On 10/02/2021 15:06, Bill Somerville wrote:
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.
Hi Alan,
note that the generator matrix widths above are for hex digits and
contain some excess zeros 26*4=101+3 excess and 19*4=74+2 excess
respectively.
We should have a more formal and complete document ready shortly.
73
Bill
G4WJS.
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