Mastodawn

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

Ham Radio Outside the Box Dec 15

A Year End Compendium of Outside the Box Antenna Ideas

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

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

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

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

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

ZZZZZ … ZZZZ … ZZZ

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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#amateurRadio2 #antennas #counterpoise #cw #outdoorOps #portable #pota

HamClock EOL

Ham Radio Outside the Box Nov 28

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

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

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

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

What is a Balun?

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

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

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

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

What is an Unun?

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

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

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

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

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

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

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

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

How to choose the correct device?

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

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

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

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

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

Gadzooks!

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

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

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

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

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

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

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

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

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#amateurRadio #antennas #counterpoise #cw #portable

Ham Radio Outside the Box Nov 21

POTA PERformer radials – can we make a compromise?

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

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

Now, to find a shortcut

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

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

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

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

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

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

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

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

Going back to my backyard tests, I found that:

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

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

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

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

Does this finding matter?

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

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

Changing the radiating element versus counterpoise lengths changes the impedance at the feedpoint.

The overall length of the dipole might change unexpectedly. This can be seen with Greg KJ6ER’s Challenger antenna which is a vertical OCFD halfwave dipole that is shortened by laying part of the counterpoise wire on the ground.

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

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

Not the best plan

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

The way forward

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

A final thought

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

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

Ham Radio Outside the Box Oct 14

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

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

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

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

There are two ways to perform an activation

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

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

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

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

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

Activating Arrowhead Provincial Park in the October sunshine surrounded by beautiful fall colors.

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

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

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

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

POTA activation at CA-0140 Arrowhead Provincial Park – October 2025

Smoke on the Wahta

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

Activating The Barrens

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

Exposed 2 Billion years old rock covers much of Torrance Barrens Serene natural beauty elsewhere at Torrance Barrens. Antenna worked fine – despite my failure to deploy the tripod’s top section!

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

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

POTA activation at CA-1669 Torrance Barrens Conservation Reserve – October 2025.
Good results despite improperly erected whip and a battery that ran out of charge!

A final word about the radials

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

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

Winter is fast approaching

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

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Ham Radio Outside the Box Jul 23, 2025

Does an antenna top hat really work?

Antenna “Top Hat” aka Capacitance Hat

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

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

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

To shorten the required physical length of a vertical antenna

To raise the maximum current point higher up the antenna

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

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

AliExpress top hat for a PAC-12 antenna. NB: I drilled a through hole in the hub to fit it on my tactical whip.

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

“Tactical” 9.5ft military style whip

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

How did it perform?

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

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

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

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

VA3KOT’s trail-hardened FT-891 rig with ham-made adjustable loading coil and 9.5ft top-hat loaded whip

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

Step One

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

Step Two

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

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

Bingo! (but no big prize)

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

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

Did the maximum current point clear the loading coil?

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

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

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#AmateurRadio #Antennas #Counterpoise #Ground #OutdoorOps #Portable