A Directional Antenna With Just One Straight Wire – Crazy?

Being called crazy is a compliment to my ears. It means I am doing something different, something unusual. I strive to be “crazy” every day. It is only by doing crazy stuff that we innovate and discover new ideas and new ways of doing things.

Today I decided to do two crazy things. First, I went outside to play radio in mid-winter. The temperature is only a couple of degrees below freezing but the wind made being out in the Big Blue Sky Shack a, shall we say, challenging experience.

Second, I wanted to experiment with one of my old favorite antennas – a long wire laid directly on the ground. A long wire is a wire that is at least one wavelength long. Laying a wire directly on the ground is next to impossible in Southern Ontario at the moment. We have a thick layer of fresh snow, so the ground is actually several inches further down.

In September 2021 I blogged about the K3MT Grasswire Antenna. If you don’t think a wire laid directly on the ground could possibly work, you should read that post; https://hamradiooutsidethebox.ca/2021/09/13/a-most-unusual-antenna/.

I should lay the blame for my latest bout of crazy behaviour at the door of well-known YouTuber Peter Parker VK3YE. I recently watched one of his videos in which he demonstrated the directional properties of a long wire – at his local beach. Peter lives in Melbourne, Australia where snow is something they only see in Christmas card pictures. Peter’s video prompted me to fire up EZNEC and model a 67ft wire laid on the ground for the 20m band.

The length of the wire is not critical. When a wire is laid on the ground it is detuned anyway. I chose this length because I had a scrap length available that just happened to be 67ft long. EZNEC gives virtually the same results for 62ft or even 84ft of wire.

Will It Tune?

Well, that’s a good question. It is essentially a long random wire and should be tunable in the same way as a random wire that is up in the air. I have a 9:1 unun that I could have used but instead I chose to use my home made L-match. An L-match tuner is ideal for matching the relatively high impedance of a long wire. Actually, it can also be used for matching very low impedance antennas too, but that’s another story. And, to answer the question, yes, getting a 1.5:1 match from my long wire laid in the snow was an easy job for the L-match.

What About a Counterpoise?

That’s another very good question. The purpose of a counterpoise is to provide “the other half” of an end-fed antenna. An alternative to a counterpoise is a good ground, like a set of radials, a long ground stake, or a water pipe. So, don’t we need a counterpoise – or a ground, or something with this antenna? A ground-mounted long-wire does what it does because the signal it carries interacts with its own reflection in the ground. If we were to attach a counterpoise, the antenna, if it could talk, would probably say “very nice, but what do I need that for?”

Yeah … But It’s Lossy eh?

Exactly! Hey, maybe we can work that loss to our advantage. Look at the propagation pattern in the EZNEC plot.

We have sacrificed gain for directionality. And, even though this is just a piece of wire laying on the ground (well alright … snow) most of our signal is headed in the direction of DX.

Now let’s deal with the antenna’s loss. EZNEC (set to high accuracy real ground for best prediction) shows a loss of 8.84dBi. Let’s call that 9dB so we don’t need to pull out a scientific calculator to figure out our effective radiated power.

A 9dB loss means only one eighth of our signal is making it out of the snow and up into the ionosphere. So our trade-off is to lose some signal in exchange for a highly directional antenna. How can we make that work to our advantage?

Let’s put this in the context of a POTA activation. Let’s say I am set up on a trail in Southern Ontario. The Bruce Trail (VE-5628) is a good example; it runs for 900km with many twists and turns. If I pick a section of the trail that is oriented north-south, I can lay my wire along the edge of the trail. It will be a stealthy antenna that probably won’t attract the ire of other trail users.

The Province of Ontario extends from the US border all the way up to James Bay in the near Arctic region. There aren’t many hams up that way, so all my contacts tend to be south of here. Perfect. My wire will radiate most of its signal to where it will reach the most hunters.

How much power is needed for a POTA activation?

Actually very little. K4SWL has demonstrated that as little 100mW can be enough. But let’s stick with the standard QRP CW level of 5 watts. If we want 5 watts out of our lossy antenna we have to crank the transceiver RF output up to a dizzying 40 watts. Out in the field, my Bioenno LiFePO4 12Ah battery can easily provide the necessary current for 40 watts so we’re good to go.

Now some readers will still question why we should throw away 87.5% of our power. Remember, it’s a trade-off. Nothing is free. In order to make a simple piece of wire into a directional antenna we have to pay a price. Not willing to pay the price? The alternative may be to carry a beam antenna into the field. That’s a good idea for ARRL Field Day maybe but not for a Parks On The Air activation.

What is the use case that makes a directional antenna so desirable?

Well, from my perspective, I want as much of the available signal as possible to be propagated towards where most of the POTA hunters are located. I do not need lots of power. When a POTA activator gets on the air the hunters will come-a-hunting. This antenna has a beamwidth of 45 degrees which will cover Florida to Texas and maybe beyond. It has a -30dB “gain” side-to-side so I can target the call areas I want to work. If I want to work the west coast I can simply change the direction in which the wire is pointing. And if the pile-ups become unmanageable I can reduce power to limit the distance my signal reaches.

So How Does It Perform?

An initial test of the antenna was very promising. Laid on top of several inches of snow, I was able to successfully tune the wire on the bottom end of 20m. Propagation conditions were not good. I received several stations clearly but attempts to dig out some RBN (Reverse Beacon Network) spots with an effective radiated power of only 2.5 watts were unsuccessful. The effect of the snow blanket is unpredictable so further tests will probably have to wait for better weather and dry ground.

In any event, it is an interesting experiment to take a crazy idea and test it in the real world. The whole idea of making a directional antenna out of one straight piece of wire flies in the face of all conventional wisdom – and that is what I like most about it.