[amsat-bb] Diplexer, Arrow ant, 2 handhelds question

[Stephen E. Belter]

Steve,

*If* the problem is 3rd harmonics from the 2 m transmitter, then what you did should have helped.  Adding a 50-ohm terminator might improve the attenuation of the 3rd harmonic.

A more common problem is that the 70 cm receiver can't handle the 2 m transmitted signal because the receiver doesn't attenuate the 2 m signal sufficiently.  (The AGC on the radio hears the 2 m signal, attenuates the whole 70 cm band, and you don't hear the satellite.)  By using the Arrow diplexer as a 2 m band reject filter, you may solve your problem.

For a better explanation see, Tony AA2TX's article here:
https://www.amsat.org/a-simple-desense-filter-for-mode-j-satellites/

So try your experiment again, but connect the antenna end of the diplexer to the 70 cm antenna and the 70 cm radio end of the diplexer to your receiver.

73, Steve N9IP
--
Steve Belter, seb at wintek.com



On 3/26/19, 12:18 PM, "AMSAT-BB on behalf of skristof at etczone.com" <amsat-bb-bounces at amsat.org on behalf of skristof at etczone.com> wrote:

    Today, on the SO-50 pass, I tried using the Arrow diplexer (duplexer?)
    to enable full-duplex using two handhelds. As most on this forum know,
    if you use two handhelds with the Arrow antenna, the third harmonic of
    the 2m uplink will desense the 70cm handheld, so you can't hear
    yourself. 
    
    So, I hooked up what is normally the antenna end of the diplexer to the
    2m uplink radio and the 2m radio end of the diplexer to the 2m part of
    the Arrow antenna. My hope was that this would suppress the third
    harmonic of the 2m uplink enough so that it wouldn't desense the 70cm
    handheld. The 70cm radio end of the diplexer was left unconnected. 
    
    It didn't seem to work. I made contacts but I still didn't hear myself
    on 70cm. 
    
    Just wondering if anyone else has tried this and what results you got. 
    
    Steve AI9IN 
    
    EM79ji
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