A couple of years ago, my 40m dipole came down when an ice-laden tree branch fell on it and broke one of the elements. Since I didn’t want to be off the air, I threw up an 85-foot random-wire antenna. After playing around with it for a while, I actually got it to tune up on 80m with a small, manual tuner that was designed to tune random wires, and made some contacts.
I wanted to try to get the wire to work with the SGC-239 automatic tuner that I have, but I never got it to work properly. When I asked on the SGC mailing list about this, the consensus was that I needed a counterpoise longer than the driven element.
Well, seeing as how it’s now time to get back on 80m, I thought I’d add some wire to the counterpoise and see if I could get it to work. First off, I had to get the wire back up into the trees. I had hastily thrown the wire up there and secured it with some cheap twine. This summer, the twine gave out, and the wire came down.
What should have taken about five minutes to do, actually took about 45 minutes. The wire snagged on a dead branch, so I had to trim that. Then, I lost the tennis ball that I use to throw ropes up into trees. That took about 15-20 minutes to find. Fortunately, I did get the wire back up in the air before dark.
Unfortunately, the wire didn’t tune up well at all on 80m. About the lowest SWR that I could manage was 2.0:1. This evening, I went out there and disconnected the piece of wire I added on Sunday. Now, it tunes like a champ again.
As I’ve said before, I’m no antenna genius, but this is a result I did not expect, but it obviously affected the tuning. Any theories? Is there any way to predict how long a counterpoise one needs with a random-wire antenna?
I just consulted an old edition of the ARRL Antenna Book, and here’s what they have to say:
When operating with a random wire, it is wise to try different types of grounds on the various bands, to see which will give the best results. In many cases, it will be satisfactory to return to the transmitter chassis for ground, or directly to a convenient water pipe (NOTE: This isn’t legal according to the NEC.). If neither of these works well (or the water pipe is not available), a length of No. 12 or No. 14 wire (approximately a 1/4 wavelength long) can often be used to good advantage…..Run it out and down the side of the house, or support it a few feet above the ground if hte station is on the first floor or in the basement. It should not be connected to actual ground at any point.