#antennas — Public Fediverse posts

This Tiny Gadget Lets Sports Fans Watch Free OTA Games on Their Phones Without Paying for Streaming

https://fed.brid.gy/r/https://cordcuttersnews.com/this-tiny-gadget-lets-sports-fans-watch-free-ota-games-on-their-phones-without-paying-for-streaming/

This Tiny Gadget Lets Sports Fans Watch Free OTA Games on Their Phones Without Paying for Streaming

https://fed.brid.gy/r/https://cordcuttersnews.com/this-tiny-gadget-lets-sports-fans-watch-free-ota-games-on-their-phones-without-paying-for-streaming/

TechTip #3 Radials and counterpoises

TechTips on Ham Radio Outside Outside the Box are occasional short posts on specific technical topics. But beware, along with regular posts here on this blog, the content is not a definitive technical treatise and should not be read as such. I write about my own opinions and experiences; your opinions and experiences may be quite different. I welcome constructive feedback either in the comments or, if you prefer, by direct email.

“All lies and jest …

Still a man hears what he wants to hear and disregards the rest”. Paul Simon and Art Garfunkel sang those words in their song “The Boxer”. The words reflect how hams often react when our long-held, cherished beliefs are challenged. “My antenna just works, I don’t care about all that technical stuff” is a view I have heard – especially when the antenna cost hundreds of dollars. And nothing creates more exothermic debate than the subject of radials. Or is that counterpoises?

Definitive definitions

On Ham Radio Outside the Box, when the word “counterpoise” is used, it refers to the “other half of an antenna”. The “other half” could be 120 buried radials, or it could be a “magic carpet” (Faraday cloth). It could be a ground rod driven vertically into the ground. It could even be the ubiquitous (and apparently blessed by angels) 17 feet of wire laid on the ground. That magic length of 17 feet has been proved by thousands of QSOs so why care about all that technical stuff? Eh?

When you read the word “radial” here on Ham Radio Outside the Box it refers to a length of wire. A counterpoise may comprise one or one hundred and twenty radials. Radials could be buried in a shallow grave inches below the surface or they might be raised above ground. Buried radials – or even radial wires laid on the ground – are detuned by the ground and can be any length. Longer radials work better on the lower bands.

“Crickets are singin’ and lightning bugs are floatin on the breeze”

It’s been a while since I went “Fishing in the Dark” (for contacts on the radio) but I do spend a lot more of my on-air time out in the Big Blue Sky Shack, usually on a sunny afternoon – even if it’s only out in the backyard. If we venture out to a park to spend a couple of hours playing radio, we really aren’t going to waste that time laying out 120 radials. If an antenna needs ground radials I lay out between 4 and 8 of them. I know my antenna’s efficiency will be compromised, and I acknowledge the physics, but field expediency is the prime directive. Heck, I usually operate QRP in the field too; maybe I should try “QLF” (sending CW with my left foot) too. Some of my code buddies claim I’ve already mastered QLF!

Floatin’ on the breeze

Compromising efficiency is not mandatory. If we raise the antenna (a vertical whip) above ground. Now just a couple of tuned radials is as efficient as a rat’s nest of wires on the ground. A couple of radials? Why not just one radial? I was asked that question recently by a Ham Radio Outside the Box reader. I had to put on my physics graduate gown and mortarboard while I thought about that.

I started with the idea of a vertical dipole – that’s a quarter wave of wire on top of another quarter wave of wire with the feedpoint in the middle. Now let’s bend that dipole a little. Now it looks like a vertical radiator with a quarter wave high flying counterpoise. If we keep that configuration well above ground it should still be as efficient as a dipole.

I got wires in low places

How low can we go? My theory (which is open to debate) is based on interaction between that raised radial and the ground. The current in the radial wire induces an out of phase image in the ground. In the near field the image wave and the wave in the radial wire tend to partially or fully cancel each other.

The amplitude of the image wave in the ground varies based on two things. (1) the amplitude of the current in the radial, and (2) how close the radial is positioned with respect to ground. A high radial has almost no interaction with the ground, whereas a low radial will have a much greater interaction.

Now, let’s consider this: we can reduce the amplitude of the current wave in the counterpoise if the current is shared between more than one radial. Two radials each carry half the current; four radials each carry a quarter of the current. The lower the current, the lower the canceling effect of the image in the ground.

So we can conclude that it is fine and dandy to use low radials if there are a lot of them. On the other hand, a single radial should be kept well clear of the ground. Does that make sense, or didn’t I wake enough brain cells with my morning espresso today?

But wait, there’s more …

If the objective is to reduce the interaction with the ground, and the amplitude of the current wave in the radial wire(s) is a factor, there is another way – reduce transmitter power. See, QRP ain’t so bad after all!

Incidentally, the image wave in the ground travels more slowly than the current wave in the radial. If the length of the radial wire is one full wavelength, or more, the two waves eventually are in phase and the current is reinforced instead of being canceled. That is how Grasswire antennas work.

Murphy’s opinion

Electrically, a single raised radial will be efficient, subject to the conditions discussed. According to Murphy’s Law, if you use a single raised radial, you better anchor that antenna down good or the tension in that radial wire is gonna pull your antenna over. Murphy says two radials, 180 degrees apart, will keep it up.

A 5-Band, Lazy-L, Linear-Loaded, Ladder Line Antenna (aka the “5B6L”)

About a year ago I mentioned an antenna devised by Peter Waters G3OJV that used a 13 feet (4 m) vertical wire to create a multiband antenna. I used Peter’s idea to create “A Simple, Low Profile, Multiband Antenna for POTA“. The antenna was designed to work on 20m, 17m, 15m, 12m and 10m with the aid of a tuner. But, I discovered a small problem on the 17m band. If we do the elementary calculation for the length of a quarter-wave radiator at the bottom end of the band (18.068 MHz) we find that it works out to be 12.95 ft – just a whisker short of the 13 ft recommended by G3OJV. So why is that a problem?

The problem arises because the antenna uses a 4:1 unun at the feedpoint. Since the 13 ft length is already almost resonant on 17 meters, the 4:1 unun makes the job of the tuner much harder. That did indeed prove to be the case when I tested my derivative in the field. So, I made a small change when designing the new 5B6L antenna – I increased the length to 14 feet (4.2672 meters) – well … not quite true, but that is the underlying principal behind the linear-loaded equivalent.

Here are the calculated lengths of a quarter-wave radiator at the mid-point of each of the five bands of interest:

A 14ft radiator slips nicely in between the 20m and 17m quarter wavelengths and becomes a “random length” on all 5 bands. Nice. But this is a linear-loaded antenna made from ladder line. Linear-loading shortens the required length by around 30%. Fourteen feet, shortened by 30% works out to 9.8 feet (~3 meters). After field adjustments I settled on a length of 9.75 ft (a little less than 3 meters).

Lose the radials!

I wanted this antenna to be what could be loosely described as a random length dipole – two equal lengths of ladder line (each shorted at one end) so that was how it was constructed. Now we have the benefit of versatility. It could be erected as a traditional dipole although with two very short arms it would be tricky to get it up in the air. It could also be erected as a vertical dipole on a support pole about 7 meters (23 feet) tall like my Spiderbeam. But that would make it difficult to orient the coax feedline so that it comes away from the antenna at 90 degrees, as is required to prevent the feedline picking up some of the radiated signal. Perhaps a sloper would work; now that is a very viable solution.

How ‘Bout a Lazy-L?

One of the YouTube channels I follow is “Jim’s Cool Stuff“. In one of his videos Jim suggested using a “Lazy-L” orientation of a vertical simple wire radiator and single raised radial wire. Why? The purpose is to increase the take-off angle. A vertical antenna usually has a very low take-off angle which is great for chasing DX, but what about shorter-range contacts? From my location in Southern Ontario, Canada it is only a short hop down to the north-eastern states in the USA. The US northeast has a very large concentration of amateur radio operators many of which participate in popular activities like POTA. A vertical antenna is likely to send my signal whistling over their heads, or at the very least, be received at a reduced level.

A Lazy-L configuration optimizes radiation to favor short to mid-range contacts by raising the take-off angle to achieve much shorter hops. Does it work? Yes indeed, during test operations I have been able to make contacts, just over the shallow puddle they call Lake Erie, into Pennsylvania, and across Lake Ontario into the state of New York, with quite respectable signal reports for my QRP CW signal.

But what about DX?

Stations on the west coast of the US or western Canada could be considered almost DX – each is thousands of kilometers away. No problem! I said this antenna has versatility. The Lazy-L configuration can be re-oriented to a straightforward regular vertical with a raised counterpoise very easily. In fact the angle at which the radiating element leans can be adjusted to find an optimum at which near-DX and short hop stations all fall within its radiation pattern.

How to Build a 5B6L

The following describes construction of a 5-Band, Linear-Loaded, Ladder Line antenna that can be operated on 20m, 17m, 15m, 12m and 10m with the use of a tuner. Materials needed are:

• Ladder Line. I recommend stranded conductors because this makes the ladder line more flexible than solid copper conductors. Use of the 5B6L as a field portable antenna may stress solid conductors and lead to failures.
• a 4:1 unun. This item can be purchased or you can build your own using twin lead speaker wire (or similar) wound around a type-43 ferrite toroid

Instructions

• Cut two lengths of ladder line each 10 feet (3 meters) long. These may need to be trimmed during testing.
• Connect the two conductors of each piece of ladder line together at one end only.
• At the other end of each piece of ladder line, cut off the end of one of the conductors.
• Strip the insulation from the other conductor – this will be connected to the 4:1 unun.
• Connect each piece of ladder line to the unun.

Erection of the antenna

Attach a coax feedline to the 4:1 unun. A tuner may be inserted at this end if desired. For practical purposes, unless a very long coax is used, the SWR losses in the coax will not be significant so a tuner at the radio end can be used.

Set up your choice of pole, or other support, attach one end of the antenna to the top of the pole. The other end of the sloping radiating element (the feedpoint) should be supported on a short stick.

The other half of the antenna serves as a raised counterpoise and its far end can be supported by, for example, a trekking pole.

The slope angle can be adjusted by simply moving the counterpoise support sticks. See what works best for you. The whole antenna can be quite stealthy. I erected mine on only a 10 feet high pole. Efficiency may be improved by using a taller support but I prefer stealth when operating in public spaces. Tall antennas arouse suspicion!

The end is nigh!

A generous friend donated a lot of ladder line some time ago and I have used all but a few feet of it. Maybe it’s time to experiment with something different. So my next project – take a deep breath – is something I have been writing about in unflattering terms recently – a short, base loaded whip! What? Have I been enjoying too much Scottish champagne? Well, I thought it would be an interesting challenge to see how efficient I could make a short-ish whip antenna with a base-loading coil. A prototype has been constructed and has made contacts in backyard tests (with my helping fingers tapping on the key ). When the design has been completed you will be able to read about here on Ham Radio Outside the Box. 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.

An alternative mini-GTU design by Tim KQ4TQ

As I mentioned in the last post on Ham Radio Outside the Box, I received a surprise package in the mail from Tim KQ4TQ in Georgia. Tim sent me his build of a mini Ground Tuning Unit (GTU) that is simpler in design than the one I built. Tim’s design is a single inductor of 3 microhenries wound on a T82-6 toroid, in series with a 10-355pF polyvaricon. The polyvaricon used in my original Mini-GTU had a maximum capacitance of only 160pF (I extracted it from a charity store AM/FM radio).

Tim’s GTU was quickly deployed out in the Ham Radio Outside the Box antenna test range (my backyard in Owen Sound, Ontario) for a full evaluation. Tim warned that tuning is very sharp and a steady hand is needed to get the best setting. My aging hands are definitely not as steady as they used to be but I found it was actually quite easy to tune.

The original Mini GTU versus the KQ4TQ GTU

The original Mini GTU recently described here on Ham Radio Outside the Box has 4 inductors, each with a shorting switch, in series with a polyvaricon. The purpose of the switches is to enable binary selection of inductance between 0.5 and 15.5 microhenries. By experiment I had discovered that easiest tuning is obtained when the inductance is low (and, of course, higher inductance introduces ohmic loss). So the objective was to binary select an inductance, starting at the lowest value (0.5uH), adjust the capacitance by rotating the polyvaricon knob and measuring the effect on the antenna’s SWR. Then, if an acceptable SWR is not obtained, add more inductance and measure again. In practise it was discovered that a value of 2 or 3 microhenries works for most of the bands tried. By contrast Tim’s GTU, with its single inductance of 3uH simplifies the tuning procedure. Actually, either design works equally well although the original Mini GTU with 4 inductors can also be deployed as an L-match with precision inductance selection.

I reluctantly felt the need to repackage Tim’s GTU in order to implement a couple of design enhancements. When I nervously advised Tim of what I had done he graciously accepted the ideas. Here are the changes:

The original enclosure (see picture earlier in this post) required an external BNC to binding post adapter which looked clumsy. My first mod was to build Tim’s GTU into a small plastic box from the “River in Brazil” company. An LED and sensor circuit was included to give a visual indication of the best setting of the GTU.

I chose a high brightness LED since the device will often be used in bright sunshine. We do actually get bright sunshine during the brief interval between snow storms that we call “summer” here in Ontario. As I write this my home air-conditioning is actually running for the first time – but we will back to heating again in a couple of days.

A quick reminder about the function of a GTU. A GTU is a ground tuner, it’s purpose is to tune a compromise counterpoise to increase its current flow. Increasing the current flow in the counterpoise allows increased current to flow in the radiator portion of the antenna.

Why use a compromise counterpoise? It is sometimes necessary when setting up in a very restricted space location.

Here is where I went “outside the box” in my thinking. It might have been logical to place the current sensor in the ground circuit. But the end objective is to improve current flow in the radiator, so why not just place the current sensor in the radiating element path? In fact, that is what I did. If you look at the internal picture of the repackaged GTU you will see a wire passing through the inductor (red winding), connecting the binding post at the left end (where the radiator wire connects) to the BNC at the right hand end.

Two small circuit boards are visible. The one on the left contains the high brightness LED, recycled from an old defunct SLA battery box. The other small board contains a Germanium diode, RF bypass capacitor and current limit resistor for the LED. The toroid with the red coil turns is an FT82-43; it forms a 10:1 transformer used to sense the level of current flowing in the radiator path which is then displayed by the LED.

So does it work?

This is that rubber hits the road moment. Appropriate since I just had the winter tires taken off my truck. Those tires, dual-range 4-wheel drive and an economical yet powerful V8 engine got me out of more than one deep snow drift last winter. But, anyway, back to the topic in hand, does it work?

Mike W4AEE recently commented: “why are you using a capacitive coupling plate on top of lossy soil? I don’t understand why you would want to put this huge amount of loss in the antenna system. You’re forcing exchange currents between the vertical element ground system to try to flow through a high resistance that’s in series with the circuit. A single counterpoise wire thrown out on the ground would be better than that.”

Mike has a valid point. But, of course, the objective was not to engineer a perfect antenna the Physics Department would endorse. The original design called for a hiking antenna that can be rapidly deployed in a small clearing in the woods. There are many locations I venture into where it simply isn’t possible to lay out an efficient set of radials. A capacitance plate on the ground is indeed a compromise – as was revealed in a recent post here when I rejected the magic carpet ground plane idea as being inefficient. I tried alternative grounds. Here are a couple of them:

First up was a small hand cart I built specifically for ham use. There is a DC path all the way through the aluminum tubing to the steel mesh platform at the bottom. The mesh platform is a capacitive plate for use with a GTU.

At the top you can see the linear-loaded 20m band radiating element made from commercial 450 ohm window line. Did the LED glow when RF was applied? Yes sir and the measured SWR was 1.3:1. That’s good isn’t it? No, I’ll explain in a minute.

Next up was a 22ft long steel wire marker fence along the side of my driveway. The 3ft high fence was built as a guide when snow piles up in the winter. It didn’t work too well the last couple of winters when it disappeared beneath the snow! Just about the same RF result was obtained as with the hand cart.

Heck, I made plenty QRP CW contacts so why wasn’t I happy with the magic carpet or these ideas? The answer is very simple and is contained in the popular saying “SWR makes you stupid”. Yes, the SWR was well under 1.5:1 … BUT … even with a tested resonant linear-loaded radiating element, the overall antenna including the tuned ground circuit, was not resonant. The best impedance I could obtain was 42-j14.8 ohms. A resonant antenna is purely resistive, i.e. there is no reactive component – ideally 50+j0 ohms. Resonance results in the maximum energy transfer between the transceiver and the antenna.

LESSON LEARNED: A Ground Tuning Unit can transform a high impedance ground to a low impedance that is acceptable to a transceiver. But a transceiver cannot discriminate between a low SWR and a purely resistive load. Low SWR does not necessarily imply resonance.

Just a cotton pickin’ New York minute …

Of course an antenna doesn’t have to be resonant to radiate well – it can be adjusted to resonance by means of a “tuner” (technically an impedance matching unit). So, I added a tuner – I used my “Old Barebones” ham-made Z-match, located at the antenna end of my coax cable. That worked. It brought the antenna system into resonance, even with just a few feet of wire thrown on the ground and tuned by a GTU.

Two is too many, one is good

You heard the old saying “two is one, one is none”. Well it doesn’t apply here. Having two boxes dangling from the antenna is ungood. One box is the GTU and the other is a tuner – one too many. My next project will be to combine those two functions into a single small box. Tim KQ4TQ tried to tell me that already; I should have listened.

We’re getting close to ham hiking heaven; 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.

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 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.

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.

Be gone pesky radials!

One of the biggest bugbears of portable operations in a public space when using a vertical antenna is having to lay out radials – either on the ground, or raised. I have told the story of the dancing lady before on this blog; she performed a little jig when advised to be careful of the wires on the ground. Some of the parks I frequent are quite small and busy in the summer months, so I always have to be cautious about creating a potential hazard for other park users.

Even if I find a nice quiet area along a trail, there is often limited space in which to spread my wires. Alternatively, I may be on a mission to operate with multiple rapid deployments – drop my pack, super fast setup, operate, move on. A small vertical antenna is a very convenient way of getting on the air with minimum fuss – except for the radials.

What is the function of radials?

It doesn’t matter whether the radials are on the ground or raised, they form a counterpoise – “the other half” of an antenna. The current flowing through the radial system controls the current flowing into the radiating element. An efficient set of radials allows maximum current to flow through the whole antenna system. The current flowing in the radiating element is equal to the current flowing into the radials. More current equals more signal being radiated.

We can throw a single wire on the ground and call it a counterpoise – there seems to be a magic length of 17 feet, at least that’s what we may be led to believe from reading many online accounts. Seventeen feet may be approximately a quarter wave on 20m, but it is detuned by proximity to the ground. Is it efficient? Well, it’s better than nothing. Without that wire the operator may become the counterpoise – RF gotta go somewhere.

Transceivers can’t count radials

Let’s pretend that transceivers have eyes for a minute. When the transceiver looks at a counterpoise – whether its made of wire radials, or has a callsign – all it really “sees” is a combination of Resistance, Inductance and Capacitance (RLC). Transceivers can’t count radials – you read it here first! Resistance, Inductance and Capacitance are seen as impedance. An efficient set of radials has a low impedance to RF which allows maximum current to flow. So isn’t the current flowing into the counterpoise system really the most important factor in determining its efficiency?

Hams endlessly debate about how many radials make an efficient counterpoise. Is it 4; is it 16, or maybe 128? The debate is pointless unless other factors are also considered. The correct number is just ONE – if your antenna is erected in seawater. I want to propose another number – ZERO and, in the true spirit of scientific endeavor, I have empirical evidence to support my assertion. If an assertion cannot be verified by experiment it just ain’t so.

“I would rather have questions that can’t be answered than answers that can’t be questioned.”
― Richard Feynman

Here is the experiment

The experiment was conducted in the Ham Radio Outside the Box outdoor laboratory (my driveway). A welcome rise in temperature had melted the ice from my concrete driveway and, for once, the Sun was shining. I wanted to test a “de minimis” rapid deployment antenna that would also serve to verify my assertion about counterpoise efficiency.

The initial test was conducted with my 20m emergency wire antenna (a coil-loaded 13ft wire). Instead of radial wires I used my GTU (Ground Tuning Unit).

A GTU is a series connected L-C device. There is a sensor circuit connected to a small analog meter for observing the current passing through the device. The GTU case is a Hammond aluminum box which is electrically connected to the ground side of the GTU. The input to the GTU is a short wire connected to the shield of the coax at the antenna end.

To monitor the current in the radiating element an RF current meter was inserted into the radiator wire. The current meter is basically a GTU without the tuned circuit.

The GTU was placed directly on the concrete driveway; its aluminum box forming a capacitive connection to ground. It would have been more effective to perform the experiment on grass, but my lawn is still buried under a miniature glacier formed by another dreadful winter that isn’t over yet.

The 20m emergency antenna is nominally resonant when a counterpoise is attached so no further tuning was required. The absence of radials required the GTU to do the job of maximizing the current flow on the ground side of the antenna.

At the start of the experiment there was a small current flowing to ground. A similarly small current was observed flowing into the radiator wire (see images). The antenna analyzer recorded an SWR of 13:1.

As the GTU was tuned the ground current increased. It was observed that the current in the radiator also increased. Neither meter was capable of measuring the value of current, so the readings simply represented the relative flow of currents in the counterpoise and radiator. As the ground current peaked the antenna analyzer showed a much improved 1.79:1 SWR.

Quod Erat Demonstrandum?

So did that little semi-scientific experiment prove the point? Well kinda sorta. It established a correlation between ground side current and radiator current. But would it QSO? No, definitely not; it’s just a dumb collection of wire and electronic components – I make the QSOs eh?

Next step – hook up a radio

This is the bit where I boldy went on to risk a radio in pursuance of scientific inquiry. First, the antenna was replaced with my “tactical” 9.5ft whip wearing its finest top hat. The whip was mounted on a small tripod out on the driveway. Even with a googol (10e100) of radials this antenna would not be resonant on the 20m band. That called for deployment of my QROp L-match tuner. The radio called into service for the experiment was my old Yaesu FT-897 set for a blistering 20 watts. Since the antenna is a compromised short vertical my QRP radios were granted liberty for the day. A little muscle was called for to ensure a decent signal could be launched up to the edge of space to pound the ionosphere.

The L-match was adjusted for resonance (X=0 @ 14.113MHz), a low SWR reading on the radio, then the GTU was adjusted to max out the ground current, which lowered the SWR reading on the radio even further. Everything was ready for launch but countdown was paused for one further refinement.

A large plate for pizza?

A GTU is usually used in combination with a capacitance plate laying on the ground. The GTU body is itself a very small capacitance plate, but maybe a larger plate would enhance the ground side current flow. A quick hunt around the Ham Radio Outside the Box HQ turned up a number of options. One of the options was an old pizza pan. It worked – i.e. it raised the ground current a little, but I really couldn’t see carrying a disgusting retired old pizza pan around as part of my portable ops kit. A little further searching resulted in a small piece of what looked like chicken wire. It looked much nicer and it worked even better than the pizza pan.

The final setup – will it QSO?

Do I have to say it again? I make the QSOs not the dumb bits of wire. Well, could I make some contacts with this ZERO radial short vertical antenna system? Here is a picture of the setup.

Once again, a concrete driveway is not the best test of a GTU-based zero radial counterpoise system. The glacial layer of frozen, compressed snow on my lawn may not melt for another few weeks so one has to just make do with whatever nature allows.

I scanned the bands seeking somebody calling CQ and found a station in Connecticut doing a POTA activation. Grabbing my CWMorse paddle key I threw out my callsign and waited to hear if he heard me. Connecticut might be a little close to my QTH in southern Ontario for a vertical antenna with low angle radiation. Anyway, he heard me and sent me a 539 report. I responded with a 579. Contact was made.

A popular mantra among hams is “one is none and two is one” so I figured another contact would hammer a nail in it and seal the proof.

A little more search and pounce revealed another POTA activator in Virginia. Still quite close but my contact there earned my modest setup a 579 report.

Both those contacts were on 20m and I wondered whether another band would also work. I tuned up on 15m but the band was frantically busy with high speed CW traffic and I didn’t want to slow anybody down with my low power into an experimental antenna so I pulled the plug.

So there we have it. A very simple, rapid deployment field portable vertical antenna with zero radials. Now how am I going to make the ladies dance?

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 20-minute QRP End-Fed Half-Wave antenna coupler

It was almost time to make lunch but I had an idea that just wouldn’t wait. I figured I had 20 minutes to zip down to the basement shack/development lab and throw a simple circuit together on the workbench. I had been re-reading (for the 1000th time) AA5TB’s website about using a parallel tuned circuit to transform the high impedance of an End-Fed Half-Wave antenna down to 50 ohms. I had built a QRO version already but now I need a QRP version.

Why use a parallel tuned circuit coupler?

The objective was to avoid the use of very high impedance ratio transformers (e.g. 49:1). These transformers have received heavy criticism in online forums for numerous reasons that I won’t go into here. An alternative that is often considered to be the best option is an L-network. According to Steve AA5TB, an L-network provides better bandwidth but less feedline isolation.

I do have a QRP tunable L-network coupler on the drawing board. It will use series toroidal inductors where each inductance can be shorted out using a toggle switch. A broad range of inductance values will be selectable in binary fashion by opening and closing the toggle switches. A polyvaricon will provide variable capacitance. It’s a bit of a complicated and slow arrangement compared to the tuned circuit coupler where the only adjustment needed is the variable capacitance. So back to AA5TB’s design.

In a rush (I was hungry) I dived into my component and junque drawers, found a polyvaricon with a range of about 16-160pF, then a 2.7Kohm resistor and a BNC jack. But I still needed a coil. I have wound many coils over the years and they fill the graveyard drawer in my shack closet. I picked up one that looked like it might do the job, even though it’s a scrappy, ugly beast. When I built it I used a small cutoff of the kind of plastic board that realtors use for their “For Sale” signs. I wound 19 turns of thin solid core telephone wire around it. The winding measured 4 microhenries on my Almost All Digital Electronics L/C meter IIB.

The coil still needed a secondary winding so I wound 3 turns of the same wire over the center of the primary and connected the ends to the BNC jack. The primary winding and the 2.7Kohm resistor (simulating the impedance of the EFHW) were connected in parallel with the polyvaricon. I didn’t really expect this rushed, kluge matching circuit to work but it was a first step. I could improve the coil later once I had the initial measurements.

I love it when a project just works!

I hooked the ugly bench project up to my RigExpert AA-55 Zoom antenna analyzer and performed a quick SWR measurement on 40m, 30m, 20m, 17m, 15m, 12m and 10m. On each band the SWR could be adjusted to 1.5:1 or less. The polyvaricon does not allow very fine adjustment so tuning is a little touchy. Feeling lucky I also checked 80m – well maybe that was over-optimistic, so no joy there.

Next, I checked for resonance on each band by looking at the R and X measurements on the analyzer. Sure enough I could get resonance (i.e. X=0) on 40m, 30m and 20m. I could not tune X down to zero on the higher bands but came pretty close.

N.B. I am not implying that a single end-fed wire can be used on all bands from 40-10m using this coupler. An EFHW antenna may be tunable on multiple bands but its radiation pattern becomes distorted on its 3rd and higher harmonics. Low SWR does not indicate the antenna is useful on other than its fundamental frequency and its 2nd harmonic.

Gone to the dogs

I have placed an order for quite a lot of toroid cores from Kits and Parts. When my order makes its way through the United States Postal Service and over the border, Canada Post will take charge of it and load it onto a dog sled. It will then be hauled through the frozen barren tundra, crossing multiple time zones and finally end up at my door. No doubt the “postie” will ring my bell and seek payment of further taxes before handing over the package. When that happy day arrives – assuming the dog sled isn’t ambushed by hungry polar bears en route – I will replace the coil with a much nicer one wound on a type-2 powdered iron toroid.

Times are hard, so I’m a scavenger

It would be nice if I could find another polyvaricon to wire in parallel with the main one. A lower capacitance device would allow me to make both coarse and fine tuning adjustments. I tear apart old AM/FM radios to scavenge the components so there may be just the part I need sitting in the junque drawer already.

And, of course, the project will get a nice enclosure to make it look nice and protect it against the bumps and grinds it will incur during my back country ham radio missions.

Finally, when the second consecutive Arctic weather season is finally over and I can get outside without wearing parka, mukluks and snowshoes, I will hook up various wires to what I hope will be the finished product. I have prepared a 40m half-wave wire already. It has links for 30m and 20m so it can be used on its fundamental frequency on each of those three bands. And, of course, a 0.05 wavelength counterpoise too.

How to look simply radiant

If the counterpoise is omitted the antenna may still “tune” but the coax becomes the counterpoise and will radiate. Since a lot of portable operators, like myself, like to directly connect the coupler to the radio (or via a very short coax) the operator becomes the counterpoise and will radiate. That thought is perhaps the ultimate endorsement for QRP!

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 #Counterpoise #OutdoorOps #Portable

Great ideas from Ham Radio Outside the Box subscribers

1. QRV: An interesting iOS/Mac app for hams from Adam K2CAT who writes:

I developed QRV to be the ham app that I always wanted. There are a lot of great tools for amateur operators: QRZ, HamQSL solar conditions, PSKReporter, and more; they just were scattered and some are not mobile friendly. My goal was to consolidate everything into a single app for Apple users.

Some of the highlight features are: live spots of your grid, callsign lookup with QRZ integration for QSO info, band plans for the US, CA, and UK (more coming in 2026), lots of reference pages and calculators. My favorite calculator for POTA ops: how long will your battery last when out in the field, and what size solar panel do you need to break even?

I do have to charge for the live spots feature, but users get a significant grace period to see if it provides them real value. After emailing with the owner of PSKReporter to get some help, I decided that the most responsible path was to run my own server that ingested spots as they came in, then filter and serve the spots to my users. This greatly reduces the load on PSKReporter and ensures that I’m acting as a good community member.

Screenshots:

Unfortunately, here in the Ham Radio Outside the Box shack, Linux and Android are the operating systems in use so I haven’t been able to test Adam’s app myself. If you would like to try it out – remember Adam offers a “significant grace period” – you can download it from the Apple Store. If you do download and install it please consider leaving a comment with your thoughts down below.

2. Bruce AA1AR’s clever idea for vertical antenna radials.

A lot of attention has been given to using Faraday cloth for a ground plane recently. Either one big sheet underneath an antenna, or a set of strips forming a cross shape replacing wire radials. When Bruce wrote to Ham Radio Outside the Box to suggest an innovative alternative I was immediately interested. Bruce suggested using copper mesh – a product created for keeping rodents out from where they are not wanted. The mesh comes on a roll, 5-inches wide by 30 feet long. It can be purchased from Amazon and is very inexpensive. Note that this is NOT an affiliate link and Ham Radio Outside the Box does not endorse, or benefit from, any purchase made through this link.

Bruce tells me he has successfully used copper mesh with his own antenna; he suggests a length of 8.5 feet is sufficient to give a nice, low SWR on 20m. He mentioned that the product rolls out nicely either on the ground, or even on snow, and dries quickly.

In the past I have tried aluminum duct tape for building radials. It works, but the glue side of the tape I used is non-conductive so attempting to create, for example, crossed radials requires some other means of interconnecting the sections. And, of course, it cannot be soldered with regular leaded or lead-free solder.

A 5-inch wide copper mesh radial might even provide better bandwidth than a thin wire which complements its potential benefits. As Bruce suggested, it could also be used for raised radials – like those in a POTA PERformer. How about even using it as the radiating element too? It could be hung from a support pole – maybe not too stealthy, but the bandwidth improvement might be worth it.

I will be adding this product to my next Amazon order and – when our infernal wild winter weather gives us a break (in about another 3 months) – I might get a chance to check it out. If you try copper mesh radials before I get a chance to do so maybe consider leaving your impressions as a comment here.

My sincere thanks go to Adam K2CAT and Bruce AA1AR for sharing these ideas with Ham Radio Outside the Box. This is not a commercial blog; these ideas are shared with our visitors and subscribers as a service to fellow amateur radio operators. If you find these products useful tell Adam and Bruce all about your experiences. You can also leave your reactions as a comment below this post.

Please note that comments posted on this blog are PUBLIC. If you prefer to make private, confidential comments please use email instead. My email is good on QRZ.com.

VK2AAF commented on Bruce’s coper mesh idea: Any highly conductive ground plane will improve the radiation from your antenna. VSWR is not indicative of radiation resistance. On HF, 5-8 wire radials will behave similarly to a full circular mesh ground plane of similar size. You can confirm this by modelling with EZNEC or MMANA-GAL. https://rsgb.org/main/blog/publications/books-extra/2025/04/09/introduction-to-antenna-modelling/

An invitation to share

If you have any interesting ideas or have made a new software or hardware product you would like to share please email me the details, or send a sample for review here on the blog. My contact details are on QRZ.com. Ham Radio Outside the Box has a growing list of direct subscribers and selected posts are reproduced in many countries so a review here may reach a lot of amateur radio operators who may be interested in your product.

Thank you and welcome new subscribers

A big thank you to all the new subscribers to Ham Radio Outside the Box over the holiday period. As I have repeatedly stated in the past, this is not a commercial blog. This is my hobby, not a business. Any links provided are NOT affiliate links. Motivation for the effort that goes into these posts is the knowledge that other hams – all around the world – find the content interesting and hopefully will join in the conversation by leaving 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.

#AmateurRadio #Antennas #Counterpoise

A Year End Compendium of Outside the Box Antenna Ideas

We have reached the end of another year of crazy ideas here at Ham Radio Outside the Box and a repeat of last year’s severe winter has gotten underway in southern Ontario. The daily temperature high remains well below freezing and the ground is buried under a thick blanket of snow already. I have tried to “Keep Warm and Carry On” with more off-the-wall outdoor antenna experiments but succumbed to the biting wind and had to retreat to the warmth of the shack.

Here in the nice toasty warmth of my basement “Comms Room” I am surrounded by radio equipment, electronic gizmos, tools and almost enough wire to lay a new transatlantic cable. I also have computers. One of the computers runs the incredible HamClock program giving me instant access to updated solar propagation conditions, the current location of the International Space Station and real time data on the International HF beacon project.

Another computer is the one on which I am typing this post now. I recently realized that I have written so many posts related to field portable antennas I have built and tried that it would be a useful exercise to re-read them all. Heck, I surprised myself with some of the ideas that were posted and forgotten, but will now be resurrected. So, to end the year, I have composed a compendium of 35 of those posts – old and not-so-old – as a reference for readers to explore. I hope you may find some useful information for your own deployments.

I should stress that these are not all tried and tested designs. Some have worked so well I intend to keep them in my hambag for field portable radio operations. Others … well they were useful learning opportunities. Even if you only pick up a couple of tips such as the simplest, quick release method of attaching an antenna wire to the top of a pole the read will be worth your time.

NB: If you find any of these posts particularly interesting you can use the “Print” function on your computer and select “Save to PDF” or “Print to file” to keep a local copy.

ZZZZZ … ZZZZ … ZZZ

Ham Radio Outside the Box will now go into hibernation until the new year. Until then my best wishes go out to all in the hope that you will enjoy whatever religious or secular festival you celebrate at this time of year. Stay out of the cold!

https://hamradiooutsidethebox.ca/2025/11/04/a-simple-fix-for-my-broken-telescopic-whip/

https://hamradiooutsidethebox.ca/2025/08/29/two-resonant-simple-wire-antennas-for-pota/

https://hamradiooutsidethebox.ca/2025/09/23/a-simple-low-profile-multiband-antenna-for-pota/

https://hamradiooutsidethebox.ca/2025/08/05/rapid-deployment-field-expedient-random-wire-antenna-ideas/

https://hamradiooutsidethebox.ca/2025/07/23/does-an-antenna-top-hat-really-work/

https://hamradiooutsidethebox.ca/2025/07/11/an-outside-the-box-version-of-the-delta-loop-antenna/

https://hamradiooutsidethebox.ca/2025/05/21/reviving-a-webster-band-spanner-a-1950s-manual-screwdriver-antenna/

https://hamradiooutsidethebox.ca/2022/08/15/vertical-antenna-redesigned/

https://hamradiooutsidethebox.ca/2022/07/30/no-antenna-no-problem/

https://hamradiooutsidethebox.ca/2022/06/21/80m-band-antenna-fits-into-just-1-square-foot/

https://hamradiooutsidethebox.ca/2021/12/17/an-easy-t2lt-portable-antenna/

https://hamradiooutsidethebox.ca/2021/11/08/a-portable-vertical-antenna/

https://hamradiooutsidethebox.ca/2021/09/13/a-most-unusual-antenna/

https://hamradiooutsidethebox.ca/2025/05/14/matching-an-efhw-antenna-a-third-way/

https://hamradiooutsidethebox.ca/2025/04/23/ssefhw-another-shortened-end-fed-half-wave-antenna-for-20m/

https://hamradiooutsidethebox.ca/2025/03/19/a-simple-antenna-that-is-omnidirectional-directional-and-nvis/

https://hamradiooutsidethebox.ca/2025/03/05/a-quick-and-easy-qrp-emergency-field-antenna/

https://hamradiooutsidethebox.ca/2025/01/16/a-top-loaded-end-fed-half-wave-antenna-for-20m/

https://hamradiooutsidethebox.ca/2024/12/12/a-clefhw-antenna/

https://hamradiooutsidethebox.ca/2024/11/13/antenna-height-matters-true-or-false/

https://hamradiooutsidethebox.ca/2024/10/09/the-titanic-40m-field-expedient-backpack-portable-antenna/

https://hamradiooutsidethebox.ca/2024/08/16/how-does-the-speaker-wire-no-counterpoise-antenna-work/

https://hamradiooutsidethebox.ca/2024/07/18/a-neat-trick-with-a-20m-efhw-wire-antenna/

https://hamradiooutsidethebox.ca/2024/03/13/an-improved-self-supporting-low-footprint-field-expedient-antenna-for-20m/

https://hamradiooutsidethebox.ca/2024/03/06/antennas-a-riddle-wrapped-in-a-mystery-inside-an-enigma/

https://hamradiooutsidethebox.ca/2024/02/14/a-most-unusual-vertical-antenna-for-20m/

https://hamradiooutsidethebox.ca/2023/12/06/a-simpler-field-expedient-rybakov-antenna-for-winter/

https://hamradiooutsidethebox.ca/2023/11/05/an-upside-down-antenna/

https://hamradiooutsidethebox.ca/2023/10/19/using-a-municipal-flagpole-for-an-antenna-fine-business/

https://hamradiooutsidethebox.ca/2023/02/15/the-vp2e-a-strange-but-proven-antenna/

https://hamradiooutsidethebox.ca/2023/02/09/what-in-heavens-name-is-a-rybakov-antenna/

https://hamradiooutsidethebox.ca/2023/01/14/a-magic-ground-mobile-antenna/

https://hamradiooutsidethebox.ca/2025/01/23/an-off-center-fed-sleeve-dipole/

https://hamradiooutsidethebox.ca/2024/07/12/cutting-my-losses/

https://hamradiooutsidethebox.ca/2023/10/24/an-itsy-bitsy-teeny-weeny-upside-down-hf-whip/

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 #cw #outdoorOps #portable #pota

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

4:1 Balun or 4:1 Unun – how to choose?

Perhaps one of the greatest confusions in the hobby of ham radio is wrapped around the subject of baluns and ununs. What are they, where should they be used and what do they do?

At Ham Radio Outside the Box several antennas that need a 4:1 impedance matching device have been described. Since I had a handy-dandy 4:1 Guanella current balun in the drawer I figured it would get the job done. I applied it to my Rybakov antenna and it worked fine business. I applied it to my Simple, Low Profile, Multiband Antenna and it also worked.

In theory a 4:1 Guanella current balun (properly wound on 2 cores) would also attenuate common mode current and avoid the necessity to add a separate common mode current choke. Like I said – in theory! To be honest, I didn’t experience any common mode current issues using this device. But then I read an article written by Joeri Van Dooren, ON6URE that explained why using a Guanella 4:1 balun is often not a good idea. The reason is quite obvious once it has been explained. If it used with a vertical random length antenna – like a Rybakov – it expects to find balance where there is none. It struggles to do its job and creates a risk of core saturation or overheating. Overheating you say? Maybe that’s another one of the benefits of being a QRP or low power operator, it ain’t gonna happen – at least it’s very unlikely.

What is a Balun?

A balun can be described as a device used to match a balanced antenna to an unbalanced transmission line. Its name derives from BALanced to UNbalanced.

The accompanying schematic diagram here shows an example of a 4:1 balun. This device will match an antenna with an impedance of 200 ohms to coax with a characteristic impedance of 50 ohms. To further complicate matters, the diagram shows a voltage balun, also known as a Ruthroff balun.

It has two separate windings on the same core. The two windings are “bifilar” meaning they are wound together, side by side. Unlike the 4:1 Guanella current balun, there is no expectation that a Ruthroff balun will attenuate common mode current. A separate common mode current choke is needed.

Note that the balun has no ground on the antenna side. The two arms of the balun are balanced. The Ruthroff balun forces equal and opposite voltages on each side of the antenna. A Guanella balun, on the other hand, forces equal currents on each side of the antenna. If we were to need a device to match an antenna that is unbalanced – such as a vertical – we would need a different device called an unun.

What is an Unun?

An Unun can be described as a device used to match an unbalanced antenna to an unbalanced transmission line. Its name derives from UNbalanced to UNbalanced.

The schematic shows how it is wired. A 4:1 unun is shown but it could also be built as a 9:1 by adding a third winding creating a trifilar construction (i.e. 3 wires wound together, side by side).

Note that the configuration is quite different to the 4:1 balun. Instead of the two arms of the antenna being balanced, one side is now at ground potential. This suits a vertical antenna with a system of ground radials.

Isn’t a Balun just a fangle-tangled Unun?

Strangely, considering their different functions, there are a lot of similarities. If we wanted to convert one to the other, a few minutes spent with a soldering iron would get the job done.

Referring to the accompanying diagrams here we can see there are three main components:

• The antenna connections – either balanced or with one side grounded
• The bifilar (or trifilar in the case of a 9:1 unun) inductor wound on a toroidal core
• The coax connector for connection to our transceiver

If we follow the next two diagrams showing how to assemble an Unun or a Balun we can see the similarities in the two devices.

How to choose the correct device?

Once I had made the decision to “do it right” and replace my Guanella current balun with a Ruthroff voltage device, I had to choose between a balun and an unun.

Since I was out of spare toroid cores in my shack component drawers the Guanella balun had to be sacrificed. It had given good service but, in the interest of adhering to good RF physics, it was laid to rest.

The two cores each had a bifilar winding that was identical so I decided to build both a balun and an unun. My intention was to evaluate what would happen if I tried each one. The antenna on which the trials were performed was my wire version of KJ6ER’s Challenger antenna.

The science was telling me that the unun was the correct choice. Call me ‘ornery but I prefer to find out for myself. I like to test the alternatives in the big outdoor lab I call my backyard.

With both devices in my pocket I erected the antenna – clearly not a balanced antenna because the vertical wire is 22 feet long and the counterpoise is only 5.5 feet long with its far end laying on the, as yet, snowless lawn. So, first up was the balun. I didn’t expect this to work at all, but I did want to observe what the result would be. Would it be smoke, rising up into the sky, signaling my ignorant disregard for what the physics was clearly telling me?

Gadzooks!

To minimize the size of any potential mushroom cloud arising from my scientific folly, I chose a very low level of RF – you could call it “QRPpp” perhaps. The source was my antenna analyzer. To my astonishment, hitting the big button that sent milliwatts of RF coursing through the balun into the antenna produced no fireworks. Instead, with a little minor adjustment of the length of the radiator and counterpoise, the antenna analyzer showed a surprisingly good SWR. Hitting another button on the analyzer showed the antenna was resonant just below the 20m band. I like to operate CW near the bottom of the band so that would be just fine.

Next up was the scientifically anointed device, the Chosen One, the device whose destiny was ordained to become part of my field kit – the Unun. Of course it worked too.

Now let’s summarize the experimental results here. The Guanella 4:1 current balun worked – but it shouldn’t have. The Ruthroff 4:1 balun worked – but it shouldn’t have. The Ruthroff 4:1 unun worked as expected. I earned my physics degree a long, long time ago but studying for it gave me a lifelong habit of following the scientific method – as verified by my own experiments.

Of course a low SWR tells us nothing about the efficiency of the antenna system. It only indicates that it won’t drive the magic smoke out of our transceiver. The wrong matching device may result in less of our transmitted signal being radiated.

So the end of the story is I will be using the unun, confident that it is backed up by antenna physics – and my own, white lab coat wearing independent verification!

The final image shows the unun mounted on my wire Challenger antenna during its backyard trial. The larger toroid is a common mode current choke. The small one is the unun.

Note I used an FT140-43 ferrite toroid core even though many sources recommend a powdered iron core such as type 2 material. Type 43 ferrite material is not the optimum mix for the 20m band and up but it is what I had. I may have wound too many turns on the core, risking core saturation. When I tidy up the construction I may reduce the number of turns from 10 down to 8.

NB: I have been unable to find a source for type-2 powdered iron toroids. Can anybody tell me where to buy them, preferably in North America?

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 #counterpoise #cw #portable

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

A Road Trip with the POTA Tripod Antenna – with surprises!

A spell of warm, sunny weather and a chance to get out to see the fall colors in early October prompted my wife and I to go on a road trip up to Ontario’s Muskoka region and on to the fabulous Algonquin Park. The park is Canada’s largest and oldest and is the home to thousands of black bears, as well as moose, deer and wolves. Sadly, all the wildlife hid from us on this trip.

Propagation conditions remained uncertain at best, so the third passenger on the truck journey north was my Yaesu FT-891 QROp rig set to an unusually high 35 watts. And the antenna of choice was the 13ft tall vertical based on a tripod that has been the subject of recent posts. Once again, this antenna got the job done, and even revealed some surprises.

Inside Algonquin Park, at Mew Lake campground, I set up to check band conditions. As usual, I started by hunting other activators to see what kind of signal reports I would receive. Bad propagation numbers do not always result in difficulty making contacts. I had considered just leaving the radio in the truck and enjoying the sunshine on the quiet beach by the lake, but after settling into my camp chair I grew restless and within a few minutes I was calling activators and making QSOs.

There are two ways to perform an activation

Calling CQ is the best way; it makes an activator the target for eager hunters and often results in pile-ups. If you know how to handle a pile-up you can complete an activation in short order. But, when conditions are not so good, calling CQ repeatedly and getting no responses can be disheartening. Once I have spotted myself on the POTA website I like to complete at least a basic 10 QSO activation even if it takes a while. Trouble is, when time is limited, other priorities may take precedence and that can result in a busted activation and disappointment. Of course, it is still fun to get on the air out in the Big Blue Sky Shack, but there is another way to have fun and do an activation.

On several occasions I have taken a more relaxed approach and simply hunted other activators until I have completed 10 or more QSOs. This method is a little more difficult because it is necessary to compete with other hunters for each QSO. The advantage, as I see it, is there is no compulsion to complete the minimum 10 QSOs if conditions are bad. I can stop at any point and just consider it a fun day in the park. If I make my 10 contacts I file my logs with POTA and every QSO is automatically a “P2P” (Park-to-Park).

“Hunted activations” are my backup method when time is limited and conditions are bad. On that day in Algonquin Park I chose this method and ended up short of the required minimum of 10 contacts for a valid activation. We had two more days in this mini fall vacation and better conditions were ahead of us, but that day the park had other attractions we wanted to see.

Our overnight accommodation was a “bricks and mortar tent” with breakfast included. Many years ago I canoed into the backcountry inside Algonquin Park every summer and slept in a tent at the edge of several of the park’s many lakes. It was refreshing to get away from the crowds and enjoy the solitude of nature out in the wilderness. In almost complete darkness, at 2:00 AM one night, that solitude was interrupted by a very close encounter with a very large black bear. Fortunately the bear didn’t have me on his supper menu that night. After ransacking the campsite and attempting to claw the food bag down from a tree, it moved on in search of easier meals.

“CB or Ham?” inquired the lady with the Whippet

Leaving the safe, solid, bear-proof accommodation in a nearby town the next morning we entered one of our favorites among Ontario’s parks where we would spend the entire day, with plenty of time for radio. The QTH for the day was Arrowhead Lake Provincial Park (CA-0140), a park I have activated before so I already knew the best location for setting up the radio.

The operating site was at the far end of the lake beside the dog beach. The accompanying picture shows my relaxed operating position. We spent several hours at the dog beach and that included meeting and greeting several dogs (we love dogs).

A couple of ladies came by and one of them asked me: “CB or Ham?”. It is nice when I don’t have to explain ham radio to a visitor. She seemed genuinely surprised though when I explained that I was using Morse Code to contact other hams all over North America. And her pet Whippet was very excited to meet a CW operator in person.

Band conditions had improved since the previous day and the contacts were much easier to obtain. I started out hunting other activators as usual and the contacts just kept adding to my log despite the K-index sitting at an uncomfortable high of 4. The activation wasn’t as fast as if I had called CQ, but time was not pressing so I earned a complete activation, with QSOs to spare, over a period of an hour and a half. Eventually, as the area grew busier, I decided to pack up and head back to the “tent”.

Smoke on the Wahta

The next day we had to head back home, but the route took us via another of my favorite parks – Torrance Barrens Nature Reserve (CA-1669). The “Barrens” is a couple of hours relaxed drive south of Algonquin and the trip took us through the Wahta Mohawk First Nation reserve where tax-free bargains can be found on gasoline and smoking products. My wife and I are not smokers but we are always amused by a sign along the road advertising “Smoke on the Wahta”. Readers who grew up in the same era that we did may recognize the reference to a popular song from the 1970s.

Activating The Barrens

The Barrens is located at the south end of Muskoka and is a popular haunt for astronomers. The topography is characterized by the exposed ancient rock at the southern end of the Canadian Shield.

I set up my station on the bare rock near a small lake and once again started hunting other activators to test band conditions. After only four QSOs I switched to CQ mode. Things were going well and in just 27 minutes I completed 15 QSOs. Then suddenly, as I was finishing a QSO with KC5F in North Carolina, my radio shut down. I powered the radio back up again and managed to finish the contact before the radio shut down once again. I checked the voltage of my Bioenno Lithium Iron Phosphate battery and saw the reason why – the voltage was 11.5 volts. I hadn’t recharged it during the trip and it had given up on me. Lithium batteries maintain a fairly constant voltage until they are almost fully discharged. Neglecting to keep them well charged comes with surprises – like a forced QRT.

But that wasn’t the only surprise of the day. As I was packing up my station I noticed that I hadn’t fully erected the antenna. The top tube section of the tripod, which forms part of the radiating element, was not extended. Despite this error the antenna performed very well. I was pleasantly surprised and pleased with the results for the day.

A final word about the radials

I had originally intended to use the linked, tuned radials from my wire version of the POTA PERformer antenna, but there was a problem. Those two raised radials contain links for 17m and 15m. The link for 17m is at 13ft along the 17ft radial wires and the link for the 15m band is at 11ft. Now here’s the rub (as Shakespeare would have said), the radiating element is also 13ft long. Since there is a 4:1 impedance transformer in the feedline the impedance on 17m was out of the tuning range of my LDG Z-11 Pro antenna matching unit.

The solution was to use a set of four 13ft radials laid partly on the ground. Now the LDG Z-11 can easily find a match on all the bands from 20m to 10m. Is 4 radials enough? The feedpoint of the antenna is raised about 3ft/1m above ground so maybe less ground plane is required. Setting antenna physics aside, the prime rule for temporary field expedient antennas is to use the antenna you have and just get on the air.

Winter is fast approaching

Up here in the Great White North life contains 3 absolute certainties: death, taxes and snow! The time for relaxed operating in the sunshine beside a lake is nearly over; now it’s time to get back to planning antennas for operating while shivering in my truck!

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 #Counterpoise #CW #OutdoorOps #Portable #POTA

Does an antenna top hat really work?

There are several ways to shorten a vertical whip antenna, for example, a loading coil, linear loading (folding back all or part of the radiating element) and one that has intrigued me for quite a while – a capacitance hat, also known as a top hat.

A top hat (shown in this image) is a series of conductors erected horizontally, and connected to, the radiating element of a vertical whip antenna.

Top hats provide capacitance with respect to ground and are used for two main reasons:

1. To shorten the required physical length of a vertical antenna
2. To raise the maximum current point higher up the antenna

One significant disadvantage of using a top hat is that it adds weight to the top of the antenna. That may not be a problem for a fixed installation where a thick, rigid vertical element can be used. But for field expedient portable operations using, for example, a telescoping whip it can be a very bad idea indeed. Let me explain why.

I recently purchased a top hat designed for a PAC-12 antenna from AliExpress. I attached it to the top of my 18.5ft whip obtained from the same source. The top of the whip waved around in the air and clearly was not going to be a practical arrangement. These Chinese whips are made much lighter than similar products from other sources (e.g. MFJ-1979 which I also own) and consequently are not as strong. To be fair, the manufacturer would probably advise against abusing their lightweight whips in the manner of my little experiment. I guess I overstressed the thin top sections of the whip which subsequently parted company from the lower sections. I attempted a repair which wasn’t successful, so I am now the owner of a shorter whip which may see service in a future antenna experiment.

I own another whip – a “tactical”, military style whip that is 9.5ft long. It is made from several sections of fairly rigid tube held together by shock cord. Although the sections taper toward the top, the uppermost section is still quite strong. When the top hat was attached to this whip, the whip bowed very slightly but appeared to be quite able to support the weight.

The AliExpress top hat arrived in a surprisingly small package. It comprises a central hub secured to the whip by a small hex screw and four tiny telescoping whips that expand to 12 inches long. When fully assembled the top hat has a diameter of about 24 inches.

How did it perform?

I was a little skeptical about this arrangement. Could a small capacitance hat compensate for the short (9.5 feet) length of my whip on the 20m band? It was a shot in the dark and the short answer is no it could not. But that isn’t to say the top hat totally failed in its mission. In fact, it did make a difference as will be explained in a minute.

A small top hat alone cannot easily compensate for a very short antenna. There are ways to improve the top hat – such as adding a perimeter wire linking the tips of all the horizontal conductors, or even making the horizontal conductors longer. For rapid deployment in the field the perimeter wire is tricky to implement. The stock AliExpress top hat can be assembled and installed in about a minute; adding a perimeter wire makes the assembly more complicated – especially when backpacking the whole station into the bush.

Making the top hat’s horizontal conductors longer introduces another complication. These conductors carry a very small current; if they are made much longer the current will increase (e.g. as in a Marconi T-Antenna) and they will radiate.

A much simpler, but less efficient, idea is to combine the top hat with a loading coil, and that is the route I took. I revived an old ham-made adjustable loading coil I had built for another project a few years ago. The loading coil had to be placed at the bottom of the whip for mechanical stability. Since this is also the maximum current point the coil will introduce i^2R loss, but compromises have to be made.

The end result was a base loaded 9.5ft whip with a 24-inch capacitance hat at the top of the whip. The adjustable coil enabled the antenna to work on 20m, 30m and 40m by simply adjusting the coil slider. Four 13ft radials were laid orthogonally on the ground at the base of the whip as a counterpoise.

Step One

First, the top hat was left to one side and the coil slider was adjusted to find a match on each of the three bands of interest. I used my RigExpert antenna analyzer to measure the results, then when a match on each band was found, my trail-hardened Yaesu FT-891 was deployed and verified the results.

Step Two

The top hat was then installed and the tests repeated. Now the coil setting for each band was quite significantly different. The required inductance was reduced which means the i^2R loss was also reduced – that was encouraging. So the shortening effect of the top hat was verified, but what about the point of maximum current; was that raised too?

I attempted to model the antenna using EZNEC. I have to admit that I have only a very limited knowledge of antenna modeling, so I cheated a little. I modeled a full-size quarter-wave whip for 20m and looked at the antenna currents. Then I added the top hat to the model and looked at the antenna currents again. Would the top hat raise the maximum current sufficiently to get it above the loading coil and thereby reduce losses in the coil? The following chart shows the results.

Bingo! (but no big prize)

As we can see by looking at the chart, the top hat does indeed raise the maximum current point. The model divided the whip into 50 segments and the current maximum is raised from segment 1 with no top hat, to segment 10 with a top hat. That means the point of maximum radiated energy is raised to a point 20% up from the bottom of the whip. Hallelujah.

But just a cotton-pickin’ minute, the actual maximum current changes very little between the first and tenth segment so did we actually achieve anything useful? Well yes we did actually. If we look at segment 50 on the chart we can see that without the top hat the current drops to zero at the top of the whip. On the other hand, with the top hat installed, there is still significant RF current all the way up the whip – so the entire whip is contributing to radiation!

Did the maximum current point clear the loading coil?

I won’t win a Nobel prize for this bit of non-science, but here is my analysis. If the whip is 9.5ft long, the loading coil is compensating for most of the other 7.5ft of a nominal 17ft whip. 20% of 17ft is 3.4ft so that falls well within the loading coil. Hence no, the current maximum will still be in the loading coil. If any reader can convert the above into real science I would welcome your input.

This was interesting experiment and convinced me that top hats really do improve a vertical whip antenna. Will this arrangement actually be used in my field portable operations? Yes, for sure; the top hat has the effect of “decompromising” (to some extent) a compromise antenna. When the prime mission is to carry a rapid deployment, field expedient portable antenna into the bush, remote from roads and parking lots, this antenna has earned in its place in my backpack.

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 #Counterpoise #Ground #OutdoorOps #Portable

Testing and modifying the “POTA PERformer” antenna

What is the POTA PERformer? Greg Mihran KJ6ER has introduced us to an antenna that he calls the “POTA PERformer”. The capitalized PER in its name is an abbreviation for “Portable, Elevated, Resonant”. But what is it really? The POTA PERformer is an adjustable elevated vertical radiating whip with two adjustable elevated radials. In concept there is nothing really new about it, but the unique implementation devised by KJ6ER is quite interesting.

Get up off the ground

Most hams will be aware that a quarter wave vertical antenna, mounted on the ground, requires an extensive system of radials to be efficient. I have successfully used such an arrangement with as little as four radials during a POTA activation out in the Big Blue Sky Shack. But, as they say, even a poor antenna will get you contacts when conditions are right. Some recommend as many as 120 radials although anything over 16 provides very little further improvement. In a portable situation laying out a lot of radials for a short-term temporary station doesn’t make a lot of sense. So what is the alternative?

Less is more

If the base of the antenna is raised above the ground, fewer radials are needed to form an effective counterpoise and make the antenna efficient. How many? KJ6ER has settled on two radials for the POTA PERformer. If the radials are arranged at 90 degrees to each other the antenna has a directional radiating pattern. But using two radials increases the footprint on the ground and that could be an important consideration if, for example, we are operating on a narrow trail. Could we get away with just one radial? I modeled a POTA PERformer using EZNEC and came up with a comparison, shown in the following table.

TABLE: 1 radial versus 2 radials

Now I’ll admit that I am no expert in computer modeling, but the results I obtained seem to differ from what KJ6ER found. In either case, whether two radials or just a single radial are used, we have a directional antenna that can be rapidly deployed in the field.

One radial or two? Now here’s a surprise!

The original POTA PERformer is a multiband antenna. It covers all the bands from 20m up to 6m with a 17ft telescopic stainless steel whip and adjustable length radials. KJ6ER suggests extending the band coverage to 30m and 40m by means of a loading coil at the base of the whip and then … surprise … combining the two radials to create one long radial wire. I suspect the 30m/40m version may lack some of the gain and efficiency of the higher band version due to the losses involved in base loading a vertical radiator. Perhaps a full length vertical wire supported by a pole, or a tree, might be better.

I have always felt there is something incongruous about using a counterpoise that is longer than the radiator. Perhaps that concern is unfounded if we consider that a raised radial wire also radiates.

Customizing the original clever idea

I have tried the POTA PERformer with both a single radial and two radials. Both versions “worked” and I made contacts. It is difficult to interpret which was better, but my own preference – for field expediency – is a single radial. The 20m, 30m and 40m bands are my preferred haunts, only for the reason that two of my QRP radios do not support the higher bands. Even though the POTA PERformer is a great idea with very positive reports from several sources on YouTube and elsewhere, it doesn’t fit well with how I like to operate. Here is why.

Please remain seated

A raised radial wire is a tuned counterpoise. Its length is important. That means band changes involve adjusting the length of the radial(s). One way of doing this is to insert a non-conducting link in the wire and move it between linked sections to set the conducting part of the counterpoise to the correct length for the band of operation. The overall length remains the same but the sections of the wire not being used are isolated from the rest of the antenna. Another way that I have tried is to use a metal measuring tape and unwind it to the correct length. Perhaps using multiple raised radials where each wire is adjusted for a different band would also work. Whatever method is used, getting out of your chair and fiddling with radials and whip lengths is a time consuming distraction. So what’s the alternative; how can you stay in your seat and change bands?

Get on the ground and spread ’em!

Sacrificing a little efficiency is required but it can be done. My own method is to spread out four radials wires in a fan pattern on the ground, facing the direction I want my signal to go. Are four ground radials enough? If the vertical element is ground-mounted then using only four radials results in efficiency loss. But, if the whip is elevated? Who knows, but it works.

Since ground radials are detuned their length is not critical. No adjustment is required whether operating on 20m, 30m or 40m. The only requirement is that there is sufficient copper on the ground to provide a good counterpoise; I use 4x13ft radials. Orienting all the radials in one particular direction does improve the signal in that direction to a small extent. How much efficiency is lost? That is very hard to quantify but the convenience factor is high.

A 17ft whip with an adjustable loading coil (bypassed for 20m) will cover all three of the bands that I need. I have also used a 9ft “tactical” whip whose fixed length sections are held together with bungee cord. This shorter whip uses a separate loading coil for each band and is usually only employed with my QROp rig (a 100 watt radio that is usually set to 20 watts or less). This radio gives the ability to transmit a little more power when needed.

“QRP when possible, QROp when needed” – Ham Radio Outside the Box

Is there any real difference between 5 watts and 20 watts? Maybe not but it does give me a nice warm feeling – especially if I get too close to the antenna while keying up.

To better understand and learn more about the POTA PERformer it is worthwhile downloading and reading Greg KJ6ER’s PDF document. It may inspire you to build one or even devise your own variant to suit your unique operating needs.

Note to Fediverse readers: the formatting of this post may be presented better on the original WordPress site. Visit: https://hamradiooutsidethebox.ca/2025/05/27/testing-the-pota-performer-antenna/

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 #Counterpoise #Ground #OutdoorOps #Portable #POTA

Reviving a Webster Band Spanner – a 1950s manual screwdriver antenna

About 20 years ago I was approached by a neighbor who, knowing that I am a ham, asked if I might be interested in looking at some of the old ham junque he had accumulated over many years. He was a fine gentleman, in his golden years, who was no longer active in the hobby. Hesitating for less than a microsecond I eagerly agreed. Among the treasures I acquired was a Signal Electric straight key. I believe it was an R48 model first introduced in 1920 when it sold for $2.80. But my prized acquisition was a Webster Band Spanner antenna.

The Band Spanner was produced in the 1950s and 1960s by the Webster company in San Francisco. It is a center-loaded manual screwdriver antenna intended for mobile operation. Unlike modern screwdriver antennas, like the popular Tarheels, that use an electric motor to make band changes, the Band Spanner has to be manually adjusted for each band by sliding the whip up and down.

Two models were produced; the A-61 and the A-62. The A-61 (that I acquired) has an extended length of 93 inches and a collapsed length of 60 inches. The longer A-62 model has an extended length of 117 inches and a collapsed length of 63 inches. Both models support the 75-40-20-15 and 10 meter bands. There is a mark on the whip indicating the mid-point of each band. I suspect the WARC bands could also be tuned although it would be necessary to locate the correct whip length by trial and error. The antenna is rated for “100 watts or more”.

The Band Spanner is constructed from a fiberglass support column with a 24-inch long internal loading coil. At the base of the whip is a circular contactor that connects with the windings of the loading coil. As the whip is raised or lowered, the contactor connects to individual exposed turns of the loading coil inside the support column. This type of continuous adjustment permits exact resonance to be achieved anywhere within a band. It is a very high Q antenna – moving the whip just one click up or down (one turn of the loading coil) makes a significant difference to the tuning.

Would the vibration of a vehicle change the tuning?

You might expect that a bumper-mounted antenna would be subjected to a lot of stress as a vehicle crashed through pot-holes and other rough ground, but there is a very tight connection between the whip and the loading coil. The connection is so tight that it requires some force to adjust the whip length and it is quite possible to skip a turn if too much force is used. The tight connection has a another positive benefit – it makes the connection point self-cleaning. There is also a locking thumb screw at the base of the whip to help secure it in place.

Stationary mobile operation

I am not a mobile HF operator; there are enough distractions already to compromise driving safety, so I prefer to use the Band Spanner as a stationary mobile antenna. For those who do intend to use it as a mobile antenna, there is the H-200 ball mount (shown in picture).

I have tried several ways of mounting the Band Spanner as a temporarily fixed position portable antenna. The manufacturer suggests using a matching section of 21 feet of RG-8/U coax and grounding the shield of the coax to the vehicle body. I did once try using such a matching section with a Band Spanner on a tripod, but it didn’t seem to improve the tuning at all. Most recently I attached my Band Spanner to my “QROp” (5-100 watts) radio set. It is a Yaesu FT-891 mounted inside a mil surplus 50-cal ammo box. The Band Spanner was connected directly to the rear of the rugged steel case. My ham-made L-match tuner was used for fine adjustment of the SWR.

Tuning was fairly easy. I set the radio to 20m and 5 watts power output. I threw a 17ft wire counterpoise on the ground behind the radio. A single wire counterpoise is not really sufficient ground for this antenna so additional inductance had to be added via the L-match. I would usually lay out at least 4 radials for a portable vertical antenna, but I was on a mission. I wanted to find out if the Band Spanner could be employed as the radiating element of a “POTA PERformer” type of antenna. Ham Radio Outside the Box will be exploring the “POTA PERformer” in more detail in an upcoming post. For now we can describe it as simply a raised quarter wave whip with raised tuned radials.

Now comes the surprise

Having tuned the antenna with one ground radial to less than 1.5:1 SWR I thought I was on a roll. Next step, I raised the radial so that it would not be detuned by contact with the ground. I now had the Band Spanner set for the 20m band, finely adjusted by means of the L-match to give a good SWR. I expected some further adjustment might be necessary with a raised 17ft counterpoise, so imagine my dismay when the radio flashed its “high SWR” warning.

The Band Spanner is intended to be used while mounted to a couple of tons of steel vehicle serving as its counterpoise. It is a very short, loaded vertical antenna with very high Q performance. A lesson I learned early in my ham career, but overlooked in this exercise, was that a short-loaded, high Q vertical whip requires a carefully tuned counterpoise – or a good ground. Simply using a raised 17ft wire isn’t good enough. I would have had to precisely trim the raised radial wire to get a good SWR. To make this even more complicated, a precisely trimmed radial wire counterpoise for each band would be required. So the mission objective to examine the Band Spanner’s suitability as a portable POTA PERformer was concluded. In future, the Band Spanner will be used with the best ground system I can erect during a temporary field installation.

Another thought …

A Band Spanner (or even better – a motorized screwdriver antenna) could possibly be used in an HOA situation. If it were ground mounted, with a good system of buried radials, it could potentially be disguised to prevent detection by the HOA hounds.

And finally …

I am not sure of the actual age of my Webster Band Spanner. They were produced in the 1950s and 1960s so I estimate it to be at least 60 and maybe as much as 75 years-old. The bumper mount has entirely lost its plating and is now a dull rust color. The fiberglass support column is equally dull and has lost its identifying markings. But, the antenna still functions as the Webster company intended all those years ago, which is more than can be said for its owner who is of the same vintage!

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 #BandSpanner #Counterpoise #Ground #OutdoorOps #Portable #POTA

EFHW matching: 49:1 Impedance Transformer or L-Network?

What is the best way to match the very high impedance of an End-Fed Half-Wave antenna to the 50 ohm impedance of a transceiver? There are various ways to do this but this week’s post is going to focus on just two – a 49:1 impedance transformer (or UNUN if you prefer) and an L-network.

We are dealing with QRP devices but the same issues arise with QRO devices. In fact some of the complexities may be exacerbated at higher power – especially core overheating.

49:1 impedance transformer

This is by far the most widely used matching device but many claim it is inefficient. I have used an “Outside the Box” winding method that I have seen described as “Fuchs style”. The primary and secondary windings are entirely separate instead of being twisted together. This method isolates the windings and is said to prevent static from traveling back down the coax to damage the transceiver. But it also requires a separate 0.05WL counterpoise connected to the bottom of the secondary winding.

Pros

• Broadband operation
• Easy to construct
• No calculations needed

Cons

• Lower efficiency claimed
• Can be used on even harmonics but the antenna is only a half-wave on its fundamental frequency
• Potential for losses due to core overheating
• Leakage flux due to poor coupling between windings
• May require capacitance across primary and/or secondary to compensate

L-network

Some claim that an L-network is more efficient than an impedance transformer. While I don’t dispute the claim I would respond “show me the math”. An L-network is usually constructed from a fixed value serial inductor and a fixed value parallel capacitor (although there are other topologies depending on the matching parameters involved). I built one using a slug-tuned variable inductor and a ceramic trimmer capacitor.

Pros

• Higher efficiency claimed
• Easy to construct
• Avoids complex issues with transformer cores and winding coupling

Cons

• Single band only
• Calculations required to establish correct values of L and C

The Ham Radio Outside the Box laboratory (a grand name for my basement workbench) has built many 49:1 impedance transformers for both QRP and QRO operation. The QRP units are deployed in backpack portable operations and the QRO units have seen service both in the field and in the home shack. Both the conventional “twisted” coupling method and separate windings have been used.

Which winding method is best?

One of the issues with 49:1 transformers is “leakage flux” which means not all of the energy in the primary winding is coupled to the secondary. The conventional winding method is to twist the first two turns of the primary and secondary together to improve coupling. The remaining turns are only coupled to the primary by the flux in the core. Furthermore, there is often a “crossover” turn to bring the far end of the secondary out on the opposite side of the core from the primary. This may further reduce the coupling efficiency.

An alternative method is to wind the secondary, without a crossover turn, around the core. The separate primary is then wound around the center of the secondary. Should the secondary be spread around the core, or closely spaced? Opinions vary on this. I now favor keeping the secondary turns closely spaced. The reason? A closely spaced secondary winding should improve inter-winding coupling and reduce leakage flux.

What about the turns ratio?

Should it be 49:1, 64:1 or …? There is an easy answer to that: just divide your antenna impedance by 50 and bingo, there’s your answer. Oh, but what is the impedance of your antenna, 2000 ohms, 2319.647 ohms, 3000 ohms? We don’t actually know and it may vary depending on how the antenna wire is erected (which for portable operators may be different every time). A ratio of 49:1 provides a good enough match to most every value of End-Fed Half-Wave (and multiples) we are likely to experience.

Or just build an L-network!

We have seen that 49:1 impedance transformers have many variables that impact efficiency. Leakage flux has been discussed so it is relevant to note that placing a small capacitor (typically 100pF) across the primary winding is recommended to somehow compensate. Conventional 49:1 transformers are wound as autotransformers, so we have a series inductor between the antenna and the radio, and a parallel capacitor. Doesn’t that sound very similar to one of the topologies of an L-network?

My initial experiments with building L-networks involved a fixed series coil and a parallel capacitance made from a short length of thin coax – like RG-174. I experienced the problem that the calculated values of L and C did not provide the best possible match to 50 ohms. I still needed a “touch-up” tuner to bring the SWR down to a safe level for my QRP Labs QMX transceiver. I realized that a field portable antenna was going to need slightly different component values depending on whether my temporary station was setup on exposed ancient bedrock, or over the moist ground at the edge of one of the Great Lakes. What I needed was an L-match “tuner”, i.e. an L-network with variable inductors and capacitors.

42 years ago …

A long, long time ago (42 years to be precise) I was a penniless SWL foraging for food in the forest – alright that’s an exaggeration, but I had a young family and couldn’t spare the cash to buy a decent shortwave receiver. A friend told me about a design in Practical Wireless magazine for a shortwave converter that would work with a regular domestic AM receiver. I had the components shipped over from the recommended UK suppliers and built the converter. It worked splendidly and I spent many happy hours listening to the busy shortwave bands. Then I became fabulously wealthy (i.e. I could at last afford shoes and to eat every day of the week), bought a real HF radio and the converter was relegated to the back of a closet.

The point of the story is that I was able to scavenge that converter for the components I needed to build an L-match for an End-Fed Half-Wave antenna. The inductor shown in the picture above is wound over an adjustable slug-type ferrite core of unknown mix. The capacitor is a ceramic trimmer with a couple of fixed ceramic capacitors in parallel to bring its value into the range that was needed. The only comment I can make on the efficiency of that unknown core is that it didn’t get hot (or even warm) after an extended period of transmitting at 5 watts. Tuning is quite sharp but I was able to get a 1.5:1 SWR from my Shortened Sloping End-Fed Half-Wave antenna (see last week’s post). I probably could have obtained an even lower SWR by adjusting the length of the high Q top section of the SSEFHW.

QSO’s?

As a recent convert to L-networks I have only made enough QSOs to be countable on fingers and toes. On the other hand, over the years, I have made thousands of QSOs with a 49:1 impedance transformer. Both the devices shown in the pictures above accompany me on every field portable outing so I have options and can compare their performance.

Does it matter, really?

Sometimes I give my head a shake and tell myself to put the physics textbooks back on the shelf and just enjoy the experience of being out in the Big Blue Sky Shack with my radio. At other times, after calling CQ ’til the cows come home and getting no responses, I ponder the question of whether my antenna is doing its job or, as sailors used to say, is idly “swinging the lead”.

What are your experiences with either impedance transformers/UNUNs or L-networks? Your opinions are very welcome either by adding a comment below, or if you prefer, by email (QRZ.com).

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 #Counterpoise #OutdoorOps #Portable #QMX

I KISSed my Antenna – Here’s Why …

Many years ago I learned about a design technique called KISS. It was an acronym for “Keep It Sweet and Simple”. Somewhere along life’s journey I started seeing the acronym change to the rather offensive “Keep It Simple Stupid” which I entirely dislike. There are many sound reasons for simplifying a design but none of them imply a lack of intelligence on the part of the designer. Designs evolve and, in the process, become very complicated to the point where the probability of failure becomes critical.

A case in point is the Saturn V rocket that first took astronauts to the Moon. If I recall correctly, the Saturn V had something like 10 million components. If each component had been designed so that it had a 1 in 10 million chance of failure, the rocket would probably have failed at every launch. The reason is straightforward – failure probabilities in a complex machine are additive.

Every mistake is a learning opportunity. The designers of early rockets were certainly not stupid, but their rockets exploded on the launchpad, or during the early phases of launch. Even when rocketry had advanced sufficiently to repeatedly land men on the Moon, terrible disasters still happened.

There is a temptation to be so focused on an objective that errors slip into the design. Reviewing my own antennas, many of which have been featured in this blog, and the feedback I have received from some very knowledgeable Ham Radio Outside the Box followers, caused me to stop and re-think my designs. Every antenna discussed here in this blog has worked, meaning I have personally made contacts with each and every one of them. But, at the same time, some of the designs had flaws caused by too narrow a focus on end objectives. So, I made a decision to adopt a KISS approach.

These are my principle objectives based on my personal interest in operating backpack portable out in the Big Blue Sky Shack:

• Rapid deployment – an antenna must be ready to transmit as quickly as possible upon arrival at an operating site.
• Field expedient – An antenna must be specifically designed and constructed for temporary field operation. This necessarily implies that efficiency is not the prime objective. A “compromise” antenna is acceptable if it works well enough to make contacts.
• A small footprint – the entire station should occupy as small a footprint as possible, keeping in mind that many operating sites are in public spaces where other people may be present.
• Ham-made, meaning I don’t buy commercial antennas. I prefer antennas I have constructed myself. It saves money and allows more scope for experimentation.
• Stealthy – the mission objective is to make contacts, not educate curious people passing by. Ham radio equipment may look suspicious to some people; better to look inconspicuous and not be noticed.
• Self-contained – the antenna must not be dependent on anything I didn’t bring with me. This includes trees, vehicles or any other kind of antenna support.
• Everything must fit in, or on, a backpack that is sufficiently lightweight to be hiked into a remote operating site, or transported using a wheeled cart.
• Ancillary equipment, any chairs, tables, shelter, spare cables, spare battery, water and food must be part of the backpack portable package.

Softly, softly, catchee monkey

The “Stealthy” objective may sound unfriendly but it is very practical, especially when working a pile-up as is often the case with POTA. If somebody stops to ask questions I give them a very simple, but polite explanation. Usually they are just curious with no particular interest in ham radio. I was set up in a local park recently and had just completed a POTA activation when an official Ontario Parks vehicle pulled up in front of me. A young park warden got out and came over to ask me what I was doing. She told me she saw my big whip antenna and wondered what it was for and seemed interested when I told her I was contacting people by radio using Morse Code. She asked me how long I had been doing this. I was tempted to reply “oh, only about a half hour” but I overcame my frivolous inner self and replied “25 years”.

And another consideration; CW ops have a stealth advantage over phone ops – our operation is silent if we wear headphones – or ear buds which look less suspicious. If they can’t hear me they are more likely to pass on by. “He must be tracking wildlife, or something, best not to disturb him”.

It’s okay to be an ambassador for the hobby, that’s what Field Day is for. If it’s a quiet day on the bands I might be happy to have a nice conversation with a passer-by, but when the ether is overflowing with chasers and hunters the focus is on the mission’s prime directive.

We gotta get out of this place

There are many reasons for wanting a rapidly deployable portable rig. Out in the great outdoors the weather can change suddenly necessitating a fast teardown of antenna and radio. In a public space – such as a park – other people may gather in close proximity to our operation creating a disturbance or becoming susceptible to tripping over wires or being electrically excited by the high voltage at the end of a wire. In the backcountry there is also the possibility of a representative of the ursus americanus community paying us a visit. For these reasons, among others, having a portable rig that can be set up, or moved, in a couple of minutes is a great advantage.

All these factors led me to build and deploy many of the antennas described in this blog. One in particular has led to a lot of discussion – the Coil-Loaded End-Fed Half-Wave (CLEFHW). This antenna comprises an 18.5ft telescopic stainless steel whip with a small loading coil at the base and a very short (0.05 wavelength) counterpoise.

What is “Electrical Length”

I made the claim that the loading coil changes the physical length from 18.5ft to an electrical length of a half wavelength on the 20m band. The choice of words is very important here. The physical length is measured in feet but the electrical length is measured in wavelengths.

Wikipedia defines electrical length thus:

In electrical engineering, electrical length is a dimensionless parameter equal to the physical length of an electrical conductor such as a cable or wire, divided by the wavelength of alternating current at a given frequency traveling through the conductor. In other words, it is the length of the conductor measured in wavelengths.

The purpose of the design was to eliminate long radial wires laying on the ground. A very short length of coax terminated in a common mode current choke acts as sufficient counterpoise. I wrote once before about a nice lady who stopped by to inquire, in a friendly manner, what I was doing. I was using a different antenna at the time and cautioned her to be careful of the wires on the ground. She responded by entertaining me with a little dance as she attempted to avoid stepping on them. Wires on ground in public spaces – ungood!

Another design objective of the CLEFHW was to be integral with a self-contained backpack kit occupying a ground footprint of only a couple of square feet. The backpack rig is its own operating table, so dump it on the ground, erect self-contained antenna, transmit. If I didn’t have worn out knees I wouldn’t even need a chair, but I did have to add an ingenious collapsible plastic stool to the kit.

Time for confessions

Now it’s mea culpa time … while the CLEFHW has performed successfully in more than one POTA activation and numerous casual QSOs, it does have a couple of design flaws. First, the biggest and baddest. A full-size vertical EFHW has a current maximum point half way up the antenna, far away from the power gobbling greedy green ground. But the CLEFHW cheats; it is not a physical half wavelength long, it is an electrical half wavelength long so the current maximum point remains at the base of the antenna. That results in high radiation around about head height. I checked with the ARRL RF exposure calculator and found that shouldn’t fry too many brain cells while operating at QRP levels. Proximity to ground also increases power loss. I mitigated this loss by raising the base of the antenna to about 1 meter above the terra firma. A few hundred milliwatts may still slip away to warm the worms, but heck, that’s the fun of QRP, so they say.

Another, shall we call it flaw, is the double impedance conversion. An email correspondent whose views I much respect advised me to think of loading coils as impedance matching devices. Using that way of thinking the CLEFHW’s loading coil converts the impedance of the whip to an R+jX value resembling that of a full-length EFHW. The 49:1 impedance transformer then reduces the impedance down close to 50+j0. There is almost certainly some inefficiency in that double transition. But, one of the design parameters already listed calls for Field Expedience above efficiency so I guess there is no free ride here. As somebody else once said: “every antenna is a compromise”.

The big, overriding objective of the CLEFHW design was to work as an integral element of a backpackable, rapid deployment portable ham radio kit. Despite some unusual quirks in its conception it gets the job done. Is it overly complex? Does the bizarre double impedance conversion cause more chaos than a monkey in a china shop? Should I abandon the design based on its assault on sound antenna physics? I seriously considered scrapping the project in favor of a Sweet and Simple tunable whip, but I am uncertain whether that would be an improvement.

The direction in which I am heading at the moment is to replace the 49:1 transformer with an L-match “tuner”, that is capable of dealing with the vagaries of terrain I experience in my itinerant portable operations. Despite widespread opinions describing End-Fed Half-Wave antennas in less than flattering language, the advantages for a portable operator outweigh any negatives so future endeavors will remain on that course.

As always, your feedback is much appreciated.

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 #CLEFHW #Counterpoise #CW #OutdoorOps #Portable #POTA

Is an EFHW Antenna Truly Multiband?

A fierce debate rages on one of the online forums I read. Is an End-Fed Half-Wave (EFHW) truly a multiband antenna? By “multiband” I mean resonant on even harmonics without a tuner. The most vocal posters in that forum keenly disparage these popular antennas despite their popularity.

Resonant on every band, earn DXCC in a single day!

It is possible to blow away a lot of money buying a commercial version of the EFHW for which vendors sometimes paint glamorous images of their product’s features and capabilities. That is one of the reasons the curmudgeonly forum folk like to open fire with their high caliber keyboard ammunition. They take shots at the popular broadband 49:1 impedance transformer, but reserve their most powerful ordnance for any claim of “multiband” performance.

Thousands of hams must be wrong

Strangely, many hams have used an EFHW with great success. It is a particularly popular antenna among SOTA and POTA activators. It only requires a single support structure; Canada has 300 billion environmentally friendly arboreal support structures available. An EFHW can be fed close to the ground because the feedpoint is a high voltage, low current point. A very short coax feedline can be used, or no feedline at all in fact. Some QRP operators don’t use any kind of counterpoise although a wire stub 0.05 wavelengths long is recommended – especially where no coax feedline is used.

Ham Radio Outside the Box decided to investigate whether an EFHW antenna is truly a tunerless multiband antenna. We were surprised by the results. For this study a 75/80 band EFHW was used. Can such an antenna operate on all the HF bands up to 30MHz?

Baby its cold outside

The current weather at my home QTH in the lee of mighty Lake Huron is typical for a harsh winter’s day in the High Arctic. But the High Arctic is 2000 miles further north so, even though those of us who make our homes here routinely stir our coffee with our thumbs (see note below), it’s a bit rough outside for erecting antennas. Being a coward when it comes to the cold I decided to perform this analysis by plugging numbers into a spreadsheet instead.

Note: A reference to the folk song “The Frozen Logger”

Let’s start in the band basement at 3500KHz:

Yes! It appears that an EFHW cut for the bottom of the band may be resonant on each of the even harmonics. As we move up the band to 3580KHz we lose the 6th harmonic on the 15m band.

Turning up the dial a little further to 3600KHz we now lose the 4th harmonic on the 20m band.

The 2nd harmonic on the 40m band disappears when we move up to 3700KHz

As we enter the phone portion of the band at 3750KHz we also lose the 8th harmonic. Now our antenna has become a monobander.

Let’s zip up to 3850KHz where (according to my ancient band plan chart) US General license holders get SSB access. Same result. In fact nothing changes all the way to the dizzying heights at the top of the band.

It seems that the best harmonic performance occurs at the bottom of the 75/80m band (in Canada we do not distinguish between 75m and 80m; everything from 3500 up to 4000 is referred to as 80m).

The HF bands have widely different bandwidths as seen below in this chart:

The band width chart suggests that we have very little expectation of finding a harmonic relationship between a wide band such as 75/80m and other bands – especially the WARC bands. Surprisingly, despite being the widest band, even 10m does not align too well.

Lets present the same chart from a different viewpoint using harmonic relationships.

In the chart above the bold vertical black line marks the origin frequency at each harmonic. Each HF band is then presented relative to the harmonic frequency. We can see that the 30m band is way out in left field while the 12m band is a near miss. In fact, if we cut our wire for a half-wave at 3560KHz something magic happens:

Now surprisingly we find a harmonic relationship on the 12m band, which is an odd (the 7th) harmonic.

Things to note:

• An EFHW antenna is only an exact half-wave on one frequency. However, adjacent frequencies may be close enough to still present an acceptable SWR to your radio.
• Conditions along an antenna repeat every half wavelength. It is therefore reasonable to expect resonance (or near resonance) at harmonic frequencies when those frequencies coincide with the higher bands.
• Harmonic relationships only make it more likely to obtain resonance on the higher bands; they do not guarantee it. Other factors also come into effect – for example, “broadband” 49:1 transformers.

What about those “lossy” 49:1 impedance transformers?

Ham Radio Outside the Box countered the myth about “lossy” inductors in our last post. Loss in an RF transformer has two sources.

• i^2*R heat loss. However, if the current “i” is very low – as it is indeed at the feedpoint of an EFHW antenna – these losses should be very small
• Magnetic coupling efficiency. This has so many variables that it is difficult to give a firm opinion.
  • Choosing the right ferrite mix for the frequency on which you plan to operate is probably significant. One ferrite mix may be optimized for the low bands while another is optimized for the high bands. If a toroid is chosen for, say, the low bands it may be less efficient on the higher bands. This alone makes multiband operation questionable.
  • How many ferrite cores should be used to avoid overheating? If a core gets above its “Curie temperature” its performance changes dramatically.
  • Is the transformer inside a sealed enclosure? If so it may overheat more quickly.
  • What size toroid is right for the RF power at which you will be operating?
  • What winding method is used for the transformer? Close wound or turns spread around the core? Autotransformer or separate primary and secondary?

What about a counterpoise?

Is a counterpoise necessary for an EFHW antenna? This is a “pistols at dawn” type of argument. The feedpoint of an EFHW has a very high impedance so the current is very small. Many QRP operators don’t use a counterpoise at all, but I have found it does have a small impact. If a coax is used then the outer surface of the braid is usually adequate for dissipating common mode current. Alternatively, a short counterpoise wire of one-twentieth of a wavelength at the lowest frequency of operation is recommended.

Does adding a short counterpoise turn an End-Fed Half-Wave antenna into a highly unbalanced Off-Center Fed Dipole (OCFD). Theoretically it does, but is that significant? Maybe not.

“1:1 SWR – perfect”!

It is often forgotten that the SWR at the rig end of a coax is usually not the same as the SWR at the antenna feedpoint. My RigExpert antenna analyzer allows me to null out any feedline by recalibrating at the rig end. And, finally, pressing the magic “Tune” button on your radio and getting a 1:1 match does not mean the antenna is just perfect. The function of a tuner is to provide a matching network between the input and output impedances, sometimes over quite a wide range. A 1:1 match at the radio might mean as much as a 10:1 SWR at the antenna!

Don’t worry, be happy!

Suppose we are more interested in making contacts then researching for a doctoral thesis on antenna physics. I actually did graduate with a bachelor’s degree in physics some 50 years ago and retain a passionate interest in the subject. But, when I am out in the Big Blue Sky Shack with a temporary antenna calling CQ and harvesting all the return calls for my log, I follow the following advice:

The antenna you have erected works better than the one you haven’t put up because you are unsure how efficient it might be.

While it is interesting and educational to learn and understand antenna theory it shouldn’t be a distraction from actually getting on the air. I like to think of the Special Operations Executive agents working behind enemy lines during the Second World War. Their typical antenna was a random wire passed through a window with the end thrown in a tree. They cared more about passing radio traffic and getting off the air quickly before the enemy arrived with their radio direction finding equipment … and machine guns.

Performing this theoretical analysis has helped me understand why there are widely different opinions about End-Fed Half-Wave antennas. I hope you too will find it useful.

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.

I did a little #casemod to my #beeLink #ryzen #miniPC to add external #antennas so I can pick up my neighbor's #xfinitywifi #hotspot better and I think I did a pretty good job! The clearance for the m.2 slot is pretty tight, but other than that I think it turned out pretty good.

Now to see if I improved the #wifi reception or made it worse 🤞