 inches of whip that sat in a dark corner of the shack until, one day, a random firing of neurons in my brain came up with an idea. I call the idea “hair of the dog”; i.e. I wondered if I re-attached the top hat, the same one that caused the problem in the first place, to the shortened whip would it at least get me back on 20-meters?

The shortened wounded whip was a little too short to be resonant on the 20m band. Could the addition of a top (capacitance) hat lower the resonant frequency sufficiently to fix the problem? I embarked on an impromptu mission to find out.

Top loading a vertical whip is a very efficient way of convincing an electrically short antenna to resonate on a lower frequency. In effect, it increases the electrical length of the antenna. I have been chided by sagacious readers for using the term “electrical length”. The term may be technically incorrect but it makes it easier to understand what happens when an antenna is loaded. Is my top-loaded shortened whip as efficient as a full-length unloaded whip? I’ll leave that for the experts to comment upon.

There are advantages to a top-loaded vertical whip for field portable operators like myself. For a start, a shorter whip is less conspicuous. While activating a park back in the spring of this year, a uniformed Ontario Parks warden pulled up in her official pickup truck to see what I was up to. Ontario Parks wardens have the same authority as police officers when it comes to park rules and regulations. They can impose on-the-spot fines for infractions of a sometimes vague set of rules like “disturbing trees”. She told me that my long whip antenna had caught her eye. When I told her I was using Morse Code to contact other amateur radio operators and read out the list of all the states I had contacted, she was genuinely interested. We struck up a good rapport, especially when discussing which trail the resident park bear preferred. Although that encounter with officialdom went well I prefer to operate under the radar – nothing to see hear, move right along please.

As I write this we are well into fall. The winter months still lie ahead of us – 7 months of dreary, snowy, icy weather. So I took advantage of cool temperatures and still unfrozen ground to test my top-loaded shortened whip. I mounted the whip on my recently constructed support that uses PVC plumbing bits and part of a fiberglass driveway marker driven into the ground. For lucky readers in the southern states and other milder climates, a driveway marker is a thin pole used to identify the edges of a driveway when the snow comes. I use 5ft markers, and during last winter’s unusually heavy snowfall, they disappeared deep beneath the snow banks left by the snow plows on their daily runs. I gotta move to sunny Florida, snakes and gators be damned!

It might be considered folly to adopt a hair of the dog approach to fixing the whip but, of course, the lower sections of a telescopic whip are thicker than those at the top. Thicker sections are less likely to experience the wild, wind-induced, oscillatory motion that caused the initial problem. In fact, I had to shorten the whip by another two sections to bring resonance within the 20-meter band, thereby enhancing the physical rigidity even further.

For this initial backyard test I used a set of four 13ft radials that lie mostly on the ground. I know this isn’t the most efficient way of providing the “other half” of an antenna. I have now improved on that by extending the support pole to 43 inches (109cm) and replaced the ground radials with two sloping, above ground radials with links for 15m, 17m and 20m.

Very soon our ground will be frozen hard – like concrete – and then other support options will be required. However, this top-loaded short whip is going to be traveling with me on my winter POTA activations. It works fine business on 20m but, even with the whip extended to its full 15 feet 9 inches, the top hat can’t get it to work on 30-meters. Shortening the whip further (and collapsing the top hat’s “antlers”) allows the higher bands to be used, which is useful while band conditions create openings there.

When I broke the whip I started to look into finding a replacement. The Chameleon 25ft whip sounded interesting but then I watched a video in which one of these whips waved at the heavens during windy conditions. I could foresee another catastrophic collapse in my future if I went that route. I wondered whether a park warden might consider a very tall waving whip a hazard to other park users and wave an infraction notice at me in response. No, there had to be a safer solution and I think this top-loaded formerly broken whip fits the bill quite nicely.

Meanwhile, back in the shack …

Work continues on renovating my rigs to return to QRP operations when band conditions permit. I have been using my Yaesu FT-891 throughout the summer. I like to think of the FT-891 as a QRP rig with optional QRO capability. The trouble is, it is too easy to tweak the power just a little to give my signal a little more muscle. My QRP Labs QMX is a great little radio but it isn’t built for hostile environments – like Ontario winters. Unfortunately I chose the low band QMX when ordering so I am limited to 80m, 60m, 40m, 30m and 20m – no access to the higher bands which have been quite active lately. I do have another option – a rugged, pugnacious but rather old little rig that covers all bands. It was built back in the era when there were fewer options for QRPers and lacks some of the features we now take for granted. There is a way to add on the missing features; I’ll publish the details in an upcoming post.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#Antennas #CW #MorseCode #OutdoorOps #Portable #POTA #QMX

A simple outside the box fix for a broken telescopic whip

“If it ain’t broke, don’t fix it”

Or conversely, if it is “broke” you have two choices. Order a replacement from the other side of the planet, and wait for the slow boat from China to navigate thousand of nautical miles across the stormy waters of international seas. Or, alternatively, and my preferred solution, is to see if it can be fixed. So when I managed to break the 18.5ft telescopic whip I had ordered from China a year or so ago, I was faced with that choice.

Hair of the dog

There is an old supposed remedy for the after effects of over indulgence in adult beverages. It is called the “hair of the dog that bit you”, often simplified to “hair of the dog”. The idea is that, in the morning, if you drink some more of the beverage that caused the problem you will recover. I rate that high on the skepticism index.

The dog that bit my antenna was another product from the same oriental source as the whip. It was a “top hat” designed for the PAC-12 antenna. This set of electric antlers proved too heavy for the whip that was never designed to carry them. The tip of the whip swayed rather wildly in the wind, before collapsing on the ground and decapitating itself in the process. The top hat survived but the top two sections of the whip parted company from the rest, never to be reconnected again.

What remained was 15 feet and 9 inches of whip that sat in a dark corner of the shack until, one day, a random firing of neurons in my brain came up with an idea. I call the idea “hair of the dog”; i.e. I wondered if I re-attached the top hat, the same one that caused the problem in the first place, to the shortened whip would it at least get me back on 20-meters?

The shortened wounded whip was a little too short to be resonant on the 20m band. Could the addition of a top (capacitance) hat lower the resonant frequency sufficiently to fix the problem? I embarked on an impromptu mission to find out.

Top loading a vertical whip is a very efficient way of convincing an electrically short antenna to resonate on a lower frequency. In effect, it increases the electrical length of the antenna. I have been chided by sagacious readers for using the term “electrical length”. The term may be technically incorrect but it makes it easier to understand what happens when an antenna is loaded. Is my top-loaded shortened whip as efficient as a full-length unloaded whip? I’ll leave that for the experts to comment upon.

There are advantages to a top-loaded vertical whip for field portable operators like myself. For a start, a shorter whip is less conspicuous. While activating a park back in the spring of this year, a uniformed Ontario Parks warden pulled up in her official pickup truck to see what I was up to. Ontario Parks wardens have the same authority as police officers when it comes to park rules and regulations. They can impose on-the-spot fines for infractions of a sometimes vague set of rules like “disturbing trees”. She told me that my long whip antenna had caught her eye. When I told her I was using Morse Code to contact other amateur radio operators and read out the list of all the states I had contacted, she was genuinely interested. We struck up a good rapport, especially when discussing which trail the resident park bear preferred. Although that encounter with officialdom went well I prefer to operate under the radar – nothing to see hear, move right along please.

As I write this we are well into fall. The winter months still lie ahead of us – 7 months of dreary, snowy, icy weather. So I took advantage of cool temperatures and still unfrozen ground to test my top-loaded shortened whip. I mounted the whip on my recently constructed support that uses PVC plumbing bits and part of a fiberglass driveway marker driven into the ground. For lucky readers in the southern states and other milder climates, a driveway marker is a thin pole used to identify the edges of a driveway when the snow comes. I use 5ft markers, and during last winter’s unusually heavy snowfall, they disappeared deep beneath the snow banks left by the snow plows on their daily runs. I gotta move to sunny Florida, snakes and gators be damned!

It might be considered folly to adopt a hair of the dog approach to fixing the whip but, of course, the lower sections of a telescopic whip are thicker than those at the top. Thicker sections are less likely to experience the wild, wind-induced, oscillatory motion that caused the initial problem. In fact, I had to shorten the whip by another two sections to bring resonance within the 20-meter band, thereby enhancing the physical rigidity even further.

For this initial backyard test I used a set of four 13ft radials that lie mostly on the ground. I know this isn’t the most efficient way of providing the “other half” of an antenna. I have now improved on that by extending the support pole to 43 inches (109cm) and replaced the ground radials with two sloping, above ground radials with links for 15m, 17m and 20m.

Very soon our ground will be frozen hard – like concrete – and then other support options will be required. However, this top-loaded short whip is going to be traveling with me on my winter POTA activations. It works fine business on 20m but, even with the whip extended to its full 15 feet 9 inches, the top hat can’t get it to work on 30-meters. Shortening the whip further (and collapsing the top hat’s “antlers”) allows the higher bands to be used, which is useful while band conditions create openings there.

When I broke the whip I started to look into finding a replacement. The Chameleon 25ft whip sounded interesting but then I watched a video in which one of these whips waved at the heavens during windy conditions. I could foresee another catastrophic collapse in my future if I went that route. I wondered whether a park warden might consider a very tall waving whip a hazard to other park users and wave an infraction notice at me in response. No, there had to be a safer solution and I think this top-loaded formerly broken whip fits the bill quite nicely.

Meanwhile, back in the shack …

Work continues on renovating my rigs to return to QRP operations when band conditions permit. I have been using my Yaesu FT-891 throughout the summer. I like to think of the FT-891 as a QRP rig with optional QRO capability. The trouble is, it is too easy to tweak the power just a little to give my signal a little more muscle. My QRP Labs QMX is a great little radio but it isn’t built for hostile environments – like Ontario winters. Unfortunately I chose the low band QMX when ordering so I am limited to 80m, 60m, 40m, 30m and 20m – no access to the higher bands which have been quite active lately. I do have another option – a rugged, pugnacious but rather old little rig that covers all bands. It was built back in the era when there were fewer options for QRPers and lacks some of the features we now take for granted. There is a way to add on the missing features; I’ll publish the details in an upcoming post.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#Antennas #CW #MorseCode #OutdoorOps #Portable #POTA #QMX

😆 Oh, look! Another "enlightening" article for #hobbyists who apparently can't Google the basics of #radio. What a revelation: #antennas exist and radios don't just magically work! 📻✨
https://lcamtuf.substack.com/p/radios-how-do-they-work #technews #enlightenment #HackerNews #ngated

From Yashwant Gupta, "Phased Arrays":

"For identical elements, this phased array gives a sensitivity which is n times the sensitivity of a single element, for point source observations. The beam of such a phased array is much narrower than that of the individual elements, as it is the process of adding the voltage signals with different phases from the different elements that produces the narrow beam of the array pattern."

6/8

#radioastronomy #interferometry #phasedarray #antennas

From Yashwant Gupta, "Phased Arrays":

"For identical elements, this phased array gives a sensitivity which is n times the sensitivity of a single element, for point source observations. The beam of such a phased array is much narrower than that of the individual elements, as it is the process of adding the voltage signals with different phases from the different elements that produces the narrow beam of the array pattern."

6/8

#radioastronomy #interferometry #phasedarray #antennas

Monopod's max extension is 60 inches (153mm), Collapsed is 19 inches. 19 inches is almost exactly a quarter wave on 144Mhz (2m) ham radio. Fully extended goes to down to 39Mhz... so it could be a quarter wave antenna on 50Mhz (6 meters)... calculating in meters is easier, 153mm = 1.53m, 1.53mx4 = 6.12meter lowest wavelength. #hamradio #geeky #math #antennas

Randomly found a nice little site that's still using Tripod web hosting:
https://cheatthezone.tripod.com/wireless/colinear.html

It seems to be the canonical page that most other instructions / YouTube videos / etc. refer to when describing DIY co-linear antenna construction, too.

#antennas #HamRadio #AmateurRadio #radio #OldInternet

From ⁨⁨⁨⁨⁨#AnnafromUkraine⁩⁩⁩⁩⁩ @[email protected]
🧵 👇

DEEP STRIKE OVER 1000 KM: CHEBOKSARY ON FIRE Vlog 1096: War in #Ukraine

The Special Operations Forces struck the “#Borisoglebsk” #airfield, where Russian fighter jets are based. In #Cheboksary, #Chuvash Republic, #Russia, Ukrainian #kamikaze #drones have struck the "#VNIIR-Progress" plant, which manufactures "#Kometa"-type #antennas used to protect Russian military #drones and #missiles from Ukrainian electronic warfare systems.

1/2

From ⁨⁨⁨⁨⁨#AnnafromUkraine⁩⁩⁩⁩⁩ @[email protected]
🧵 👇

DEEP STRIKE OVER 1000 KM: CHEBOKSARY ON FIRE Vlog 1096: War in #Ukraine

The Special Operations Forces struck the “#Borisoglebsk” #airfield, where Russian fighter jets are based. In #Cheboksary, #Chuvash Republic, #Russia, Ukrainian #kamikaze #drones have struck the "#VNIIR-Progress" plant, which manufactures "#Kometa"-type #antennas used to protect Russian military #drones and #missiles from Ukrainian electronic warfare systems.

1/2

From ⁨⁨⁨⁨⁨#AnnafromUkraine⁩⁩⁩⁩⁩ @[email protected]
🧵 👇

DEEP STRIKE OVER 1000 KM: CHEBOKSARY ON FIRE Vlog 1096: War in #Ukraine

The Special Operations Forces struck the “#Borisoglebsk” #airfield, where Russian fighter jets are based. In #Cheboksary, #Chuvash Republic, #Russia, Ukrainian #kamikaze #drones have struck the "#VNIIR-Progress" plant, which manufactures "#Kometa"-type #antennas used to protect Russian military #drones and #missiles from Ukrainian electronic warfare systems.

1/2

From ⁨⁨⁨⁨⁨#AnnafromUkraine⁩⁩⁩⁩⁩ @[email protected]
🧵 👇

DEEP STRIKE OVER 1000 KM: CHEBOKSARY ON FIRE Vlog 1096: War in #Ukraine

The Special Operations Forces struck the “#Borisoglebsk” #airfield, where Russian fighter jets are based. In #Cheboksary, #Chuvash Republic, #Russia, Ukrainian #kamikaze #drones have struck the "#VNIIR-Progress" plant, which manufactures "#Kometa"-type #antennas used to protect Russian military #drones and #missiles from Ukrainian electronic warfare systems.

1/2

From ⁨⁨⁨⁨⁨#AnnafromUkraine⁩⁩⁩⁩⁩ @[email protected]
🧵 👇

DEEP STRIKE OVER 1000 KM: CHEBOKSARY ON FIRE Vlog 1096: War in #Ukraine

The Special Operations Forces struck the “#Borisoglebsk” #airfield, where Russian fighter jets are based. In #Cheboksary, #Chuvash Republic, #Russia, Ukrainian #kamikaze #drones have struck the "#VNIIR-Progress" plant, which manufactures "#Kometa"-type #antennas used to protect Russian military #drones and #missiles from Ukrainian electronic warfare systems.

1/2

Landsat At Work – Better Wireless Communication - National Land Cover Database (NLCD), Based On Landsat, Helps Plan Clear Signal
--
https://www.usgs.gov/centers/eros/news/landsat-work-a-path-better-wireless-communication <-- shared article
--
https://www.usgs.gov/landsat-missions <-- shared about Landsat
--
https://www.usgs.gov/centers/eros/science/annual-national-land-cover-database <-- shared about NLCD
--
#GIS #spatial #mapping #Landsat #remotesensing #satellite #earthobservation #fedscience #usecase #USGS #EROS #cellphone #mobilephone #telecommunications #communications #cost #benefit #wireless #towers #antennas #landcover #landuse #NLCD #radio #frequency #siting #lineofsight #clutter #economics #risk #hazard #signal #signalquality #USA #value #returnoninvestment
@USGS @USGS_EROS

25 Years a Ham and Still Learning

I actually got my “ticket” a little late in life. I spent many years as an SWL, then college, career and a family took priority. By the time my wife and I became empty-nesters I had combined my passion for radio and Space “the final frontier” by chasing satellites; military satellites mainly. I formed the HearSat group dedicated to monitoring Low Earth Orbiting satellites. My account of a unique method of decoding the signals from Russian navigation satellites was kindly published by Monitoring Times magazine. At the time I felt there were so many fascinating signals flying around that there was nothing of value I could contribute by adding my own. However that feeling didn’t last long and eventually I bought a study guide, passed the written test and became a ham.

Now, I am into my 25th year in this great hobby. Frankly I was never satisfied with using a radio just to rag chew; I felt an urge to experiment – to contribute something useful to the science of radio communications. I didn’t fully realize it at the time, but I was at the bottom of a steep hill that I am still climbing, learning with every step. As my personal lifelong learning journey progresses I am proud to share knowledge gained here at Ham Radio Outside the Box.

“In times of change, learners inherit the earth; while the learned find themselves beautifully equipped to deal with a world that no longer exists.” – Eric Hoffer

Several weeks ago Ham Radio Outside the Box introduced a rather unique antenna idea, called the Coil-Loaded End-Fed Half Wave (CLEFHW). It is a telescopic whip that is inductively base-loaded to become an electrical half-wave. What is the purpose? To create a backpackable antenna with a very small footprint achieved by eliminating the need for a long counterpoise or system of radials. It worked very well – for a while. Then I began tinkering with it; I call it “continuous improvement” and it stopped working properly.

“If it ain’t broke …”

The antenna started to experience unstable SWR. Then the great snowstorms of February 2025 arrived and I could no longer get outside to investigate. Undaunted, I set up a wire in my basement “lab” to simulate the whip and was able to adjust the antenna to get a good SWR again. All was good – until an unusual warm spell hit and I was able to get out to a local park to do a POTA activation. Suddenly, the good SWR was gone again. Abandon the activation? No, improvise and adapt! I pulled my ham-brew “Old Barebones” Z-match out of my pack and finished the activation.

Back at the shack I was determined to find out what had gone wrong. The park I had visited sits on shale stone rock just beneath the soil and is right alongside one of the Great Lakes. Previous activations at that park had given spectacularly good results.

It ain’t gonna work John, give up and go have a beer

The snow still lay deep and crisp and even on my backyard but I managed to shovel my raised wooden deck clear and continue the investigation. That was the start of a very frustrating series of antenna trials. It can be tempting at times to quit – “it ain’t gonna work John, give up and go have a beer”. But, I remembered my college physics training: experiment – document the results – change one thing at a time – document the new results – make further changes as required and repeat until success is achieved.

The most important part of that process is to document the results at each and every step. I keep a small spiral bound notebook and a pencil nearby while I tinker in my basement lab. That makes it easier to review what went wrong and when. Yes, it’s tedious to put down the soldering iron and pick up the pencil, but it does make a big difference in the end.

So what was learned? It seemed a fair assumption that an 18.5ft whip, replaced with an 18.5ft wire would perform pretty much the same. But oh, no John, no John, no! There was another parameter involved that hadn’t been considered. The lab experiment with the wire took place in the nice, warm environment of my basement replete with space heater and a constant supply of hot beverages. But the basement lies 6 feet below grade – could that be an issue?

The carefully adjusted antenna with the 1.2:1 SWR was then carried up, up and away to the deck, out into the cruel Big Blue Sky Shack where the temperature was hovering around freezing. The 18.5ft wire was replaced with the telescopic stainless steel whip which, with all 13 sections extended, was also 18.5ft long. I confidently powered up my rig and set the mighty micro QMX to monitor SWR. “Should be pretty close to the same SWR I got in the basement” methought. But then disappointment haunted all my dreams. The lilliputian radio gave me the bad news: SWR 2.6:1.

A bit of a stretch

Previous learning experiences had taught that any physically short antenna that is artificially extended to it’s electrical full length by means of a loading coil tends to exhibit a very high Q. The CLEFHW uses a base loading coil to extend its physical length of 18.5 feet to an electrical length of approximately 33 feet which is a half wavelength on 20m. If the inductance of the loading coil isn’t right in the bullseye of the required value, the electrical characteristics can be subject to unexpected change.

But perhaps the unexpectedly high SWR out on the deck was influenced by another factor. Yes, the basement lab is 6 feet down below ground while the deck is 2 feet above the ground. How to compensate for this? Is the CLEFHW going to need a custom coil for each and every deployment? Maybe it will, but there is a solution that we will get to in a moment.

“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
― Nikola Tesla

Back in the lab the loading coil was rewound with nearly enough inductance to earn a place in Nikola Tesla’s lab.

The idea was that turns could be removed until the SWR settled down to an acceptable level. The target was less than 1.5:1. It worked! The SWR out on the deck came down to 1.10:1.

Just a cotton pickin’ minute Einstein…

The victory dance had to be put on hold as another doubt surfaced. The SWR measured out on the shale stone ground in the park was different to the SWR measured on the hardwood over concrete floor of the basement lab. The SWR out on the deck had been different again. A pause and a little stroking of the chin while the old gray matter overheated with intense thought. This deck, said the voices inside my head, is 2 feet above the ground. Do we have another variable to throw into the equation here?

The base of the antenna is at the top of the backpack frame and when the pack sits on the ground, as intended during outdoor operating sessions, it is only about a foot and half above the ground. The antenna is an almost vertical shortened End-Fed Half-Wave (it is sloped to give it some directionality). So is proximity to ground another factor to consider?

The whole backpack rig, antenna and all, was beamed over to an area of grass just beyond the deck. Here we go again, with everything exactly as it was up on the deck, the SWR grew legs and climbed up over 2:1 again.

The Ultimate Lossless Tuner?

The simple solution would have been to pull out “Old Barebones” (Z-match) again and bring those pesky standing waves under control. But I had another cunning plan. By leaving some extra turns on the coil I could increase the inductance beyond what is required to load the whip and use the whip itself to adjust the SWR.

Brilliant! It worked. The final iteration of the coil (nothing is ever really final) involves three taps near the top of the coil to leave some inductive flexibility to accommodate persnickety ground conditions. An SWR of 1.09:1 was obtained with the pack out on the grass. But, it was necessary to collapse two sections of the whip to get there. Interestingly, adjusting the whip length retunes the antenna without introducing any further loss; it simply restores the electrical length of the loaded whip to a half-wave.

So now, once again, the Ham Radio Outside the Box Coil-Loaded End-Fed Half-Wave antenna is ready for action. Lessons learned. Oh, and – Note to Self – move onto another project John – don’t tinker with things that work already!

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#Antennas #CLEFHW #Ground #OldBarebonesZMatch #POTA #QMX

Finalizing the "Wall of SDR" ...

P25 in to Trunk Recorder

Multiple SDR into Kismet Wireless for 315/433/915/1090 and also a BT TIC for BTLE monitoring

Multiple SDR into SDR++ Server for local Amateur Radio Repeaters monitoring

Dedicated line to another machine for just specific testing.

And then finally documented.

#SDR #SoftwareDefinedRadio #AmateurRadio #HAMRadio #RTLSDR #BladeRF #KismetWireless #Kismet #WiFi #BTLE #Diagram #Documentation #WiresWiresWires #Antennas #ADSB #1090

A File Worth Having: Bob’s guide to building an Electrically Small Resonant Loop Antenna for Mediumwave Reception

https://swling.com/blog/2024/12/a-file-worth-having-bobs-guide-to-building-an-electrically-small-resonant-loop-antenna-for-mediumwave-reception/

#Antennas #BobColegrove #HomebrewMagLoopAntenna #LoopAntennas

Sci-Fi Inspired Antenna Adjusts to Signal Needs
https://spectrum.ieee.org/smart-materials-morphing-antenna
#ycombinator #antennas #shapeshifting #additive_manufacturing #signal_processing #4d_printing

"Revolutionizing radio tech: 3D printing is set to transform the industry! From antennas to RF components, the ability to print complex shapes and materials opens up new possibilities for customization, cost-effectiveness, and innovation. With faster prototyping and on-demand production, the future of radio is 3D printed!" #3Dprinting #RadioTech #Innovation #Customization #CostEffective #RFComponents #Antennas #google ##huggingface #perchance #chatgpt #aiart #artbasel2034 #michaelpaulino

"Revolutionizing radio tech: 3D printing is set to transform the industry! From antennas to RF components, the ability to print complex shapes and materials opens up new possibilities for customization, cost-effectiveness, and innovation. With faster prototyping and on-demand production, the future of radio is 3D printed!" #3Dprinting #RadioTech #Innovation #Customization #CostEffective #RFComponents #Antennas #google ##huggingface #perchance #chatgpt #aiart #artbasel2034 #michaelpaulino

"Revolutionizing radio tech: 3D printing is set to transform the industry! From antennas to RF components, the ability to print complex shapes and materials opens up new possibilities for customization, cost-effectiveness, and innovation. With faster prototyping and on-demand production, the future of radio is 3D printed!" #3Dprinting #RadioTech #Innovation #Customization #CostEffective #RFComponents #Antennas #google ##huggingface #perchance #chatgpt #aiart #artbasel2034 #michaelpaulino

It took all day (because I wanted everything to be neat and orderly) but I got my new loaded fan dipole up and on the air.

From HyPower Antennas, this is a clever design. The 80m loading coils are positioned where the ends would be for 20 meters, so you end up with that leg covering 80 and 20. I added a 30m leg, which also works on 10m. So all told this antenna is resonant on 80, 40, 30, 20, and 10m. My configuration requires just a little nudge by the antenna tuner, as expected.

The other antennas are for OTA television (and they feed into triple band-pass filters to try very hard to keep the ham bands out of the preamp, though I suspect 10m's first harmonic might end up interfering with low VHF. OTOH, Elecraft's TX filters are excellent, so it may not be an issue).

10m was wide open, and I quickly made a contact with mainland China on 28.074 with about 30 watts.

All told a lot of work, but fun, and doing a science is always rewarding.

#HamRadio #AmateurRadio #antenna #antennas #antennae

Communications 📶 with #Odysseus remain limited and will end when sunlight ☀️ is no longer shining on the #SolarPanels. Its #antennas 📡 are not pointed back at #Earth, greatly slowing the rate that data can be sent back https://www.nytimes.com/2024/02/26/science/odysseus-moon-lander-photos.html

#IM1 #IntuitiveMachines #MoonLander

@f1sls 23 and 33+
23 for sealing wire and connector.
33+ to protect the 23 tape.

When you have air inside box you can have moisture inside.
I put plastic dip to protect.
You can try a electrical Magic gel inside the box (I never using this with radio équipements)

#antennas #connectors #DXEngineering

@f1sls 23 and 33+
23 for sealing wire and connector.
33+ to protect the 23 tape.

When you have air inside box you can have moisture inside.
I put plastic dip to protect.
You can try a electrical Magic gel inside the box (I never using this with radio équipements)

#antennas #connectors #DXEngineering