Antenna Height Matters – True or False?

How often have you read that an antenna should be placed as high as possible – the higher the better? Is it true? My inner skeptic says “hmm, maybe”. It’s certainly an aphorism that is open to scrutiny. Aphorism? The American Heritage® Dictionary of the English Language defines “aphorism” as: “a tersely phrased statement of a truth or opinion”.

I’ve got wires in low places

The problem with tersely phrased statements of a truth or opinion is they get repeated so often that people begin to accept them as unchallengeable fact. “The higher the better” may actually be perfectly good advice – in some circumstances. A good friend and code buddy of mine is a farmer. He farms antennas. Among the many wires and towers on his property are three 1200 feet long beverage antennas that are just high enough to allow his tractor to pass beneath them. He is a devotee of the “Gentleman’s Band” (160m) and uses his beverage antennas for receive only. His transmitting antenna is a full size quarter wave vertical – a 130ft tall tower with enough radials to trigger a global shortage of wire.

“Beverage antennas are for receiving only, you can’t use them for transmitting”. There must be a stone tablet somewhere with those exact words engraved on it. Well, why not transmit into a Beverage antenna? I wrote a post some time ago with the title “A 200ft Antenna Up Zero Feet – How Does it Perform” about a “grasswire” antenna I had built. It comprised 200 feet of wire laid directly on the ground. “Oh, no! All your signal will be absorbed by the ground” the voice in my head was telling me. Except it wasn’t. I QSOd on that antenna more than once. The theory of why it works is laid down in another old post: A Most Unusual Antenna.

Another strange but proven antenna

European blogger and podcaster Ed Durrant introduced me to what I initially perceived to be a very bizarre antenna – the VP2E (Vertically Polarized 2-Element). It is a monoband wire antenna with one very interesting feature – the apex of the 20m version that I built is only about 14 feet high. And yes it works fine business; I have completed several POTA activations with it. The low profile makes this a stealthy antenna that is less likely to attract the curiosity and suspicions of other non-ham users of public spaces.

So what about the popular End-Fed Half Wave (EFHW) antenna?

One of the many online forums I read regularly is populated by a group of commenters that, shall we say, do not fully endorse the benefits of the EFHW antenna. It may be true that the EFHW is often used in a manner that does not bring out its best features. A popular version of the EFHW comprises an electrical half-wavelength of wire fed through a broadband 49:1 transformer. The problem is it gets treated as a resonant multi-band antenna. It has SWR dips on its fundamental frequency and harmonics, but the bands are not exactly harmonically related. No problem, some hams believe, just press the tune button on the radio and hey presto 1:1! Yes, the radio sees 1:1, but that doesn’t make the antenna, at the other end of the coax, resonant.

Before we get back to the main topic of this post let me just outline a version of the EFHW that overcomes the issue just discussed – the linked End-Fed Half Wave antenna.

Opening or closing the links optimizes operation on my 3 bands of interest – 20m, 30m and 40m.

The antenna is resonant on each band and does not have to rely on harmonics, although it works well on all three bands with all links connected. And no tuner is required!

How low can you go?

Field portable operators like myself find it essential that all antennas can be rapidly deployed and are as lightweight as possible. If I have to haul my aging bones, weighed down by all my gear, up the steep rocky inclines of the Niagara Escarpment, weight counts. It is truly surprising how much extra gear accompanies my tiny QRP transceiver on a field trip.

If an EFHW is deployed in typical fashion it requires a suitable tree for support. Or, in the absence of a suitable tree, a pole. “The higher the better” right? I have a fiberglass pole that will get a wire up 30 feet, but it is quite heavy. So I asked myself if it is really necessary to go up that high. Perhaps a shorter, lighter pole could be used, but how will that affect antenna performance?

Reach for the sky

Picture this; a 40m EFHW antenna is erected supported by a 33ft pole at its center. If the angle between the two wire sections is 120 degrees (greater than 90 degrees is recommended), the ends of the wire will need additional supports. What, now three poles to haul up the trail?

We often hear of SOTA operators using EFHW antennas and mounting them on short poles. There is one brand of telescoping pole that extends to 20 feet, yet can be collapsed small enough to fit in a backpack. Maybe I’ll buy one some day, but for now I have rigged a fairly sturdy telescoping 16ft pole that is ultra light, although it is still 4ft long when collapsed.

So what do computer models have to say about working with an EFHW for 20m, 30m and 40m that is only 16ft tall at its apex? I should add that this idea is helped by the feedpoint of an EFHW being a high voltage/low current point and can therefore be mounted very close to ground.

NB: The following radiation pattern charts are based on using the full length of the antenna with all links connected. My own build of the antenna gives an SWR well below 2:1 on all three bands without a tuner in this configuration.

The radiation pattern on 20m is the familiar donut shape with maximum RF energy at 25 degrees to the horizon at a broadside azimuth of 85 degrees.

There is even about a half S-unit of gain. For good DX the radiated signal is still at unity gain down to 10 degrees.

On 30m the picture is a little different with most of the radiated energy at 65 degrees elevation. However, the antenna still performs well down to an elevation of 20 degrees, but at an azimuth of 50 degrees.

Disadvantage? No, in fact the directionality of the antenna could be an asset by allowing the antenna to be oriented to favor a desired direction.

On 40m, as expected, the antenna acts as an NVIS (Near Vertical Incidence Skywave) antenna for local contacts within a few hundred kilometers from the transmitting station.

But, look closely and you can see a lot of signal going out down to an elevation of 40 degrees which should cover whichever continent you are on. Good predicted gain too.

No tree, no pole, no problem

Leave the pole at home but take a buddy along for the outdoor operating session. Ask him to hold the center of your wire above his head. You can reassure him that the high voltage points on 40m are well away from him, just don’t switch to 20m. Ok, don’t really do that please. My point is that the antenna will still work (according to the models) with the apex down at six feet above ground.

At that very low apex height the radiation pattern on 20m changes from broadside to firing RF off the far end of the wire at a still useful +/- 3dB elevation between 20 and 50 degrees. Strangely, that is similar to the radiation pattern of the VP2E we discussed earlier. Maybe I’m getting closer to understanding how that strange beast works.

Efficiency?

We haven’t entirely forgotten about antenna efficiency and yes, proximity to the ground does result in some of our signal being swallowed by our friendly home planet. But there are conflicting objectives based on whether we are designing an antenna that adheres to the laws of physics (I am a college physics grad) or, we need a field expedient, rapidly deployable temporary antenna that will grab a few quick QSOs before being torn down and packed away.

Think of it this way, if we really placed the greatest importance on efficiency and getting the best signal reports, we would throw away our QRP radios and carry a legal maximum linear amplifier into the field. Why deliberately use only 5 watts when you could be pumping out enough power to stay warm in winter?

Since operating QRP is one of the most popular activities in the world of ham radio it would seem we have already made that decision. A field antenna doesn’t have to be perfect, it just has to be efficient enough to fill the log sheet.

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