WSJT-X/lib/spec64.f90

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subroutine spec64(c0,npts2,mode64,jpk,s3,LL,NN)
parameter (NSPS=3456) !Samples per symbol at 6000 Hz
complex c0(0:360000) !Complex spectrum of dd()
complex cs(0:NSPS-1) !Complex symbol spectrum
real s3(LL,NN) !Synchronized symbol spectra
real xbase0(LL),xbase(LL)
nfft=nsps
fac=1.0/nfft
do j=1,NN
jj=j+7 !Skip first Costas array
if(j.ge.33) jj=j+14 !Skip middle Costas array
ja=jpk + (jj-1)*nfft
jb=ja+nfft-1
cs(0:nfft-1)=fac*c0(ja:jb)
call four2a(cs,nfft,1,-1,1)
do ii=1,LL
i=ii-65
if(i.lt.0) i=i+nfft
s3(ii,j)=real(cs(i))**2 + aimag(cs(i))**2
enddo
enddo
df=6000.0/nfft
do i=1,LL
call pctile(s3(i,1:NN),NN,45,xbase0(i)) !Get baseline for passband shape
enddo
nh=25
xbase(1:nh-1)=sum(xbase0(1:nh-1))/(nh-1.0)
xbase(LL-nh+1:LL)=sum(xbase0(LL-nh+1:LL))/(nh-1.0)
do i=nh,LL-nh
xbase(i)=sum(xbase0(i-nh+1:i+nh))/(2*nh+1) !Smoothed passband shape
enddo
do i=1,LL
s3(i,1:NN)=s3(i,1:NN)/(xbase(i)+0.001) !Apply frequency equalization
enddo
return
end subroutine spec64