On 17/07/2019 09:09, Conrad PA5Y wrote:
Hello Joe I am quite interested to learn more about the GMSK waveform
generation, where can I read more about it and the implementation in
WSJT-X and the advantages.
I will try to install the new release this evening.
Many thanks
Conrad PA5Y
Hi Conrad,
I believe Steve, K9AN, is writing up a short paper on the FT8 and FT4
modulation details aimed particularly at 3rd party implementers who wish
to generate equivalent waveforms. GMSK is a modification of the MSK
waveform by smoothing the frequency shifts, in WSJT-X we generate the
whole message waveform in advance rather than the instantaneous
calculations we use for MFSK signals to generate the phase angle and
hence the instantaneous value of each sample.
If you have the skills then the implementations are here:
https://sourceforge.net/p/wsjt/wsjtx/ci/master/tree/lib/ft8/gen_ft8wave.f90
and here:
https://sourceforge.net/p/wsjt/wsjtx/ci/master/tree/lib/ft4/gen_ft4wave.f90
Note that the FT4 waveform includes a start and end padding to allow for
ramp up and down and to accommodate the overhang from the Gaussian
smoothing, the final FT8 waveform does not include this padding as it
has to remain compatible with the old MFSK FT8 waveform.
73
Bill
G4WJS.
_______________________________________________
wsjt-devel mailing list
wsjt-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/wsjt-devel
