Re: [amsat-bb] Downlink sensistivity, preamps and attenuators, LEILA

[Douglas Braun & Nadia Papakonstantinou <doug@xxxxxxxxxxxxx>]

Good point there.  Has anyone actually been able to notice the transponder
background noise level?  I would think that you would need a
pretty good system to do this.  I couldn't notice any difference
with my small helix.

I guess you could also check the noise level by QSYing a couple
hundred kHz, out of the transponder passband.  (Assuming that the
gain of your system does not vary over that frequency range).

Doug
NA1DB

At 11:05 AM 5/18/01 , Charles Suckling wrote:

>One last thought - transponder noise could be used as a useful low-level
>"beacon" for checking out your system.  If you can hear transponder noise,
>then you can be fairly sure your system is working reasonably well. If not,
>then you still have some way to go.  The ideal situation to aim for,  is to
>have enough transponder noise (say 10dB above your receiver noise floor) so
>that the limit on your receiver sensitivity is not your receiver's noise,
>but that from the satellite.  Improving your system beyond that is then not
>worthwhile.  
>
>Transponder noise can be checked by tuning to a clear frequency when the
>transponder is in operation  and moving the antenna off the satellite to an
>area of clear sky and looking for a change in receiver noise level (just
>like measuring sun noise). 

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