Antenna Overview
Our property is only about 90 feet wide but happily it is 495 feet long, from east to west. This is plenty of room to run a short Beverage antenna for receiving on the low bands (160M and 80M).
I strung about 260 feet (estimated with Google Earth) of insulated wire along a chain-link fence, then through the woods to the bottom East end of the property.
This 260-foot length is close enough to the 270-foot length many expertssay is good for a short Beverage antenna. (See Gary K9AY’s page on the subject of Beverage length). The wire is anywhere from 4 to 7 feet off the ground, and dips and dives along its length — the East end is a long way down-slope from the feedpoint near the shack on the West end.
The antenna is unterminated, making it bidirectional — it hears from the East and West, and because it is short, it has wide lobes in both directions, which is very useful to me as this covers most of the U.S. and all of the most populous areas of the Pacific and Asia.
Why use a Beverage antenna? It is a simple antenna that really hears signals well, while removing a lot of noise.
The homebrew transformer
I estimated the impedance from the Beverage wire to ground at about 450 ohms. Feeding it with 50-ohm RG8X coax cable means I need to transform the 450 ohms to 50 ohms — which suggests a 9:1 transformer. Guys in the know (for example, Bill VE3NH) say if I use the correct binocular-core toroid, with 2 turns on the primary (at the coax side) and 6 turns on the secondary (at the Beverage side), I should be rolling in clover.
Well, I am rolling in clover. In 2008, I tried this arrangement using a junk-box binocular core of unknown specifications (other than it was a binocular core). I actually salvaged it from a TV 75-to-300 ohm coax-to-twinlead balun thingy. I knew it was probably the wrong ferrite material — likely 43 or other lower permeability, which would be more suited to higher frequencies such as VHF work — or need many times more windings to work well on 160M or 80M.
But I often ignore such details and so I gave ‘er 2 turns on one side, and 7 or 8 turns on the other side just to see if I could notice any Beverage-type benefits from the 260-foot-long wire I had strung up.
It worked — not great, perhaps, but it worked. Noise disappeared on 160M, not quite so much on 80M, and not at all on 40M (where signals seemed so attenuated as to not be useful at all).
In November 2009, I decided to do things properly and ordered a $35 RF Experimenters ferrite kit (Kit #4) from Amidon Associates. This is a great deal, containing four of the BN-73-202 binocular cores and dozens of other cores of various materials, sizes and formats (including a nice FT-240 toriod and wire to make a high-power 4:1 balun… this retails for $14 alone!). The kit arrived from California in five days by U.S. Postal Service.
Beverage vs. a 2-element 80M vertical array
Here’s how it sounds — these recordings were taken on the evening of November 17, 2009 UTC (around 8 p.m. Pacific time).
ZS2JX on 80M (.mp3 – 640kb) at 0400Z
The audio opens with the Beverage antenna, then to my 2-element 80M vertical array pointed due East (or a bearing of 90 degrees — about 30 degrees from where Peter is at 60 degrees azimuth from here). You’ll hear the signal clearly on the Beverage, then louder but with more noise on the vertical array.
I must note that Peter’s signal was unusually loud on this autumn evening…. the loudest I have ever heard him here. He uses a twin vertical array very much like mine.
KH6LC on 80M (.mp3 – 264kb) at 0500Z
The audio opens with KH6LC on the Beverage antenna, about an hour after Peter ZS2JX was recorded. You’ll hear when I switch to my 2-element vertical array pointed due West (almost exactly at KH6 from VE7). The difference in noise is dramatic — and it disappears again when switching back to the Beverage antenna.
