WSJT-X/lib/ft4/ft4_params.f90

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! FT4
! LDPC(174,91) code, four 4x4 Costas arrays for sync, ramp-up and ramp-down symbols
parameter (KK=91) !Information bits (77 + CRC14)
parameter (ND=87) !Data symbols
parameter (NS=16) !Sync symbols
parameter (NN=NS+ND) !Sync and data symbols (103)
parameter (NN2=NS+ND+2) !Total channel symbols (105)
parameter (NSPS=576) !Samples per symbol at 12000 S/s
parameter (NZ=NSPS*NN) !Sync and Data samples (59328)
parameter (NZ2=NSPS*NN2) !Total samples in shaped waveform (60480)
parameter (NMAX=21*3456) !Samples in iwave (72576)
parameter (NFFT1=2304, NH1=NFFT1/2) !Length of FFTs for symbol spectra
parameter (NSTEP=NSPS) !Coarse time-sync step size
parameter (NHSYM=(NMAX-NFFT1)/NSTEP) !Number of symbol spectra (1/4-sym steps)
parameter (NDOWN=18) !Downsample factor