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Topband: Transmit antenna de-tuning relay.

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Subject: Topband: Transmit antenna de-tuning relay.
From: Greg Chartrand via Topband <>
Reply-to: Greg Chartrand <>
Date: Sat, 23 Mar 2019 17:35:23 +0000 (UTC)
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 The best way to isolate the TX antenna for receiving is to have it float above 
ground. The worst means is grounding the antenna. The grounded antenna will 
re-radiate any noise it captures rendering your RX antenna useless. It only 
takes a few PF to ground to make a TX antenna your principal noise source so 
keeping that in mind, deploy the relay(s) such that the antenna sees no ground.
In my case, I have a center loaded vertical, it connects to a L network 
matching circuit; the isolation relay opens the wire going to the vertical so 
it floats well above ground. It can get tricky is you have a grounded shunt fed 
tower, however, I found floating the shunt wire works as well as anything.
The best test for finding the best isolation strategy is to take an AM radio 
tuned as high as it can go and put it in as close as you can to the vertical. 
You should hear the re-radiated noise make the radio blast noise. Now you can 
test grounding (if you don't believe me), floating,and even de-tuning. BTW I 
could never get de-tuning to work as well as floating.
Good luck!Greg W7MY
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