mirror of https://github.com/saitohirga/WSJT-X.git
47 lines
1.1 KiB
Fortran
47 lines
1.1 KiB
Fortran
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subroutine downsam9(c0,npts8,nsps8,nspsd,fpk,c2,nz2)
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!Downsample to nspsd samples per symbol, info centered at fpk
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parameter (NMAX=128*31500)
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complex c0(0:npts8-1)
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complex c1(0:NMAX-1)
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complex c2(0:4096-1)
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fac=1.e-4
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c1(0:npts8-1)=fac*c0 !Copy c0 into c1
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do i=1,npts8-1,2
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c1(i)=-c1(i)
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enddo
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c1(npts8:)=0. !Zero the rest of c1
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nfft1=128*nsps8 !Forward FFT length
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nh1=nfft1/2
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df1=1500.0/nfft1
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call four2a(c1,nfft1,1,-1,1) !Forward FFT
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! do i=0,nfft1-1
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! f=i*df1
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! pp=real(c1(i))**2 + aimag(c1(i))**2
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! write(50,3009) i,f,1.e-6*pp
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!3009 format(i8,f12.3,f12.3)
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! enddo
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ndown=nsps8/16 !Downsample factor
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nfft2=nfft1/ndown !Backward FFT length
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nh2=nfft2/2
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fshift=fpk-1500.0
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i0=nh1 + fshift/df1
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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)=c1(j)
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enddo
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call four2a(c2,nfft2,1,1,1) !Backward FFT
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nspsd=nsps8/ndown
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nz2=npts8/ndown
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return
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end subroutine downsam9
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