[amsat-bb] Re: Preamp protection

SV1BSX sv1bsx at yahoo.gr
Fri Sep 15 13:21:03 PDT 2006

 Hi Angel,

  BTW, I wondered about the same thing a few months ago and I found as
"Final Solution" the intended  (by Domenico, i8CVS) filter.
   However, I had 1-2 ideas and I believe that you can do it also  by using
2x "Quarter Wave" (Lambda/4) coaxial pieces and between of them  the two
antiparallel diodes. The coaxial pieces is possible to have any form, so the
circuit can be compact enough but I've no idea about the max. isolation of
this combination in dB. In other words I can't say under how much TX power
remains safe the pre-amp.
 Another approach is that, by replacing the 2 diodes with just a PIN diode.
With a sensitive RF-sniffer circuit, you can put a Bias-voltage onto
PIN-diode when you have
a faulty PTTand thus, the input-output of 2x "Quarter Wave line" produced
very high Z, protecting this way your pre-amp.

Good luck (without... smoke on your pre-amp !)

73, Mak SV1BSX

----- Original Message -----
From: "Angel Peláez, EA4DUT" <angelkilroy at yahoo.es>
To: <amsat-bb at amsat.org>
Sent: Friday, September 15, 2006 5:10 PM
Subject: [amsat-bb] Preamp protection

Hi everybody:

I'm looking for the schematic diagram of a preamp
protector against TX.
I know the impressive quarter wave design with square
brass stock and clamping diodes for 432 EME which
Domenico, I8CVS, described I don't remember where.
Rather I'm looking for something much compact as I
would like to use from VHF to above. I mean one of
these small boxes (RF diode clippers???) I see
sometimes on commercial pages which promises withstand
25W for a short period I'll appreciate any comment
about the issue.
Thanks in advance.

EA4DUT, Angel

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