Two years ago, I put up a 20m, end-fed half-wave antenna. It wasn’t a terrific performer, but it worked OK, and I was able to make contacts on 20m.
Basically, it’s a 33-ft. piece of wire connected to a matching network, made up of a toroid and a capacitor, as shown in the figure at below. The inductor is a toroidal inductor, and the capacitor is made from a length of RG-174 coax, as shown in the figure below.
A month or so ago, the antenna started acting funny. While transmitting, the power would fluctuate, not wildly, but noticeably. Thinking it might be the coax, I took my dummy load outside and connected it to the coax, but that checked out OK.
The next step was to check the matching unit. I had built the matching network in a waterproof box, or so I thought. When I opened the box, there was water inside it. Water had apparently gotten in around the screws holding the SO-239 to the box. I dried it out, replaced a rusty nut and bolt, and when I put it back together, sealed up the SO-239 with silicone.
That still didn’t do it, though. I was still getting the erratic behavior. Today, I practically rebuilt the entire antenna, aside from rewinding the toroid and making a new coax capacitor, but it’s still acting weird.
I guess my next step is to make a new capacitor. I suppose some water could have wicked up into the braid, compromising it. That seems kind of far-fetched though. At this point, I’m open to any other ideas you guys might have.
Walter Underwood K6WRU says
Water in the coax seems very likely to me. That would throw things off.
k8gu says
I agree with Walt that it’s a real and likely possibility that you have water in your coaxial capacitor. I’m not particularly enthusiastic about coaxial capacitors for this reason and the fact that lumped HV caps are readily-available and reasonably-priced.