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

[John B. Stephensen]

They're lucky not to live in a restricted area. I had to live with the 1 kW 
EIRP restriction for many years. 2 meter or 13 cm uplinks eliminate the 
problem.

73,

John
KD6OZH

----- Original Message ----- 
From: "i8cvs" <domenico.i8cvs at tin.it>
To: "John B. Stephensen" <kd6ozh at comcast.net>; "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 21:35 UTC
Subject: Re: [amsat-bb] Fw: Re: NASA's American Student Moon Orbiter...


> 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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>
>
>
>