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Topband: Re: Back-to-Back Diodes

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Subject: Topband: Re: Back-to-Back Diodes
From: (Tom Rauch)
Date: Thu, 12 Sep 2002 20:11:00 -0400
> It seems to me that this would generate tremendous amounts of harmonic
> energy when being driven by a strong local signal.  If there were more
> than one strong signal, lots of mixing products would be the result. 
> Is there some reason I'm overlooking why this wouldn't be a problem?

Good point by Ward. 

It certainly can be a problem. Power detectors or clamps in RF 
switched devices can even cause RFI and TVI. For example, the TR 
switching diodes in some imported VHF amplifier actually cause the 
PA's to grossly fail FCC harmonic restrictions when the amplifiers 
are on standby and simply passing transmitter RF!

At the very least, diodes should be shunted by a resonant circuit for 
the band being used. Better yet, the system should be checked for 
harmonics and spurious signals if the antennas are close.

PIN diodes with long carrier lifetimes held solidly into clamping 
would be a better choice for across-the-antenna clamps.
73, Tom W8JI 

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