mirror of https://github.com/saitohirga/WSJT-X.git
61 lines
1.5 KiB
Fortran
61 lines
1.5 KiB
Fortran
subroutine downsam9(id2,npts8,nsps8,newdat,nspsd,fpk,c2,nz2)
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!Downsample from id2() into C2() so as to yield nspsd samples per symbol,
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!mixing from fpk down to zero frequency.
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include 'constants.f90'
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parameter (NMAX1=1024*1920)
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integer*2 id2(0:8*npts8-1)
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real*4 x1(0:NMAX1-1)
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complex c1(0:NMAX1/2)
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complex c2(0:4096-1)
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real s(5000)
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equivalence (c1,x1)
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save
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nfft1=1024*nsps8 !Forward FFT length
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df1=12000.0/nfft1
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npts=8*npts8
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if(newdat.eq.1) then
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fac=6.963e-6 !Why this weird constant?
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do i=0,npts-1
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x1(i)=fac*id2(i)
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enddo
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x1(npts:nfft1-1)=0. !Zero the rest of x1
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call four2a(c1,nfft1,1,-1,0) !Forward FFT, r2c
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nadd=1.0/df1
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s=0.
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do i=1,5000
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j=(i-1)/df1
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do n=1,nadd
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j=j+1
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s(i)=s(i)+real(c1(j))**2 + aimag(c1(j))**2
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enddo
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enddo
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endif
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ndown=8*nsps8/nspsd !Downsample factor
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nfft2=nfft1/ndown !Backward FFT length
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nh2=nfft2/2
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nf=nint(fpk)
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i0=fpk/df1
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nw=100
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ia=max(1,nf-nw)
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ib=min(5000,nf+nw)
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call pctile(s(ia),ib-ia+1,40,avenoise)
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fac=sqrt(1.0/avenoise)
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do i=0,nfft2-1
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j=i0+i
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if(i.gt.nh2) j=j-nfft2
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c2(i)=fac*c1(j)
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enddo
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call four2a(c2,nfft2,1,1,1) !FFT back to time domain
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nz2=8*npts8/ndown
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return
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end subroutine downsam9
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