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@comcast.net To: "i8cvs" domenico.i8cvs@tin.it; "AMSAT-BB" amsat-bb@amsat.org; kl7uw@acsalaska.net; "Joe" nss@mwt.net; "G0MRF David Bowman" g0mrf@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@tin.it To: "AMSAT-BB" amsat-bb@amsat.org; kl7uw@acsalaska.net; "Joe" nss@mwt.net; "G0MRF David Bowman" g0mrf@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@aol.com To: nss@mwt.net Cc: domenico.i8cvs@tin.it ; kl7uw@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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