Re: [amsat-bb] Amateur radio module on commercial Geo Sat?

[tlang@xxxxxxxxxxxxxxxxxxxx (Tony Langdon)]

Hello Phil!

19 Dec 00 22:18, you wrote to All:

 PK> antennas. That's one of the reasons Qualcomm invented IS-95 CDMA.
 PK>
 PK> Things are different in a single-beam satellite environment with
 PK> directional antennas on the ground.  You don't have significant
 PK> interference from other satellites on the downlink or from users of
 PK> other satellites on the uplink.  Each user on a given satellite
 PK> adjusts their uplink timing so that everybody arrives at the right
 PK> time at the satellite. Once that happens, it doesn't matter that there
 PK> are different propagation delays to the various stations on the
 PK> downlink, as all the signals coming out of the satellite are delayed
 PK> together by the different propagation delays.

OK, I get the general gist of the idea.  There's still a few details to be
resolved in my mind, but the basic idea makes sense.

On the microwave bands, the assumption that the ground station is using a beam
antenna would be indeed valid, may not apply on lower frequencies, depending on
the details (but since we're talking about 1,2 and 2.4 GHz, this is a moot
point.

 PK> My thinking is that the satellite would periodically inject a frame of
 PK> telemetry into the transponder, and this frame would serve as the
 PK> timing reference for the uplink transmissions. The individual stations
 PK> would adjust for the uplink delay from the satellite orbital elements
 PK> and the known station location. The satellite could broadcast its own
 PK> orbital elements as part of the telemetry message, just as GPS does.
 PK> The ground station location could be entered manually by the user, or
 PK> determined automatically from a GPS receiver. The GPS receiver would
 PK> also provide time for the accurate propagation of the orbital
 PK> elements.

So, basically a case of using GPS to measure positional differences and time
delays?  These days, quite feasible, given the lowish cost of surplus GPS
engines that can be obtained from time to time.

Interesting idea all round.

Tony, VK3JED

.. Mr Worf, scan that ship." "Aye, Captain ... at 300 DPI ?
--
|Fidonet:  Tony Langdon 3:633/284.18
|Internet: tlang@freeway.apana.org.au
|
| Standard disclaimer: The views of this user are strictly his own.


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