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

[John B. Stephensen]

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
>
>
>
>
>
>
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