On 10/02/2021 14:40, Alan Hopper wrote:
Hi,
I'm trying to write a FST4 encoder without using the source, I'm most
of the way there using the excellent FT4_FT8_QEX and FST4_Quick_Start
docs, the latter mentions generator_fst4.dat and
generator_fst4w.dat which I can't find. Are these available or can I
extract those tables from the source without breaching the licence?
Also what BT is used for the Gaussian shaping. I see details of the 50
bit payload are 'in preparation', If you want a proofreader, I'll very
happily proof read by trying to implement it:)
Thanks again for the great documentation and modes.
73 Alan M0NNB
Hi Alan,
I though there was a document describing the FST4 and FST4W protocols,
but I can find it right now. Yes you can use the parity generators as
they are part of the protocol.
Here's the FST4 LDPC generator, a 139 by 26 matrix generating 139 parity
bits from 101 (77 + 24 bits CRC) message bits:
https://sourceforge.net/p/wsjt/wsjtx/ci/master/tree/lib/fst4/ldpc_240_101_generator.f90
and here's the FST4W LDPC generator, a 166 by 19 matrix generating 166
parity bits from 74 (50 + 24 bits CRC) message bits:
https://sourceforge.net/p/wsjt/wsjtx/ci/master/tree/lib/fst4/ldpc_240_74_generator.f90
you will have to take my word for these two specific files being in the
public domain for now.
BT for the WSJT-X FST4 and FST4W waveform Gaussian frequency smoothing
is 2.0.
73
Bill
G4WJS.
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