30 August 2007

Coax Change on the Beam

Last weekend I continued the antenna work theme by doing some maintenance on my own setup. I have a 3-element 4-band beam on a 30-foot tower that has been giving some poor SWR readings lately. I decided to start with the coax since the line that was up there was 12-year old Radio Shack RG8, and the Tucson sun and monsoon rains can really wreak havoc on just about anything.
I had a couple of lines of Times Microwave LMR400 laying up on the roof, attached to a VHF beam that is currently out of service, so I decided the easiest approach would be to just swap the lines. I climbed the tower and it took me about an hour to make the changeout. While I was up there I noticed that the fiberglass insulators used on the Cushcraft antennas (I also have a small VHF/UHF vertical) were really trashed.
Anyway the change in transmission line seems to have helped quite a bit but I still have an unacceptably high SWR on 10 and 15 meters. 20 and 40 are just fine. I'm guessing there is a problem with the traps but it's going to be a big job to repair or replace the antenna.
It's a bummer that while the antenna is arguably the most important part of any ham radio installation, it's also the most difficult to maintain.

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