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Re: Amateur radio module on commercial Geo Sat?



>what if it was a SSB microwave only bird [1.2g and 2.4g] with two 
>transmitters and two receivers on each band? One a 1.2g uplink with a 2.4g 
>downlink. The second system with a 2.4g uplink and a 1.2g downlink. Each 

The 1.2 GHz band is available only for uplinks; it cannot be used in
the space-to-earth direction. 2.4 GHz is available in both directions,
but it is increasingly susceptible to terrestrial interference from/to
IEEE 802.11 wireless LANs. In the US, 802.11 channels run from 2412
MHz to 2462 MHz in 5 MHz steps, and the modulation is BPSK at 11
megachips/sec. There's obvious potential here for problems on the
lower channels.

SSB wouldn't make a whole lot of sense here. Coded digital modulation
(possibly carrying compressed digital voice) would allow much more
efficient use of ground station and transponder RF power and make
automatic doppler steering much easier. If modulation with a constant
envelope is chosen (e.g., BPSK, QPSK, MSK, 8PSK, etc) and the channel
is shared using time-division multiple access, then the transponder
can be hard-limiting. This allows significantly greater DC->RF
conversion efficiencies than can be attained with linear transponders.

Phil



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