[amsat-bb] RS-44 VU noise from TX

[tjschuessler at verizon.net]

When I started setting up to the 145 up 435 down satellites, I experienced
this issue badly.  The best solution I found was to use two separate
Diplexer to feed my Arrow on a tripod.  I ended up using a triplexer for the
2 meter side and a diplexer for the 70CM side.  The dual filtering seems to
clean up all the third harmonic crud.  Some folks recommend a 50 Ohm
terminator for unused ports but I most of the time don't use one. I put my
preamps on the inside of the diplexers as filters because the loss is small
on the diplexer and filtering before the preamp will go a long way.
Limiting power is also a help.  Most of our linear birds are pretty
sensitive so keeping our transmitters down to a very low transmit output is
best for the satellite

Now the comment was relating to SDR devices for the RX side, depending on
what you have, some of these have very poor RF shielding so that in itself
is a real problem

Tom Schuessler, N5HYP
EM12ms
_______________

Message: 
Date: Sun, 24 May 2020 20:43:27 +0200 (CEST)
From: mailto:on4cjq at telenet.be
To: Andy Brian <mailto:briaandy at gmail.com>
Cc: amsat-bb <mailto:amsat-bb at amsat.org>
Subject: Re: [amsat-bb] RS-44 VU noise from TX
Message-ID:
	
<mailto:1647041245.475312887.1590345807957.JavaMail.zimbra at telenet.be>
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Hoi,

Instead of putting a diplexer as filter( best is to use 1 per band), if you
have the possibilty to make stuff your own, just 'split' a diplexer by
making an LPF (low pass filter) at the 2m antenne and a HPF ( high pass
filter) at the 70cm antenne. Or find some to buy (MINI CIRCUITS maybe?).
This way you have a filter at both antennas. Mostly a diplexer is used only
on one antenna, while the other diplexer port is closed with a small dummy
load.
Keep in mind the tx-pwr!

Best 73's

Jerry,ON4CJQ