ANTENNA PREFERENCES–VERTICAL VS HORIZONTAL
Every now and then the debate over vertical vs horizontal antennas comes bubbling to the surface in the amateur radio press. The articles produce the usual exchange of views, with most of us caught between two premises: vertical antennas radiate equally well (or poorly) in all directions and horizontal antennas offer “ground reflection gain” of typically 6 dB, giving them an edge over vertical antennas. The truth lies somewhere in between, depending on your ground conductivity, local antenna restrictions, and materials available.
In the December 2012 issue of “QST”, Joel R. Hallas, W1ZR, examines the case for each antenna system and offers some guidance for those of us who may be forced to choose one antenna over the other. “Vertical or Horizontal HF Antennas–What’s Best for You? If you can have only one HF antenna, how do you choose?” (page 45).
The article is clear, concise, and on target when it comes to explaining the advantages and disadvantages of each antenna type. Hallas supplies some simple elevation patterns to illustrate his points.
Briefly, Hallas says “a ground mounted or elevated vertical monopole with a length of 1/4 wavelength or less will tend to radiate at low angles, but how much and how low depends on the ground conditions surrounding the antenna at some distance.” Hence, the need for an effective ground radial or tuned counterpoise system if your antenna site is far removed from salt water or marshy ground. One can see this effect is action when DX-peditions position there vertical arrays near salt water. In past articles, Hallas has encouraged amateur radio operators to think of ground losses with verticals because “most of us don’t have the advantage of an ocean at our doorstep and we have the pattern resulting from the signal traveling along the surface of a lossy earth.”
I found this idea quite true when I worked at a commercial AM radio station in Hilo, Hawaii. Before the KHLO-AM (850 Khz) tower was lost in 1996, the station had an old base-loaded self-supporting tower (only 180-feet tall) sitting in a salt water marsh about 60 yards from Hilo Bay. The radial field extended into the marsh, which gave the station an exceptionally good ground. Our puny 1 kw power got the station into Europe, Asia, and even as far as the mid-west of the mainland United States. When the station leased a tower about 4 miles from ocean, it took 5 kw to cover the same day time service area that the old 1 kw transmitter was delivering.
As for horizontal antennas, Hallas notes that “the ground reflection gain reinforces radiation at particular ranges of elevation angles depending on the height of the antenna above ground.” At elevations below 1/2 wavelength, the horizontal antenna fires a lot of rf at high angles–perfect for NVIS (near vertical incident skywave) propagation. Before I built my 40 meter under-the-house loop, I used a 40 meter dipole at 15 feet off the ground to join various interisland nets. The signal was strong out to about 200-300 miles, just right for covering the length of the state of Hawaii.
Hallas also notes that, unlike a properly built vertical, a horizontally polarized antenna is directional–“favoring the directions perpendicular to the conductor. This is more significant as the dipole gets higher. At a height of 3/4 wave, the dipole is down 16 dB at the ends, arguing for another antenna, if you want coverage in all directions.”
So, what does one do, when circumstances dictate the use of only one antenna? Hallas says use the antenna that best fits your situation and enjoy it–“even if you wish for something different.” If you want to pursue DX and are confined to ordinary ground conditions, “you can expect better results with a vertical until you can get a horizontal antenna higher than at least 1/2 wavelength.” Hallas adds that this is not a difficult problem if you are chasing contacts on bands higher than 40 meters. For example, a “height of 1/2 wavelength is about 17 feet on 10 meters, while it is about 130 feet high on 80 meters.”
Of course, your mileage may vary, depending on your location and various restrictions. In my present location, I use a homebrew 20 meter vertical dipole for DX work and a 40 meter-under-the-house loop for local contacts. Each antenna works well for its intended purpose. I also get 20 to 10 meter coverage from my 20 meter delta loop in the back yard. I feed this loop with 450-ohm ladder line. I can get either vertical or horizontal polarization depending on whether I attach the feed line to the top of the mast or at a corner of the delta loop.
If you can manage both a vertical and a horizontal antenna, you can have the best of both worlds. I say this knowing full well that, in the back of my unsettled mind, I really want a 100-foot tower with a 4-element 20 meter beam on top. But, reality rears its ugly head and I must work with what I have. Check out Hallas’s article. It may help you decide the kind of antenna you really need. Have fun.
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Aloha es 73 de Russ, KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.
Filed under: Amateur Radio