WSJT-X/map65/libm65/iqcal.f90

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subroutine iqcal(nn,c,nfft,gain,phase,zsum,ipk,reject)
complex c(0:nfft-1)
complex z,zsum,zave
if(nn.eq.0) then
zsum=0.
endif
nn=nn+1
smax=0.
ipk=1
do i=1,nfft-1 !Find strongest signal
s=real(c(i))**2 + aimag(c(i))**2
if(s.gt.smax) then
smax=s
ipk=i
endif
enddo
pimage=real(c(nfft-ipk))**2 + aimag(c(nfft-ipk))**2
p=smax + pimage
z=c(ipk)*c(nfft-ipk)/p !Synchronous detection of image
zsum=zsum+z
zave=zsum/nn
tmp=sqrt(1.0 - (2.0*real(zave))**2)
phase=asin(2.0*aimag(zave)/tmp) !Estimate phase
gain=tmp/(1.0-2.0*real(zave)) !Estimate gain
reject=10.0*log10(pimage/smax)
return
end subroutine iqcal