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Re: Orbit 250 apogee



We can make estimates of what is required given current data. In 1999, AMSAT
published a requirement for a G/T of 0.53 with a squint angle of 0 and the
S1 transmitter. A 16 dBic gain antenna (16-turn helix) and 1 dB NF receiving
system would generate this level of performance if there is no coax between
the preamp and antenna. If a converter with a 5 dB NF and no preamp is used,
9 dB more of antenna gain is required. The only reasonable way to acheive 25
dBic of gain is a 3.5 foot dish with a circularly polarized (helical) feed.
A linearly polarized (dipole) feed would require a 5-foot reflector. If the
next orbit change is successful and the momemtum wheels are used to acheive
a constant squint angle of 0 then these parameters should be OK.

In the mean time, according to data published on this mailing list, the S2
transmitter has 2 dB less EIRP and the S2 downlink antenna gain is estimated
to be down 3 dB at a 9 degree squint angle. To get the level of performance
that AMSAT was predicting a G/T of 1.67 is then required for operation while
the satellite is spin-stabilized. A 0.8 dB NF and a 20 dBic gain antenna
will accomplish this. 20 dBic requires 3 16-turn helices, a 2 foot dish with
a circularly-polarized feed or a 3-foot dish with a dipole/reflector feed.
More gain and/or a lower noise figure allows operation at greater squint
angles.

73,

John
KD6OZH

----- Original Message -----
From: "i8cvs" <domenico.i8cvs@tin.it>
To: "Mike and Donna West" <wl7bqm@gci.net>; "Estes Wayne-W10191"
<W10191@motorola.com>
Cc: "AMSAT-BB" <amsat-bb@AMSAT.Org>
Sent: Friday, 18 May 2001 13:28 UTC
Subject: R: [amsat-bb] 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
> >
>
>
>
>
> ----
> 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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