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ALON/ALAT etc.



Hi Cliff,

I've received information regarding the telemetry system that is in use. I 
hope it will help answer a number of questions for those attempting to 
receive the S band telemetry.

First, thanks to Mike, OH2AUE and Peter, DB2OS for answers to some of my 
specific questions. Also Stacey, W4SM - Ken, N2WWD (great keps!) and Paul, 
VP9MU for posting info to the BB that's been very useful. (I hope I haven't 
forgotten anyone...)

There are 2 S-Band transmitters and 2 S-Band antennas on board AO-40. The two 
antennas are a 50cm dish with 18 dBi and Helix with 10 dBi. Both antennas are 
RHCP. The dish is fed with a phased cross dipole. The antennas are dedicated 
to a particular transmitter. S1 transmitter feeds the dish and S2 transmitter 
feeds the Helix.

We know that telemetry is being transmitted by the S2 transmitter (we can see 
this in P3T) so we can conclude that we're using the Helix antenna (because 
it's dedicated to the S2 xmtr). From my resource material, I find a 10 dBi 
Helix has a 3 dB beamwidth of 64 degrees.

With the information Stacey posted concening ALAT/ALON, we can now use our 
tracking programs to reasonably calculate the "squint" or "offpoint" of the 
antennas onboard the S/C.

One last piece of information that is very helpful is the frequency of the S2 
Transmitter. Michael provided "the MB was at 2.401,318 MHz during the launch
preparation tests in Kourou". So we have a starting point for calculating 
Doppler to help find the beacon. While I believe this is an excellent 
reference, we'll all have to look at our individual setups. Those of us with 
modified Drake converters by now are aware of the frequency drift of these 
units. I certainly am in Vermont! So being able to use our tracking programs 
for doppler calculations will not be an absolute. Even so, it will get us 
close.

At some point I'd love to have the EIRPc of the antenna/transmitter 
combinations so I could do some path loss calculations for fun........

Putting this information together, (antenna pattern, squint, doppler) we can 
now get a good idea of where and when we should be able to hear and hopefully 
decode the telemetry.

Happy New Year!

73,
Mike, N1JEZ
AMSAT #29649
Local Area Coordinator
"A closed mouth gathers no feet."
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