[amsat-bb] Signalink for 9600 baud (possible Doppler tuning Failure)
bruninga at usna.edu
Thu Oct 12 18:08:52 UTC 2017
Be very careful about "Doppler correction" for digital modes.
>Falconsat just went over
>435.111 MHz to 435.095 MHz doppler corrected using MacDoppler...
Digital modes usually cannot stand the phase shift that occurs every time a
radio steps in frequency. Those bits are lost. If you set to 100 Hz
steps, over the full 18 kHz of Doppler, then 180 times during the pass, you
are *destroying* the data you are trying to decode.
So it is better to maybe step every 1 KHz and only have 18 blackouts instead
Assuming the decoder can still work with up to 500 Hz offset.
Doppler stepping is very helpful for SSB voice modes. But disasterous for
digital. That is for step tuned radios anyway.... I assume smart Doppler
correction in DSP receivers work around this problem?
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