DX RX

The Doctor of DX prescribes the
answers to your problems, low and
high, near and far.

A how to of what for, by Mike(aka Billy)Graham, K7CTW

TOPBAND

Today, as I am writing this column (8 March, 1998) I am celebrating my 40th anniversary as an amateur radio operator. From my very first QSO, which was with a VE7, to today, there has always been a big thrill when working hams in foreign countries. But having worked (at one time or another) every radio country out there and having been DX in such places as Hawaii, Okinawa, Japan, Midway, Australia, Manila Bay, Cuba, Barbados, Puerto Rico, Guantanamo Bay, and especially Bahrain Island, boredom was setting in. In the past 2 years that has begun to change, thanks to 2 books and one of our own club members.

John Devoldere, ON4UN, devotes a great deal of his book "Low-Band DXing" to transmitting and receiving antennas used on 160 Meters (Topband). The book is a classic resource of information for those interested in improving their transmitting and receiving antennas for the 160/80/40 Meter bands. A second book, "Dxing on the Edge: The Thrill of 160 Meters" by Jeff Briggs, K1ZM, is not only a superb reference guide to 160 Meters, but is also a fascinating tribute to "Mr. 160", Stew Perry, W1BB, and to the tenacity of the many other pioneering hams who have devoted their amateur interests to Topband.

In the spring of 1996 Ed, K2TE, our own "Mr. Contester", asked for some assistance to get his new 160-Meter Inverted "L" transmitting antenna and a receiving Beverage antenna strung. During the several hours that we worked, Ed related to me the challenges that 160 meters posed as well as the "big kick" he received when finally snagging a new one. Intrigued by his enthusiasm, I "jury-rigged" a 100-foot dipole fed with 450-ohm ladder line and ran that to the balanced output of my tuner. During the next several weeks there were a couple of contests and the big DX guns were there en masse. I was surprised to hear these guys working DX stations that I couldn't even hear! Then during the WPX contest later, these same fellows were pleading over the spotting networks for everyone to get on 160 and "load up your bedsprings" to give them a QSO point. So I tried it. Much to my surprise, they could hear me. That open- wire fed dipole was the saddest thing you ever saw. But it was an incentive. So last Fall I stuck up my "Forest Fire Dipole", again thanks to Ed ("Have Wrist Rocket - Will Travel"). We got it up there a good 60- 65 feet. I was not overly optimistic that it would perform well, especially on receive. But the results thus far have been amazing: 27 Countries and 35 States worked. Just think of what I could have done with a good Inverted "L" and a couple of Beverages.

Incidentally, the "Forest Fire Dipole" is so named due to the fact that, as a result of icing on one of the plastic end insulators, it caught fire a couple weeks ago from arc- over. Some poor passerby saw this fire up in my big pines and came frantically knocking on my door. We ran back outside just in time to watch the one end of the antenna "twang" loose. Hey, now that's what I call a "HOT" antenna!! John, WS1E, gave me some "real" ceramic insulators about a foot long and thus far I've not been able to start another fire, although I've tried.

Transmitting Antennas

On Topband, rotatable arrays are obviously pretty much out of the question. Dipoles and loaded dipoles, such as mine, do work, but height above ground is important. Low height dipoles or low Inverted-V antennas exhibit very high angles of radiation, and are thus not effective for DX. Commercially available short verticals do not perform very well either, regardless of claims. For serious Topband performance there are some far more effective and perhaps cheaper ways to be a "heavy hitter".

The first method involves using an existing non-insulated ground-mounted tower as a folded unipole. A 60-70 foot tower with a tribander atop does work quite nicely. It will require a number of radials, at least 32 of them 1/4-wavelength (130 feet) long. The tower is shunt-fed with a birdcage 3- wire gamma array which is held off from the tower a distance of 12-15 inches. The base of the birdcage array is connected to a Gamma or Omega match at the base of the tower. Details of such an array can be found in both books cited previously.

Another approach, and perhaps cheapest and best, is the Inverted-L antenna. The vertical component should be 40-70 feet in length, with the horizontal component being the remainder. Total length should be 133 feet to resonate at 1830 kHz, the DX "Window" frequency. 50-ohm coax feeds it, with the center conductor connected to the antenna, and the shield connected to a radial network underneath. The radial network is important, as above, and the more radials the merrier. If you use an elevated Inverted-L, 3 radials spaced 120 degrees will work. Once again, the books previously cited contain a great deal of literature on building these superb transmitting antennas.

Finally, if you are getting super-serious about 160, there are a number of designs utilizing the Inverted-L in two and 4- element phased arrays which give superior performance. The use of these arrays does require, however, that you have the real estate available to erect them.

Receiving Antennas

Sadly, the first and biggest lesson learned when beginning your foray into the realm of Topband is the fact that efficient radiators do not make very good "ears". Since most transmitting antennas for 160 are verticals of some form or other, they are rather poor receiving antennas. This is compounded by the traditionally high noise levels experienced on 160 and typically weak incoming signals from DX or stateside stations at a great distance. Much work has been done in this respect and several antenna designs are superb for 160 meter receiving.

The most venerable, simple and perhaps best receiving antenna is the Beverage, named for its inventor, Harold Beverage. It is nothing more than a very long wire (1 or 2 wavelengths) aimed in the direction of interest. Low-angle radio waves traveling along the wire from the direction of interest propagate as waves and build in amplitude as they reach the feedpoint. This is why the Beverage antenna is sometimes referred to as a "Traveling Wave" antenna. Because local high angle signals and atmospherics do not propagate well along the antenna, they are very "quiet" and produce a far superior signal-to-noise ratio over other antenna types, even though total signal level may be considerably less. Mounted about 10-12 feet above ground, they can be made from insulated stranded #12 or #14 wire, and hung in trees along their length. The insulation has an added benefit of reducing rain or snow static which will increase on bare wire. Bare wire also grounds against tree limbs and trunks. Coax is used with a suitable balun (usually 9:1) at the feedpoint.

For omni-directional characteristics, the end of the antenna is terminated in a non- inductive resistor of between 300-450 ohms. For bi-directional characteristics, the end is left unterminated. Beverages usually work quite well if they can be made at least 400 feet in length, but is preferable that their length be either 540 feet (1 wavelength) or 1080 feet (2 wavelengths). Obviously, this is not a solution for everyone, as neighbors may object. But even a wire 300-400 feet long will improve reception. This was confirmed by several 160 meter friends of mine who have used the shortened versions.

For you land-poor folks, Jeff Briggs, K1ZM, recommends a "poor man's Beverage". If you have at least 150-200 feet of space, Jeff recommends you solder together a number of Slinky toys. These are available at outlets such as Toys-R-Us or Kay-Bee Toys. I'm told that RadioKit, Inc. in Pelham also has them. Pass a dacron rope through the center of the array to suspend it and tie the dacron off to trees. Along the length use dacron suspended in other trees to hold the array more or less horizontal to the ground. As with a regular Beverage, it is important to maintain constant elevation, and not follow ground contour. The antenna is terminated in the same fashion as a regular Beverage.

Several other antennas may work for you. The Receiving "EWE" Antenna, described in the February, 1995, issue of QST may be of interest. The 160-Meter Magnetic Loop Receiving Antenna may also be a possibility. These various antennas are described fully in the references cited.

Well, I hope perhaps I've piqued your interest in 160 meters and that we will have the opportunity to QSO there one of these days. Until next month…

73 es Good DX, de K7CTW

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