The antenna end of mine, looks very similar to PG0A/PA3FYM implementation,
drawn at
http://remco.org/wordpress/wp-content/uploads/2008/01/pg0a-k9ay-small.jpg
Uses an isolation transformer (not an autotransformer) and provides galvanic
isolation between antenna, antenna ground rod, and the coax.
I do not use LED's in mine, I just use regular diodes, and these are the diodes
that are blowing. I'm starting to believe that it's during RTTY contest
weekends when I'm on 10 a lot, that the diodes are blowing, and I think Tom's
suggestion about bypassing effective for 10M (not just 160M) may be most
relevant.
Tim N3QE
-----Original Message-----
From: kd9sv [mailto:kd9sv@comcast.net]
Sent: Friday, November 15, 2013 7:43 AM
To: Shoppa, Tim
Subject: RE: Topband: Blowing diodes on relay switches
Tim can you share a schematic of what you are doing? I don't see how it is
possible to couple DC voltage through a transformer...de gary
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Shoppa, Tim
Sent: Friday, November 15, 2013 7:34 AM
To: 'topband@contesting.com'
Subject: Topband: Blowing diodes on relay switches
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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Topband Reflector
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