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https://github.com/saitohirga/WSJT-X.git
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64 lines
1.7 KiB
Fortran
64 lines
1.7 KiB
Fortran
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subroutine genfsk4(id,f0,c)
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parameter (NR=4) !Ramp up, ramp down
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parameter (NS=12) !Sync symbols (2 @ Costas 4x4)
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parameter (ND=84) !Data symbols: LDPC (168,84), r=1/2
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parameter (NN=NR+NS+ND) !Total symbols (100)
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parameter (NSPS=2688) !Samples per symbol at 12000 sps
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parameter (NZ=NSPS*NN) !Samples in waveform (268800)
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parameter (NFFT=512*1024)
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parameter (NSYNC=NS*NSPS)
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parameter (NDOWN=168)
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parameter (NFFT2=NZ/NDOWN,NH2=NFFT2/2) !3200
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parameter (NSPSD=NFFT2/NN)
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complex c(0:NFFT-1) !Complex waveform
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complex cf(0:NFFT-1)
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real*8 twopi,dt,fs,baud,f0,dphi,phi
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integer id(NN) !Encoded 2-bit data (values 0-3)
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integer icos4(4) !4x4 Costas array
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data icos4/0,1,3,2/
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twopi=8.d0*atan(1.d0)
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fs=12000.d0
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dt=1.0/fs
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baud=1.d0/(NSPS*dt)
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! Generate the 4-FSK waveform
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x=0.
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c=0.
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phi=0.d0
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k=-1
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do j=1,NN
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dphi=twopi*(f0 + id(j)*baud)*dt
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do i=1,NSPS
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k=k+1
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phi=phi+dphi
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if(phi.gt.twopi) phi=phi-twopi
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xphi=phi
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c(k)=cmplx(cos(xphi),sin(xphi))
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enddo
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enddo
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nh=NFFT/2
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df=12000.0/NFFT
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cf=c
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call four2a(cf,NFFT,1,-1,1) !Transform to frequency domain
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if(sum(id).ne.0) then
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flo=f0-baud
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fhi=f0+4*baud
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do i=0,NFFT-1 !Remove spectral sidelobes
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f=i*df
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if(i.gt.nh) f=(i-nfft)*df
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if(f.le.flo .or. f.ge.fhi) cf(i)=0.
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enddo
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endif
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c=cf
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call four2a(c,NFFT,1,1,1) !Transform back to time domain
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c=c/nfft
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return
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end subroutine genfsk4
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