Mastodawn

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).

The KQ4TQ GTU deployed with a linear-loaded radiating element and a tuned linear-loaded counterpoise

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:

Repackaged KQ4TQ GTU with modifications

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.

Repackaged KQ4TQ GTU interior

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.

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#AmateurRadio #Antennas #Counterpoise #Ground #OutdoorOps

Ham Radio Outside the Box May 7

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 current sensor and RigExpert antenna analyzer pictured in another experiment

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.

Linear-loaded monopole with Magic Carpet held down with rocks to withstand the wind coming across 100 miles of Lake Huron!

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

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#AmateurRadio #Antennas #Counterpoise #Ground #OutdoorOps

Bryan King Apr 29

The Cloud-Burner: How to Master NVIS for Reliable Local Comms

1,593 words, 8 minutes read time.

If you have just earned your Technician or General class license, you have probably already realized that the radio world is full of “dead zones.” You might be able to talk to a guy in Italy using a massive tower, or a guy across town using a local repeater, but what about the people two counties over? Often, that sixty to two-hundred-mile range is a “skip zone” where your signal just flies right over their heads. This is where Near-Vertical Incidence Skywave, or NVIS, comes in. Think of it as taking your radio signal and pointing it straight up at the sky, using the atmosphere like a giant mirror to bounce that energy right back down into your local region. It is the ultimate tool for keeping your community connected when the internet goes out or the repeaters fail. It doesn’t require a hundred-foot tower or a thousand-dollar antenna; it requires a little bit of wire, a low branch, and the willingness to learn how the air above your head actually works.

Understanding the Ionospheric Mirror

To get a handle on NVIS, you have to understand that the ionosphere isn’t just empty space; it’s a layer of the atmosphere filled with particles that have been “charged up” by the sun. We call this ionization. During the day, the sun is hitting these layers hard, making them thick and reflective. At night, they thin out. For NVIS to work, we need to pick a frequency that is low enough to be reflected back down rather than passing through into space. This is governed by something called the Critical Frequency, or $f_c$. If you try to send a signal straight up at a frequency higher than $f_c$, it’s gone forever. For new hams, the rule of thumb is simple: use the 40-meter band (7 MHz) during the bright part of the day, and move down to the 80-meter band (3.5 MHz) or 160-meter band (1.8 MHz) as the sun goes down.

The goal here is to keep your “angle of incidence” near ninety degrees. Imagine standing in a room with a flashlight and a mirror on the ceiling. If you shine the light at a sharp angle toward the wall, the light bounces off and hits the far corner of the room—that is your standard long-distance “DX” skip. But if you shine that flashlight straight up at the ceiling, the light bounces right back down onto your head. That is NVIS. By “burning the clouds” with your signal, you create a solid umbrella of coverage that fills in all those local gaps. The math behind this is surprisingly straightforward. The Maximum Usable Frequency (MUF) for your local area is roughly equal to that Critical Frequency because the “Secant” of your ninety-degree angle is essentially one:

$$MUF = f_c \cdot \sec(0^\circ) = f_c \cdot 1$$

When you stay below that $f_c$ limit, you ensure your signal doesn’t punch through the atmosphere and disappear. Instead, you get a reliable, high-strength signal that blankets your entire region, regardless of hills, buildings, or trees that might block a standard line-of-sight signal.

The Low-Hanging Wire: Your NVIS Antenna

The most common mistake new hams make with NVIS is trying to get their antenna too high. We are taught that height is king, but in the NVIS world, the ground is actually your friend. To push your signal straight up, you want a horizontal dipole antenna mounted very low—usually only 10 to 15 feet off the ground. When the antenna is this low, the radio waves that hit the ground reflect back up and join with the waves going toward the sky. This creates a massive “lobe” of energy pointing at the zenith. If you put that same antenna 50 feet in the air, the energy starts to focus toward the horizon, which is great for talking to Japan, but terrible for talking to the next town over.

When you build a low antenna, the “impedance” of the wire changes. Impedance, represented by the letter $Z$, is basically how much the antenna resists the flow of electricity from your radio. A standard dipole in free space is about 72 ohms, but when you bring it close to the dirt, that number drops. You might see your SWR (Standing Wave Ratio) jump around because the ground is “soaking up” some of that energy or reflecting it back into the wire. The formula for this total resistance looks like this:

$$Z = R_{rad} + R_{loss}$$

Your goal is to keep $R_{rad}$ (the energy actually leaving the antenna) high and $R_{loss}$ (the energy turning into heat in the dirt) low. You can help this by laying a “reflector wire” on the ground directly underneath your antenna. This acts like a mirror on the floor, bouncing even more energy up toward the sky and away from the dirt. It is a simple, cheap way to make a basic wire antenna perform like a professional military setup. It is about working smarter with the space you have, using the foundation of the earth to amplify your reach.

Operating with Discipline and Purpose

NVIS isn’t just about the gear; it’s about the man behind the mic. Because you are using lower frequencies like 40 and 80 meters, you are going to encounter a lot of noise. These bands are where lightning crashes and electronic interference from house appliances live. To be successful, you have to develop a “radio ear.” You learn to listen through the static for your brothers. You also have to be ready to change bands. If you’re talking on 40 meters and the signals start to fade as the sun sets, don’t just keep cranking the power. That is a waste of electricity and hard on your gear. Instead, understand that the ionosphere is changing. Be the leader who says, “The sun is going down, the critical frequency is dropping—let’s move the net to 80 meters.”

This kind of communication is a responsibility. In an emergency, NVIS is often the only thing that works when the cell towers are down and the repeaters have no power. As a new ham, mastering this technique means you are becoming a valuable asset to your family and your community. You aren’t just playing with a hobby; you are learning the physics of the atmosphere so you can provide a lifeline when it matters most. It takes patience to learn the cycles of the sun and the quirks of your local soil, but that discipline is what separates a true operator from someone who just bought a radio.

Take pride in the “bench time.” Build your own dipoles, experiment with different heights, and don’t be afraid to fail. Every time you tune an antenna or successfully make a contact two towns over during a storm, you are gaining technical mastery. You are learning to provide for those around you by using your mind and your hands. Keep your station clean, keep your character grounded, and remember that the strength of the airwaves comes from the discipline of the men who use them. Whether you are a Technician just starting out or a General looking to expand your skills, NVIS is the gateway to a whole new level of radio capability.

Looking Ahead: The Power of Local Links

The future of radio isn’t just in satellites or high-speed digital networks; it’s in the resilient, local links that we build ourselves. As you grow in this craft, you’ll find that NVIS is a bridge. It connects people across distances that are too far to see but too close for standard skip. It is a testament to the order of the world—that even the very air above us is designed in a way that allows us to reach out to one another. By mastering the “Cloud-Burner” technique, you are stepping into a long tradition of operators who value self-reliance and technical skill.

Continue to study the $SFI$ (Solar Flux Index) and watch how the bands open and close. Treat your fellow hams with respect and kindness, and always be willing to help the next new guy who is trying to figure out why his signal isn’t getting out. We are a community built on shared knowledge and a commitment to the craft. Stand tall, keep your wires taught, and we will see you on the air.

Call to Action

If this story caught your attention, don’t just scroll past. Join the community—men sharing skills, stories, and experiences. Subscribe for more posts like this, drop a comment about your projects or lessons learned, or reach out and tell me what you’re building or experimenting with. Let’s grow together.

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D. Bryan King

Sources

Disclaimer:

The views and opinions expressed in this post are solely those of the author. The information provided is based on personal research, experience, and understanding of the subject matter at the time of writing. Readers should consult relevant experts or authorities for specific guidance related to their unique situations.

#ZRJX #160MeterBand #40MeterBand #80MeterBand #amateurExtra #AmateurRadio #antennaEngineering #antennaHeight #antennaTuning #AS2259 #BenchCraft #Counterpoise #CriticalFrequency #CW #DLayerAbsorption #digitalModes #ElectromagneticRadiation #EMCOMM #emergencyCommunications #F2Layer #GeneralClass #GroundLoss #groundPlane #hamRadio #HorizontalDipole #impedanceMatching #ionosphere #MUF #NearVerticalIncidenceSkywave #NVIS #PlasmaFrequency #RadiationResistance #radioDiscipline #RadioNet #radioPropagation #Refraction #RegionalRadio #RFPhysics #SecantLaw #selfReliance #signalFading #signalToNoiseRatio #SkipZone #SolarFluxIndex #SSB #SWR #TacticalComms #TechnicalSovereignty #technicianClass #wireAntenna #ZenithRadiation

Ham Radio Outside the Box Apr 15

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”.

Home made ladder line. The separators are made of shrink wrap heated with a Weller soldering gun with plastic welding tip. Lots of work and not very elegant, but practical and cheap!

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.

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Ham Radio Outside the Box Apr 8

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.

Hiking antenna 01: a Linear-Loaded Monopole Hiking antenna 02: 13ft tripod/whip

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.

20m 2T2C ground coupler

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?

MacGyver inspired binocular core

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!

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Ham Radio Outside the Box Mar 25

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.

Current in a ground-mounted quarter-wave antenna. Green line represents ground.

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.

End-Fed Half-Wave antenna current distribution

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.

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Ham Radio Outside the Box Mar 18

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.

Superbly engineered variable inductor inside the Miracle 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?

Short antenna seen outside

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.

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Ham Radio Outside the Box Mar 11

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 SWR is hard to read due to the bright sunlight – it is 13. The GTU had not yet been adjusted for maximum counterpoise current. Observe the small deflection on the RF current meter. The SWR is difficult to read due to the bright sunlight; it reads 1.79.
The strange blue thing in the antenna wire is a small loading coil.
Observe the higher deflection on the RF current meter after the GTU had been adjusted for maximum current in the counterpoise.

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.

GTU atop its chicken wire capacitance plate. The large toggle switch bottom right is a bypass switch. The knob under the meter selects one of three inductors. The knob at top right adjusts the deflection of the meter needle. The large knob is for the tuning capacitor.

The final setup – will it QSO?

Final setup. This picture was taken before the chicken wire capacitance plate was in place. The antenna was fed by a 10ft RG-8 coax through a Common Mode Current choke (on a FT240-31 toroid)

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?

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Ham Radio Outside the Box Feb 4

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.

You heard the expression “looks like a million dollars”? Well this looks like a single solitary buck – but it works!

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!

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Ham Radio Outside the Box Jan 8

Great ideas from Ham Radio Outside the Box subscribers

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.

Copper mesh – source: Amazon.com

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.

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#AmateurRadio #Antennas #Counterpoise