WSJT-X/lib/fsk4hf/genfsk4.f90

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subroutine genfsk4(id,f00,nts,c)
parameter (ND=60) !Data symbols: LDPC (120,60), r=1/2
parameter (NN=ND) !Total symbols (60)
parameter (NSPS=57600) !Samples per symbol at 12000 sps
parameter (NZ=NSPS*NN) !Samples in waveform (3456000)
parameter (NFFT=NZ) !Full length FFT
complex c(0:NFFT-1) !Complex waveform
real*8 twopi,dt,fs,baud,f0,dphi,phi
integer id(NN) !Encoded 2-bit data (values 0-3)
f0=f00
twopi=8.d0*atan(1.d0)
fs=12000.d0
dt=1.0/fs
baud=1.d0/(NSPS*dt)
! Generate the 4-FSK waveform
x=0.
c=0.
phi=0.d0
k=-1
do j=1,NN
dphi=twopi*(f0 + nts*id(j)*baud)*dt
do i=1,NSPS
k=k+1
phi=phi+dphi
if(phi.gt.twopi) phi=phi-twopi
xphi=phi
c(k)=cmplx(cos(xphi),sin(xphi))
enddo
enddo
return
end subroutine genfsk4