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[aprssig] 9600 doppler solution?

Wes Johnston aprs at kd4rdb.com
Wed Aug 31 13:50:57 UTC 2005


One of the problems with receiving PSAT2 9k6 on 70cm is the wider
doppler shift.  It just occurred to me that with the use of AGWPE
(probably mixw32 also), you can setup two sound cards in a PC, giving 4
channels of audio to decode.  Just program each sound card input to be a
9k6 modem and wire each to a FM receiver tuned to a slightly different
frequency.  Let's say we tune radio #1 437.970 MHZ , radio #2 437.975
and radio #3 437.980 all at a single site.  The PC will try it's best to
decode signals rx'ed on all 3 modems.  Perhaps when the doppler shift is
3khz, it'll decode on two of the three modems.  This also still leaves a
4th audio channel open to be a 1k2 receiver too.

We're using a setup like this at the NWS office in Columbia SC to
passively monitor 3 voice repeaters for mic-e data.

Wes




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