Tiny Elephant's Contest CornerThe Latest Contest News -
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Tiny Elephant's Contest CornerThe Latest Contest News -
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For those of you new to ham radio, a Beverage antenna (also known as a wave antenna) has been around almost as long as ham radio itself. The Beverage antenna is a directional receiving antenna named after Harold Beverage who investigated the receiving properties of long wire ground antennas and documented his findings in 1923. Old Harold's antenna concept is nice and low-tech: a wire at least half a wavelength long at the frequency of interest and terminated in its characteristic impedance. The termination is what gives the antenna it directivity while its low height and horizontal orientation reject a lot of manmade noise that tends to be vertically polarized. One fortuitous outcome from Beverage's research was that the antenna performs well at a small fraction of wavelength above the ground, making it ideal for erecting antennas for low frequencies. This was especially welcome news in 1923 when amateurs were allowed to operate lower than 160 meters. It took on even more significance when one realizes that Henry Ford only built cars and trucks and the "cherry-picker" was years away.
The Beverage antenna spawned several versions of receiving antennas, including the 2-wire Beverage, also known as the Steerable Wave Antenna that can be switched to receive in either direction. Vic Misek, W1WCR, has done an excellent job compiling the technical characteristics of the Beverage antenna in his book, The Beverage Antenna Handbook. Thanks to Vic's efforts, I was able to figure out what kind of Beverage I could put up and what kind of performance I could expect.
The first thing for a Beverage antenna is ROOM. This was not a problem in 1923 when 15 miles from Manhattan was in the country. In 2000, however, having an 800- 1000 foot run on your property means lots of money or skill at buying a home backing up to wetlands or a forest preserve. When I moved here 15 years ago, I had over 60 acres of woods behind me. The woods have since given way to 16 large homes. There is still a stretch of woods north of me that is not supposed to be developed because the hillside is too steep. Hmm, the land slopes toward the Northeast, just fine for Europe.
I trekked through the area several times to site how I could run an antenna. The Beverage performs best when mounted in a straight line at a uniform height over uniformly conductive ground. The ham who lives next to a salt marsh with a multi- wavelength Beverage has it made for DX. The best I could hope to do, however, was to hang my antenna about the same height above ground from trees as I played it out.
Since I had more wire than room to string it, I decided to start at the far (termination) end and run it up to the feed end. The impedance of a Beverage is largely a function of the wire diameter and its height above ground. For my setup, this worked out to 535 ohms. Calculations in The Beverage Antenna Handbook show the impedance is not critical, varying less than 100 ohms for antenna heights of 6 to 20 feet. I used several 1500-ohm, 100-watt resistors in parallel connected from the antenna to a ground stake. A standard 560-ohm, 1/2-watt resistor would also work, but I happened to have the big ones around and got the benefit of more mechanical strength as well. I sloped the antenna for the first 30-40 feet from the termination to its normal height. The reason for the slope is to eliminate a vertical drop to the termination point, thus minimizing pick-up of noise.
Stringing the antenna in a straight line proved almost impossible since Nature does not plant trees the right way. I found myself repeatedly eyeballing the termination end where I started with where I hoped to end up. As I secured one section of antenna about 10 feet up, I pulled it taut to check it for straightness before working my up the slope to the next tree. Sometimes I had to go back and move to one side or the other of the previous tree in order to straighten out the antenna. When I got to the feed point, I again sloped the antenna down to the ground to a transformer box that contained a 9:1 toroidal transformer. I strung a couple pieces of coax to go from the feed to the shack.
Now the smoke test. I connected the antenna to a 1.8-4.0 MHz preamp in the shack that I got for this "round-to-it" project. I tuned the rig down to the low end of 80 and listened for some DX stations. I found that the antenna, without the preamp, was indeed much quieter than my quad, and the signals were also much lower. Switching the preamp on brought signals up to within 5 dB of the level observed on the quad. I noticed that the noise level also came up a lot more.
I switched to 75 and found a strong station from Ireland that would give me a good test. This time, the Beverage and preamp were about 5 dB better than the quad, although the increase in noise actually hurt readability. The Beverage seemed to be working but I could not get good data on the benefit of the preamp because of the noise. I was not surprised by the noise level because I was amplifying a signal after it traveled through 160 feet of coax with a splice in it and one piece that had been outside for years and even longer in the attic. It's a good bet my poor preamp has an noise figure almost as high as my IQ (well, maybe higher).
My initial tests confirmed that I was on the right path. My next step will be to install the preamp at the antenna and run a continuous piece of good coax to the shack. I also plan to experiment with varying the termination resistance to tune the antenna for 80 and 160. A good SWR won't change things much on a receive antenna, but a fraction of a dB could mean a completed QSO. I hope to have it operational by the time this gets to press so it’s ready for these coming contests:
73, de K2TE