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@telenet.be To: Andy Brian mailto:briaandy@gmail.com Cc: amsat-bb mailto:amsat-bb@amsat.org Subject: Re: [amsat-bb] RS-44 VU noise from TX Message-ID: mailto:1647041245.475312887.1590345807957.JavaMail.zimbra@telenet.be Content-Type: text/plain; charset=utf-8

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