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RE: Downlink sensistivity, preamps and attenuators, LEILA





> -----Original Message-----
> From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> Behalf Of Douglas Braun & Nadia Papakonstantinou
> Sent: 18. toukokuuta 2001 16:08
> To: Charles Suckling; amsat-bb@AMSAT.Org
> 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).
>
This is true. Unfortunately. I'm not quite sure if I have right permission
to say that but all man-made, industrial etc signals are almost saturating
the uplink receivers. There are many detectable wide-band noise sources
also.
We are polluting the atmosphere much worse that we really thought.
Imagine a steady 10dB noiseground worsening Your receiving...
And You can't hear that noise at ground level in your location.

(sorry for misspelling and lousy language...)

-Jari OH3UW

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