[amsat-bb] Re: Fw: Re: NASA's American Student Moon Orbiter...

[i8cvs]

Hi John, KD6OZH

There are many 432 MHz EME stations in USA and probably using big dish
(33 ft) in the range of 30 dBi gain with a lobe of 5 degrees at -3 dB do not
create interference to PAVE PAWS when the dish is aimed toward the moon.

73" de

i8CVS Domenico

----- Original Message -----
From: "John B. Stephensen" <kd6ozh at comcast.net>
To: "i8cvs" <domenico.i8cvs at tin.it>; "AMSAT-BB" <amsat-bb at amsat.org>;
<kl7uw at acsalaska.net>; "Joe" <nss at mwt.net>; "G0MRF David Bowman"
<g0mrf at aol.com>
Sent: Sunday, July 06, 2008 2:24 PM
Subject: Re: [amsat-bb] Fw: Re: NASA's American Student Moon Orbiter...


> UV is a problem as hams in much of the U.S. are limited to 1 kW EIRP on 70
> cm. The military is the primary user of the band. Recently, some repeaters
> near PAVE PAWS sites have had to reduce power to 5 W due to interference
> with the return signal from the 4 GW EIRP RADAR.
>
> 73,
>
> John
> KD6OZH
>
> ----- Original Message -----
> From: "i8cvs" <domenico.i8cvs at tin.it>
> To: "AMSAT-BB" <amsat-bb at amsat.org>; <kl7uw at acsalaska.net>; "Joe"
> <nss at mwt.net>; "G0MRF David Bowman" <g0mrf at aol.com>
> Sent: Sunday, July 06, 2008 08:53 UTC
> Subject: [amsat-bb] Fw: Re: NASA's American Student Moon Orbiter...
>
>
> > ----- Original Message -----
> >  From: G0MRF at aol.com
> >  To: nss at mwt.net
> >  Cc: domenico.i8cvs at tin.it ; kl7uw at acsalaska.net
> >  Sent: Saturday, July 05, 2008 1:21 AM
> >  Subject: Re: [amsat-bb] Re: NASA's American Student Moon Orbiter...
> >
> >
> >  Hi Joe.
> >
> >  Looking at 70cm up and 2m down, Dom has shown the 2m path can be
achieved
> > with a 13dB gain antenna on the ground and 10 Watts on the satellite.
> > That's a very small bandwidth transponder
> >
> >  For the uplink, it's not quite as easy.
> >  I've just run a link budget calculator and it looks like you need about
> > 80 Watts and 20dB of antenna gain on 70cm. That produces around 5000
Watts
> > ERP (allowing for losses)
> >
> >  As Dom pointed out, you dont just need a signal thats just above the
> > noise level at the satellite. Up there you need enough of a signal at
the
> > receiver so that the satellites transmitter can generate a decent amount
> > of power on 2m.
> >
> >  The 5kW ERP generates a signal around 16dB above noise at the
satellite.
> > With luck, that will be sufficient to produce enough power on the 2m
> > downlink.
> >
> >  Of course there are a lot of variables and 'detail' . but 5kW  ERP up
and
> > a 13dB gain antenna on the downlink are 'In the ballpark' for a minimal
> > working U/V system.
> >
> >  Thanks
> >
> >  David
> >
> >  Hi David, G0MRF
> >
> >  Looking at the specifications of AO40 I found that at 435 MHz the
> > equivalent noise temperature of the RX is
> >  TN (k) =  500 kelvin
> >  The Prx (23) i.e. the power needed by the receiver to develope a signal
> > of 23 dB over the noise is -145 dBW
> >  The 435 MHz satellite antenna gain is 14 dBi
> >  It is not specified the transponder output power with a S/N=23 dB
because
> > it depends on what transponder is intended to be used for the downlink.
> >  Probably -145 dBW at the RX input is the power needed to get a S/N = 23
> > dB at the IF input before to be switched by the matrix to different
> > transponders.
> >
> >  By the way the attenuation earth to moon at 435 MHz for 400.000 km is
197
> > dB and going back to calculations
> >  we get :
> >
> >  TX power at 435 MHz on earth........................  + 20 dBW (100 W)
> >  435 MHz antenna gain on earth ....................... + 18 dB
> >
> >  -----------------
> >  EIRP of the ground station................................ + 38 dBW (
6.3
> > kW)
> >
> >  Attenuation 435 MHz for 400.000 km ..............  -197 dB
> >
> >  ------------------
> >  Power received on a 435 MHz isotropic........... - 159 dBW
> >  antenna at a distance of 400.000 km
> >  Satellite antenna gain ......................................... + 14
dBi
> >
> >    ------------------
> >  Received power at RX input for S/N=23 dB....   - 145 dBW
> >
> >  It seems that both calculations match and 5 kW to 6 kW EIRP up on 70 cm
> > and 13 dBi antenna gain on the 2 meters downlink are a minimum necessary
> > provided that the satellite antennas orbiting around the moon are
> > constantly directed toward the earth but this is a very difficult task.
> >
> >  73" de
> >
> >  i8CVS Domenico
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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