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Re: Downlink sensistivity, preamps and attenuators, LEILA



I can easily hear it with a 4.5 foot dish and a 1.0 dB NF preamp. It is
really apparent when there is a lot of QSB. If you go to a clear frequency
it sounds like waves in the ocean.

Pieter


----- Original Message -----
From: "Douglas Braun & Nadia Papakonstantinou" <doug@dougbraun.com>
To: "Charles Suckling" <csuckling@nhlab.demon.co.uk>; <amsat-bb@AMSAT.Org>
Sent: Friday, May 18, 2001 12:07 PM
Subject: Re: [amsat-bb] Downlink sensistivity, preamps and attenuators,
LEILA


> 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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