I have a homemade K9AY loop with the classic diode setup to pick direction
remotely. Unlike the classic switching scheme with Bias-T's, I use isolation
transformers at both ends to couple switching voltages into the coax. I started
with 1N4001 because they looked more than beefy enough.
This past summer I lost the diodes several times, I assumed due to thunderstorm
activity. Diodes failed shorted each time. Easy enough to fix. This time I put
in 1N4007's.
This past weekend I again lost the diodes, again failed shorted. No
thunderstorm activity but maybe induced signals from my TX antenna? Big RTTY
contest with the amp on.
I also had built a little switching matrix of transistors and foot switches
inside the shack to let me pick direction with a footswitches. Those
transistors have blown several times too. Again first time I assumed
thunderstorm but not so sure anymore.
So obviously there is some voltage differential zapping these simple low
voltage switching devices. Thing is, the switching network is completely
galvanically isolated at the antenna end. Confirmed with ohmmeter and HV
supply. Unlike the classic K9AY design, I use isolation transformers at each
end to couple the switching voltages in.
So what is killing these simple semiconductors? Thinking about removing all
semiconductors and running independent switching wires.
Tim N3QE
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Topband Reflector
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