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Re: [TenTec] Isolation of diode T/R Switch on Corsair

To: tentec@contesting.com
Subject: Re: [TenTec] Isolation of diode T/R Switch on Corsair
From: Joe White <jwhite001@bellsouth.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Tue, 9 Jun 2009 06:26:52 -0700 (PDT)
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
Thanks for the replies, gentlemen.

In answer to your questions,
I made the measurements with a 10X probe on the transmitter running 100
watts out (200V p-p).  Leakage amounts were on the order of 0.2 to 1.3V
p-p, with the higher values observed at the higher frequencies.  This lower 
isolation at the higher frequencies
could be attributed to the effects of leakage on the measurement, but
perhaps more likely is that residual capacitance of the diodes simply
makes the diode switch less effective at higher frequencies.

Because of the high signal levels, noise
should not be a factor.  

to 60 dB sounds like pretty good isolation for a two diodes cascaded
followed by a shunt transistor, so it does sound like the output diode
switch is doing it's job.  I was more concerned that if the leakage
gets significantly above the 1.3V level that it could get close to the
biasing level of the input PIN switch on the low-level driver board,
but since that bias is about half of the 12V supply, maybe it's not an
issue either.  

Anyway, I
was hopeful that someone might have actually measured that leakage at
some point in making the same repair that I was making, and if the
measured values that I was seeing were typical of a properly
functioning Corsair.  They certainly seem to be, ..but there's always that 
nagging doubt that somethings going to blow when I push up the power since it 
did once before.

Thanks for taking the time to read and reply.

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