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Re: Topband: Blowing diodes on relay switches

To: kd9sv <kd9sv@comcast.net>, "topband@contesting.com" <topband@contesting.com>
Subject: Re: Topband: Blowing diodes on relay switches
From: "Shoppa, Tim" <tshoppa@wmata.com>
Date: Fri, 15 Nov 2013 14:32:56 +0000
List-post: <topband@contesting.com">mailto:topband@contesting.com>
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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