Which Antenna?

During the past years I have tried out several antennas. Some good, some bad. The better ones have found their way to this webpage. The worse ones are best left forgotten.

There is no easy way to determine which antenna is the “best”. It all depends on what you want it for. Before starting with beams I was certain that my goal was to get a beam. After using a couple of them I am not quite so sure any longer. Note that I have not used a tower and rotator in my experiments. The ability to change direction would be a good thing but before walking down that particular path, here are my experiences and thoughts on using fixed antennas, with possibly a fixed heading.

The problem with a beam in that it is “a beam”. It only looks in one major direction. And does its best to cancel what is coming from the opposite direction. If you are interested in one geographical area only then a beam would be fine, but that also includes selecting the “window” in time and frequency. As I can not be active during the light hours, except a couple of days in the summer holidays, my activities must be confined to the evenings and nights. And for DX and resonably sized beams this translates to 10 MHz, 14 MHz and perhaps even 18MHz sometimes.

And what will I find at these frequencies at night from my QTH in northern Europe? Not too many stations and certainly only a few in the preferred direction – where my beam is pointing. My circumstances turns a beam into a fairly troublesome gadget. It points in one direction only and, more or less, misses any other direction. Clearly not a best situation.

There is a mathematical relationship between the gain of a beam-antenna and the size of its lobe. A very high gain antenna will have a narrow lobe, there is no way to get past this fact. Conversely a wide lobe antenna will have a lower gain. You trade gain versus area covered. If you are looking for a high gain antenna then it will also require meticulous pointing to get the narrow lobe exactly where you want it. A few degrees off target and your fine antenna will have dropped several S-units. The narrow lobe thus comes at a cost! And, except under special circumstances, perhaps you are not willing to accept that cost?

There are however beams with wide and very wide lobes. In fact most vertically polarized directional antennas are wide in this sense and only the moxon two element beam is a horisontally polarized antenna with a particularily wide lobe. The wide lobe makes pinpointing less important, a wide field of view is beneficial when using only a fixed heading. The moxon and the vertical GSF-beam are very wide in this respect.

Using a beam to quench interference from behind is effective, and makes listening a pleasure, but is in no way a guarantee that the stations in the beam heading will hear you, even if you can hear them very well. If your output is low then your signal will not be distiguishable against the background, seen from the other stations position. So this is a battle lost.

Going from unidirectional antennas and understanding that they might not be the silver bullet you looked for there are many bi-directional antennas that can be rewarding to use. A bidirectional antenna with a wide lobe is close to an omnidirectional, so we can enjoy narrow lobe antennas here if we like, anything else is more or less pointless. A typical bidirectional vertically polarized antenna has a lobe width of about 60 degrees with a gain in the 4-5 dBi range (very generally speaking of course). The increased gain in the forward direction(s)s must be accompanied with a loss of gain elsewhere, so a 5 dBi gain bidirectional antenna has good rejection of signals perpendicular to the major beam(s). Less marked “waist” in the pattern gives less gain, and vice versa.

What about purely omnidirectional antennas then? For fixed work an omnidirectional antenna (any kind of vertical for example) can be very rewarding. You are guaranteed not to loose any direction so this type of antenna will be usable all around the clock and if you make a multiband vertical then I think it is the easiest way to become operative. Of course the omnidirectionality means that your antenna will pick up signals from all directions and that also includes interference. You will hear more, and part of what you hear you’d rather like not to have heard. The price to pay for a truly general antenna.

From my own experiments and simulations I have compiled a list of antennas. The gain and F/B-figures come from simulations, and are in my experience not too far off. I use this list myself as a guideline when deciding if I should try another antenna. There is no point in putting down the labour of building an antenna that does not promise to complete the already tested range. (The list is mine, it is not definitive and I can’t promise you will experience the same etc etc. You have been cautioned:)

Gain is given in dBi rounded to nearest integer, including ground reflections in the case of horisontal polarization, F/B is front-to-back ratio (dB), F/S is front-to-side ratio (dB), TOA (take-off angle) is in degrees at the height (in metres) indicated, size is length*width*height in metres for a frequency of 14 MHz. “Easy?” is my opinions of how easy it was to get up an running.

Type
Name
Gain (dBi)
F/B (dB)
F/S (dB)
TOA (degrees)
Size (metres)
Easy?
Omni
VHD
0
20 @ 1 m
0x0x10.2
Yes
Uni
Directional VHD
4
10
18 @ 1 m
3.37x0x10.6
Yes, you want this
Uni
Switchable VHD
4
10
17 @ 1 m
3.37x0x10.6
Fairly, but perhaps not worth it
Bidir
Halfsquare
4
15
21 @ 3 m
10.03x0x5.65
Easy, worthwhile
Bidir
Halfsquare beam
7
25
20
20 @ 3 m
10.03×2.40×6.06
Fairly, good lobe
Uni
GSF-beam
4
27
19 @ 3 m
8.00x0x5.00
Easy, good antenna
Bidir
Brucearray 4el
5
20
19 @ 3 m
16.05x0x5.35
Easy
Uni
Moxon
10
20
30 @ 0.5wl
2.93×7.68×0
Tricky, needs a tower

Some comments on the table above:

  • If you want an omnidirectional antenna for DX then the VHD is a good choice. If you also feed it with ladder line it will serve not only at 14 MHz but at all frequencies from 10 MHz to 28 MHz. This includes the hassle of using a tuner. I believe it is worth the hassle.
  • A small amount of directionality (which might be just what is needed to nail that elusive DX) can easily be achieved with a hanging wire reflector as in the Directional VHD. This is an easy addition, is “cost effective” and is recommended. The directionality is only for the design frequency, it is still usable and omnidirectional at other frequencies.
  • In the bidirectional realm, the halfsquare, HSQ, is an excellent antenna. Decent gain and area coverage. You should at least try this one once in your life:) It is however a fairly narrow (frequency wise) monobander.
  • The HSQBeam is my best to date. It is a monobander and has excellent punch and F/B-ratio. The lobe is wide enough to make in useful in more than point to point communication.
  • The GSF-beam is a portable beauty. Easy to erect and good gain with very decent F/B-ratio. Single bander if fed with coax and fair omnidirectional multibander from 10 MHz and up if fed with ladder. And you’ve aleady got that tuner, right? Tilt this, make it lie flat and you have higher gain due to the now horisontal polarisation. Tilt it just a little and you will enjoy a bit of both polarisations. This is not a picky antenna.
  • I use the Brucearray for 10-28 MHz fed with 300 ohm ladder line. Shorting the ladder line and using the whole kaboodle as an end fed wire with capacitive load against a few metres of counterpoise works for 3.5 and 7 MHz. I have no more figures on this usage however.
  • The crown in my menagery is the moxon. Good gain, excellent F/B and with the bidirectional device and trimming as described elsewhere on this site. Must get up in the air though and I had troubles with it on my roof as I couldn’t reach all parts of it. Collects snow and weighs a lot then!
  • So what is most bang for the buck? In this order and in my opinion: VHD, Halfsquare, GSF-beam or Brucearray. After this they tend to get more complicated and need care and feeding to work and work and … I really would have wanted the HSQB in the list, a very good antenna for a specific purpose but it is not general enough, sorry. I want an easy life. YMMV.

Using large, efficient and hi-gain, hi-F/B-antennas combined with outputs in the kilowatt range will let you have high DX-QSO-rate. But where’s the fun in that? The GSM-telephone is also an ample choice in that case…

Determine your personal “profile” and stick to that. Make the most out of the hobby with the tools you have. Most of us have only meager tools and/or circumstances and will have to settle for simpler setups. Fiddling with antennas is one way of bringing back experimenting into the hobby and have great fun at the same time!

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