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R: Orbit 250 apogee



Hi all,

In order to get all of us the same performance on receiving AO40 signals it
is not mandatory to use all the same 0,5 dB NF downconverter and 24 dBi
antenna but it is mandatory to have a receiving system with the
same constant G/T

As an example,supposing i have a System Overall Noise NF=0,5 dB ,than the
Noise Factor is 10E0,05=1,12
and the equivalent Noise Temperature is (1,12-1)x290= 35 kelvin
24 dBi antenna gain equals to 10E2,4= 251 in power factor
Than my  ratio G/T=251/35 = 7,17=8,5 dB

If my friend like to get  my same receiving performance,and his antenna is a
2 meter dish with 32 dBi gain =1585 in power factor at 2400 MHz,
than his receiver Noise Temperature T for the same G/T  is
T=1585/7,17=221 kelvin from wich the Noise Factor F is
F= (221/290)+1=1,76  and NF= 2,46 dB

Now my friend  can use a very poor  downconverter with 2,46 dB of Overall
Noise Figure and  have my same receiving performance ! !

The G/T constant should be supplied by  AMSAT as it was for OSCAR-10 and 13

If designing our receiving system we all accomplish things in order to meet
the G/T constant every one will be happy

73 de i8CVS Domenico






----- Original Message -----
From: Mike and Donna West <wl7bqm@gci.net>
To: Estes Wayne-W10191 <W10191@motorola.com>
Cc: <amsat-bb@AMSAT.Org>
Sent: Thursday, May 17, 2001 4:40 AM
Subject: Re: [amsat-bb] Orbit 250 apogee


> Wayne wrote.....
>
> "Ideally we would all get 0.5 dB NF downconverters and 24+ dBi antennas,
> plus
> precision rotors to handle such a narrow antenna beamwidth.  But most of
us
> don't have all that, and should we really need that with a 50W transponder
> and high gain antennas?  Maybe the current LEILA-controlled "power per
user"
> is appropriate for some time in the distant future when there are 100+
> signals on the transponder.  But it doesn't seem reasonable now when there
> are few users and most of us are struggling to hear the satellite."
>
> So are you saying that we should allow excess power as normal because we
> *can't/won't* build better receiver-systems?????
>
> Let me know RIGHT NOW before I go and do ONE HELL of a lot of work
improving
> my receiving ability and I can work the bird now....... (I would like to
> have the EXTRA 15 to 20 degs of elevation that you guys get over us here
in
> Alaska)........I'll take down the Meyers and take the preamp off the
> Drake...............................Put up a vertical and run 150
> watts....Hell, I'll buy a kilowatt amp..... It's OK....only a few
operators
> on right now.....
>
> ALL THESE YEARS OF  """YOU CAN"T WORK THEM IF YOU CAN"T HEAR THEM""""""" I
> love this new way of doing things....The easy way out.........
>
> I don't want to ruffle feathers but I'm not sure if that way of thinking
is
> good for ham radio....
>
> de mike
> WL7BQM
> BP40
>
>
>
>
>
>
>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>




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