To All, Solid State transmitters have white noise generated due to the changing I/O reactance as a function of the junction voltage of FET/BJT devices. Since both transmitters have low pass filters for harmonic suppression that also reduce white noise above the transmit frequency the Diplexer is most effective on the 70 cm side preventing white noise from blocking the 2M receiver. BTW Tubes do not have white noise.

Art, KC6UQH

-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Greg D Sent: Sunday, January 19, 2014 7:42 PM To: Jim Jerzycke; w4tas; 'AMSAT Mailing List' Subject: [amsat-bb] Re: 145 MHz signal blocking 435 MHz downlink

I know this has been answered before, but I forget. Given one Diplexer, is it better to put it on the Tx side to limit the 3rd harmionic going out, or better on the Rx side to limit the VHF fundamental coming in? Tony's diagram shows the later; I would have thought the former would be more effective (hitting the problem at its source).

Greg KO6TH

Jim Jerzycke wrote:

Yep, been using one of those for years!

I have a Sinclair Labs unit that provides 100dB rejection outside of the 2 Meter band.

Jim KQ6EA

On 01/19/2014 07:32 PM, w4tas wrote:

...

I would also suggest a low pass filter on the two meter transmitter. A diplexer will work well for this also. This will reduce the third harmonic which is causing your problem.

Good luck,

-----Original Message----- From: Jim Jerzycke Sent: Sunday, January 19, 2014 2:09 PM To: amsat-bb@amsat.org Subject: [amsat-bb] Re: 145 MHz signal blocking 435 MHz downlink

Buy a diplexer, and connect it as shown in the linked article:

http://www.amsat.org/amsat-new/articles/Mode-J/

I also tilt both of my Yagis so they're 45* to the boom, which makes them 90* to each other.

Yes, I lose some signal on terrestrial use, but ti helped cut the coupling, and desense, down quite a bit.

73, Jim KQ6EA

On 01/19/2014 06:56 PM, Gabriel - EA6VQ wrote:

...

Hi all,

I have a coupling problem in my station when trying to work FO-29. My 2m signal is completely blocking the 435 MHz downlink, and so I can't hear my signal off the satellite. I guess it must be something related to the distance between the two yagis. (I use the terrestrial horizontal yagis you can see at http://www.dxmaps.com/jm19hn.html ). With mode-B satellites there is no problem. I have tried it with two different 435 receivers, and it's exactly the same.

Anyone has had this problem o have an idea of the possible reason? And what is more important, of some way to solve it?

Thanks for any possible help.

73. Gabriel - EA6VQ

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Web-Site: HTTP://www.dxmaps.com VQLog 3.1 (build 78): HTTP://www.vqlog.com _________________________________________________________

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