On 07/20/2014 06:13 AM, Simon Brown wrote: > John, > > If both side have good Doppler correction then it can be done, but you have > to choose the correct mode as there are other issues even if the Doppler > correction is perfect, especially when the range is changing at its maximum, > for example as the satellite passes overhead.
Correct, but Doppler actually gets much easier to deal with as the data rate increases. What matters is the *ratio* of the Doppler to the data rate (actually the channel symbol rate, which is usually higher). At the very high rates possible from LEO on the microwave bands, Doppler on a BPSK signal can be easily tracked by a Costas loop even without orbit prediction steering (though it's still a good idea). E.g., a relative velocity of 3 km/s at 10 GHz is a Doppler of 100 kHz, considerably less than the symbol rates possible from LEO with even small transmitter powers and antenna gains. Compare this with the numbers for current amateur satellites on VHF and UHF. --Phil _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
