Topband: To clamp or NOT...that IS the question

[Charlie Cunningham]

Not lkely, I think, Jim. I presume the FET would have some significant bias
( perhaps 5-12 V) on its drain when it is not conducting, so relatively
large signals are not very likely to produce non-linearities and intermod or
cross modulation as the diodes might. My TCW.

Of course on could also add an additional relay (perhaps mercury wetted)
right at the RX port to clamp it when thetX is enabled.

73,
Charlie, K4OTV



-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of James
Rodenkirch
Sent: Friday, January 17, 2014 12:38 PM
To: Top Band Contesting
Subject: Topband: To clamp or NOT...that IS the question




A friend of mine is building me a switching arrangement with a reed relay to
switch between my transmit antenna and a receive delta loop to the one
antenna input for my Ten Tec Jupiter (I operate at QRP levels for contests).
As an added measure of protection for the KD9SV low noise pre-amp I use with
my 160/80 delta loop antenna, he believes clamping the RX antenna port or
shunting to ground during TX sounds like a nice thing.  But, he's seen
arguments that clamping receiver input with diodes degrades the receiver
performance. He find this believable, but I don't know how true it is, e.g.,
he knows KD1JV claims his RX performance is achieved by using 2N7000 FETs to
do T/X switching.
He has a bunch of 2N7000 and will probably use one to turn on the relay.  He
can turn on another one along with the relay driver that will shunt the RX
antenna port to ground but he wonders if that would degrade receiver
performance.
Thoughts?  72/72, Jim Rodenkirch K9JWV

 		 	   		  
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