[amsat-bb] Special AMSAT dinner
bruninga at usna.edu
Fri Sep 8 15:25:26 PDT 2006
Three years from now when we have to suffer from a new round of
comlaints about 2.4 GHz QRM interfering with the P3E Sband
downlink, we could have a special AMSAT dinner. The main entrée
might be crow.
I can attest that S-band for us, even with a 4 foot dish is
quite unuseable. It -was- useable when AO-40 was in orbit. We
used it for demonstrating sat-coms to students. Then we used
the same dish to "see" the noise temperature of the COLD SKY,
then the BUILDING and then the SUN. It was a nice lab showing
receiver noise temperature.
But even last year, we had to abandon that lab completely.
There is no way our receivers could even come close to hearing
the noise floor any more. The LANS and wireless cosumer devices
just add too much noise to the band. The interesting thing is
that you usually can't hear it. Maybe a pop now and then, but
the overall noise floor is just higher. So someone that turns
on his S-band receiver and doesnt "hear" anything, doesnt
necessarily prove a quiet location. The question is, whether he
can still hear a low enough noise floor so he can hear the sun
or even ground noise compared to cold sky. But even that is
hard. Pointing towards the horizon to hear the 300K noise of
the ground is usually pointeless because that is where all the
2.4 GHz QRM is, and so it goes way up anyway...
Just some thoughts..
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