#antennas — Public Fediverse posts

TechTip #3 Improving the “Titanic” 40m field expedient backpack portable antenna

TechTips on Ham Radio Outside the Box are brief posts of a technical nature.

Back in October 2024 Ham Radio Outside the Box introduced an interesting design for a compact, field portable antenna for the 40m band. Named the “Titanic”, it was a T-antenna similar in appearance to the one used on the tragically famous ship that sank in the Atlantic Ocean in 1912 during its maiden voyage. I recommend reading the original post to get the background information.

Recently I was wondering whether there is some way to improve the design by eliminating the loading coil without sacrificing the portability of the “Titanic”. It is a very simple design in which a shortened vertical element is top-loaded with two sloping wires acting as a capacitance hat. The vertical element can be supported on a short telescopic fiberglass pole.

There are two possibilities to consider: increase the length of the vertical element or, increase the length of the top hat wires. Or maybe both. After some experimenting I chose both options. Here are the design changes I implemented.

The revised “Titanic” antenna’s sloping top hat wires are supported on trekking poles, although raising the ends higher does improve the SWR. In order to preserve the rapid deployment feature of this field antenna the trekking pole support option, at about 4 feet, worked sufficiently well for me. The SWR seen by the radio at the far end of 25 feet of RG-58U coax is around 1.2:1.

Note the very compact size of this antenna. It is a stealthy option when operating in busy locations like public parks. It uses far less space than a 40m dipole and, if the dipole is erected as an inverted-V, it will exhibit the same omnidirectional radiation pattern, but perhaps with a lower take-off angle.

The “Titanic” should be considered an experimental antenna since I have not subjected it to field testing in a live-fire RF exercise yet, but it is a promising design that others have spoken well of (references available in the original post here on Ham Radio Outside the Box). If you try this antenna please let me know what kind of results you get.

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No loading coils, no top-hats, no transformers, no ununs, no baluns, no tuners, no radials – just the perfect antenna?

Just imagine, if you could get rid of all those lossy loading coils, impedance transformers, ununs, baluns, tuners and ground radial trip wires. What do you have left? Could it be the most perfect, the ultimate, 100% efficient, dream antenna? Yes, yes; it’s a dream! But back in the real world …

I spent most of the day recently, sweltering under a hot sun (suck it up John, the snow will be back before you know it) deploying all my recent experimental antennas, comparing results. It’s a lot of fun to experiment with various combinations of wire, whips, cores and coils, seeking “the one”, the best one, the antenna that will outperform expectations and fill the log book with DX galore.

Conditions that day were far less than perfect. Some stations I called faded away before the QSO was complete. Others couldn’t hear my 5000 mW signal at all. QSOs came along every few minutes of calling but most involved a struggle to squeeze enough microamps through my antenna to exchange signal reports and QTH. Every one of the antennas I tried bore the same result – until, out of desperation, I erected an antenna I had been keeping as an emergency backup. Suddenly the bands seemed alive; could this be “the one”?

We live on a Goldilocks planet

The Earth might be what astronomers call a “Goldilocks” planet – a planet with a breathable atmosphere, that is just the right distance from a star to maintain temperatures compatible with human life. Such planets are rare in the universe. Of course, there are areas on our planet that don’t meet the Goldilocks criteria and I’m sure Canada must be one of those areas. On a snowy, freezing cold day in February ain’t nothin’ gonna convince me I live on a Goldilocks planet.

But Goldilocks has a flaw – it doesn’t conduct electricity very well. I am sure you are wondering why this narrative has drifted off the topic of ham radio and into astronomy. Explanation coming. Maybe there would be all kinds of downsides to a planet that did have good electrical conductivity, but building antennas would not be one of them.

As a consequence we have to go to a lot of trouble to compensate for the Earth’s poor conductivity. One of my CW buddies has a full-size quarter-wave top-band vertical. It’s a monster of a vertical antenna and requires hundreds of ground radials to work. I am more of a field portable operator who likes to work with simple wire antennas. Something that can be deployed rapidly out in the field and taken down again just as quickly. I have used plenty of antennas that have ground radials and sometimes even had pleasing success with them. But, throwing just a few wires on the ground is inefficient, and when you are a QRP operator you don’t have watts to spare.

So, to sum up, sorry Goldilocks, but you can’t be part of my antenna; I need wire in the air, not on the ground. Before you reach for the comments section to remind me that the ground is always part of an antenna, yes you are correct. In fact even the ground thousands of kilometers away affects our antennas. Our signals, of course, bounce their way around the planet between the Earth and its ionosphere. And even a good antenna, on a day when the propagation gods are displeased, may be disappointing.

“The One”

How about a simple wire antenna that is one half wavelength long, fed in the center. You could call it a Center-Fed Half Wave (CFHW) but a simpler way to describe it is with the word “dipole”. I have never been a fan of dipoles in the past. First, they occupy a lot of space. A flat top dipole requires three supports which takes longer to erect. Feeding dipoles in the center implies a long length of coax which may lead to losses.

During a field deployment there are a couple of ways to mitigate these issues. If a dipole is erected as an Inverted V the horizontal space is reduced and only a single support is required. The radiation pattern changes from bi-directional to omni-directional, but maybe that’s sometimes a good thing. The ends of the dipole can be attached to the top of trekking poles, or simply pegged into the ground via a length of cord.

The long coax issue can be overcome using a sleeve dipole. A sleeve dipole comprises one quarter wavelength of coax and one quarter wavelength of wire. It is physically fed at one end, but the electrical feedpoint is in the center where the coax inner conductor is joined to the wire. The coax acts as part of the feedline while the outer surface of the coax braid forms a quarter wave element due to the skin effect.

There is a variant of the sleeve dipole called the Off-Center Fed Sleeve Dipole (OCFSD) which has been discussed here on Ham Radio Outside the Box in the past. The one I built supports multiple bands, but requires a 4:1 unun at the electrical feedpoint and a tuner in the shack. But, this post is all about keeping a simple wire antenna sweet and simple – no ununs, baluns, tuners etc allowed.

Another idea is to feed the dipole in the center using Open Wire Line (“OWL”). Now it becomes what is known as a “doublet”. OWL has very low loss, even over long runs. A doublet can support multiple bands with the aid of a tuner. But, again, this post is all about keeping a simple wire antenna sweet and simple – no ununs, baluns, tuners etc allowed.

Doesn’t a simple coax fed dipole require a balun at the feedpoint?

Technically, yes it does. If the dipole is perfectly symmetrical it is a balanced antenna. Feeding it with coax creates an interface between a balanced antenna and an unbalanced coax feedline. There is a possibility of common mode currents flowing back down the outer surface of the coax braid causing problems at the radio end.

Here we can get away with cheating a little. QRP operators have the advantage that any common mode current caused by lack of balance in the antenna, or by pickup of signal in the feedline will be very small and probably dissipate before reaching the radio. This little hack will probably not work at higher power.

But don’t you have to erect a dipole a half wavelength above ground?

No. Nein, nicht, non. For low angle radiation aimed at DX then, yes, erecting the feedpoint up high is definitely an advantage. But those of us activating or hunting any of the now numerous xOTA programs don’t have to follow that rule. I have had success with a 20m dipole with the apex at only 16ft. The angle of radiation is very high, but there is enough signal at lower angles to make intra-continental contacts. Similarly, my 40m dipole is targeted toward contacts in the eastern half of North America.

So simple dipoles it is then, or …

My antenna attention span can best be defined using quantum physics, i.e the science of things that are infinitesimally small. But for now I will be using simple wire dipoles for my field operations. Am I being too strict in my definition of “the one” antenna? Many a good contact has been made with miserably compromised whips, wands and wires. Perhaps my next venture will be a revisit with the Off-Center Fed Sleeve Dipole to explore how it compares with a pure, unadulterated dipole. Stay tuned.

Trust me I am a X-spurt

No really, but with the explanation that “X” is an unknown quantity and, according to the American Dictionary of the English Language, “spurt” is “a sudden forcible gush or jet” or, put another way: a short burst of energy. I have also heard “spurt” defined as “a drip under pressure”. So you can place whatever value you wish on my “X-spurtise”; it is based on endless tinkering and experimentation. I often venture down blind alleys and produce results that are worth the product of one-squared and infinity to the power of minus one. Occasionally I may also accidentally stumble on a good idea; I’ll let you be the judge.

Gallery

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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.

A short 2-band ladder line antenna for portable ops

Introducing the 2B2L antenna

Wouldn’t it be nice to have a short, fairly efficient, rapidly deployable, low visual impact, vertical antenna that can be operated on both the 20 meter and 40 meter bands? The 2B2L (2 Band Linear Loaded) antenna comes very close to a perfect match for those specifications.

The 2B2L is the brainchild of Tim KQ4TQ who pitched the idea to me in an email recently. Seeing the potential in Tim’s idea, I hastily built a prototype and erected it in my backyard for testing. The 2B2L is based on the “Simple Ladder Line Antenna for Portable Ops” discussed a couple of weeks ago here on Ham Radio Outside the Box. But here is the genius in the 2 band version: by adding a loading coil and a tail section – also made from ladder line – to the top of the original single band (20m) version, we can add the 40m band. The whole antenna towers up to the dizzying height of just 15 feet!

But, just a moment; before the grey-haired, white-coated men with a physics diploma hanging on the wall pick up their quill pens to denounce the 2B2L, a confession is in order. Yes, admittedly, the 2B2L is not perfect; field portable antennas rarely are perfect. Those of us who like to operate out in the Big Blue Sky Shack must necessarily accept some compromises. Those of us who like to operate QRP accept even more compromises. So where’s the gotcha?

The loading coil for the 40m extension is the weak link. It serves two purposes: (1) it acts as an RF choke for the lower 20m band section; it’s high impedance effectively terminates the lower section of the antenna so that the top section does not affect operation on 20 meters; (2) it acts as a loading coil for the 40 meter top section which is considerably shortened as a result. But is it actually all bad? Yes, it has some loss due to the i^2R effect, but consider this: the whole antenna is radiating on 40 meters and the coil is near the top where the current is lower. If I am thinking with half a brain here please correct me in the comments. I did once think I was wrong, but I was mistaken!

Can an antenna that is only 15 feet tall really be efficient on 20m and 40m? The secret to how it can claim enough efficiency to actually make contacts out in the field lies in its use of linear loaded elements. Two sections of ladder line, each shorted at the top, provide the linear loading which shortens the required length by about 30%. Linear loading is considered one of the most efficient ways of shortening an antenna.

Also, the 2B2L is mounted quite close to the ground which inevitably diverts some RF to warming the earthworms. Mine is fed about 12 inches (~30 cm) above ground. It could also be raised higher and used with tuned, raised radials, but on 40 meters the radials would each be around 33 feet long. I chose to use short ground radials instead.

Where to buy a 2B2L?

Sorry folks, this is another real hobbyist’s project – you gotta build it yourself. You’re going to need some ladder line from whatever source you go to for ham radio supplies. Mine was a generous gift from my friend and CW buddy Mary VE3MVM. You will also need a coil. I had an air core coil lying in the drawer from a previous project. I built it using a a short section of PVC tubing about 2 inches (5 cm) in diameter. You will need an inductance meter, or a NanoVNA, to measure the inductance. As a purely rough guide, my coil has 35 turns of 20 awg stranded insulated wire. Here is the materials list:

• 11.5 feet (3.5 meters) of ladder line for the 20 meter radiating element
• 38 inches (0.97 meters) of ladder line for the 40 meter extension
• 35 microhenry coil

Setting up the 2B2L antenna

The 2B2L can be erected on a pole about 16 feet (or about 5 meters) tall. It is fed at the bottom via coax to a transceiver. The 2B2L requires radials. I tried a set of 8 radials, each 7 feet (2 meters) long. That worked but 4 radials, each 13 feet long provided a better return path on 40 meters.

In keeping with recent practise here on Ham Radio Outside the Box, the radials are tuned with a GTU (Ground Tuning Unit). The GTU has to be separately adjusted for each of the two bands. This ensures that the antenna system is working as efficiently as possible – without a tuner! An antenna analyzer connected via a short coax showed an SWR well below 1.5 could be obtained on both bands.

Does it QSO?

No, it just sits there grinning at the sky, but I have QSO’d using the 2B2L. My best contact so far has been a 2000 kilometer QSO with a station in Colorado on 20 meters by QRP CW. 40 meters is most active in the early morning and in the evening when I am inactive, but I am going to have to make the effort to go 40 meter QSO hunting real soon. Stay tuned.

Help support HamRadioOutsidetheBox

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

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

TechTip#1 – a continuous loop of cordage

This is the first in an occasional series of short posts here on Ham Radio Outside the Box. The purpose of these TechTips is to share useful techniques I have learned over the years. I hope you will find them helpful.

TechTip#1 is an idea I picked up from a bushcraft video for creating a continuous loop of cordage. Of course, it is very easy to create a loop of cordage by simply tying the ends together with a knot. But that can be untidy and inconvenient, especially if the knot gets in the way of a neat join between two components of, for example, an antenna system.

How to use a continuous loop?

I use them a lot when erecting portable antennas. For example, if a cow hitch is formed at one end of the loop and a knot is tied at the end of a radial wire, the cow hitch can grip the wire end very securely – as long as tension is maintained in the loop. A second cow hitch can be formed at the other end of the loop to attach it to a tent stake. To release the wire simply pull out the tent stake, which relieves the tension and the wire is free.

Creating a continuous loop is surprisingly easy to do in just 3 simple steps.

STEP 1

Cut a length of thin cordage about 18 inches (46 cm) long. I use Atwood 1/16 inch (1.6 mm) Utility Rope, but any similar cordage, such as Bank Line, will do.

STEP 2

This is a very important step! Make sure both ends of the cordage are freshly cut, then melt the ends with a barbeque lighter, or similar. While the ends are still very hot press them gently together to form a bond. Be careful with this step because melted cordage can be quite painful if it gets on your hands. Being an amateur masochist I wait a couple of seconds then roll the join between two fingers to smooth the finished bond.

STEP 3

When the join has cooled – after just a few seconds – grab the loop either side of the join and pull like hell to test it. I was skeptical at first, but I can pull as hard as I like without breaking the bond. The Atwood cordage I use has a breaking strain of 110 lb (50 kg) and I suspect the join has the same strength.

If you have any similar amateur radio tips to share please send them to me via email, with photos if available and your tip will be featured here in a future Ham Radio Outside the Box TechTip.

Help support HamRadioOutsidetheBox

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

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RT @[email protected]

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