WSJT-X/lib/fsk4hf/spec4.f90

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subroutine spec4(c,s,savg)
parameter (KK=84) !Information bits (72 + CRC12)
parameter (ND=84) !Data symbols: LDPC (168,84), r=1/2
parameter (NS=12) !Sync symbols (3 @ 4x4 Costas arrays)
parameter (NR=2) !Ramp up/down
parameter (NN=NR+NS+ND) !Total symbols (98)
parameter (NSPS=2688/84) !Samples per symbol (32)
parameter (NZ=NSPS*NN) !Samples in baseband waveform (3760)
parameter (NFFT=2*NSPS,NH=NSPS)
complex c(0:NZ-1)
complex c1(0:NFFT-1)
real s(0:NH,NN)
real savg(0:NH)
fs=12000.0/84.0
df=fs/NFFT
savg=0.
do j=1,NN
ia=(j-1)*NSPS
ib=ia + NSPS-1
c1(0:NSPS-1)=c(ia:ib)
c1(NSPS:)=0.
call four2a(c1,NFFT,1,-1,1)
do k=1,NSPS
s(k,j)=real(c1(k))**2 + aimag(c1(k))**2
enddo
savg=savg+s(0:NH,j)
enddo
s=s/NZ
savg=savg/(NN*NZ)
return
end subroutine spec4