Wednesday, June 15, 2005

Antenna problem solved

Without the availibility of an antenna analyzer, I was able to figure out my antenna problem using a process I like to call "troubleshooting by elimination"; or otherwise known as common sense.

As I mentioned before, my Butternut HF9V went "deaf". I couldn't hear signals through it; or even more strangely, would stop hearing signals though it as soon as I applied RF energy to the antenna. Taking off the coax from the 75 Ohm matching stub; and hooking up my K1 and battery yielded plenty of signals. In my mind, that pretty much eliminated the antenna proper.

The next step was to remove the 75 Ohm matching stub for examination. The matching stub, as supplied by Bencher, is nothing more than a 15 foot length of RG-11 coax with a PL-259 on one end and two ring terminals on the other. One ring terminal is connected to the center conductor, the other to the shield. Examination revealed that the connection to the ring terminal for the center conductor was pretty badly frayed. The center conductor is multi-stranded wire and about 75% of the strands had broken. The logical step at this point was to replace both ring terminals and the PL-259 on the other end. A few minutes worth of work; and this was done. I trotted out to the antenna and installed my newly repaired matching stub. Unfortunately, the result was the same. The antenna was either deaf; or would soon go deaf after applying enough RF to send out a "QRL?".

The only left that could be bad was the coax itself. I kept on asking myself how coax could go bad. I have no idea. When I installed it, I had weatherproofed it pretty well to my own satisfaction; so water pentration was pretty much out. The only thing left to do at this point was to replace it, cross my fingers and to hope for the best. Thinking that maybe, just maybe, my two children might have damaged it by walking on it, stomping on it; or possibly by whacking it, I decided to go with something more robust. I had been using mini RG-8 because it's so flexible and easy to work with. This time I went with super low-loss "standard thickness" RG-8. Since I've gone totally QRP, I figured the less lossy cable could only be a benefit. I ordered 150 feet from the Wireman; and when the first opportunity for a small amount of free time presented itself, I installed it.

I went back down to the shack and hooked up the PL-259 to my antenna switch. I turned on the K2, switched on the HF9V and was greeted by plenty of loud signals which were quite comparable to the signals received by my G5RV. A simple little amount of switching between the two bore this out. The next test was to apply some RF and see what would happen. I found a clear spot on 20 Meters and sent out a "QRL?" in Morse, of course! To my relief, the antenna seemed to be whole again! This was quickly followed by a short QSO with another QRP station and the matter was finished.

Moral of ths story? If you're a married Ham with little children who play in your backyard; then do yourself a favor when it comes to picking out the coax for your antenna system. Forgo the more flexible cable and purchase the heavy duty stuff. Then maybe you won't be scratching your head someday, like I was!

73 de Larry W2LJ

No comments:

Post a Comment