mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-09-17 10:46:33 -04:00
a9623703b3
changes on the C++ side. Basically works except that Tx audio has incorrect DT and audio is truncated at the end. Also, command line decoding using JT9 is not as sensitive as decoding from within WSJT-X.
52 lines
1.3 KiB
Fortran
52 lines
1.3 KiB
Fortran
subroutine ft4_downsample(dd,newdata,f0,c)
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! Input: real data in dd() at sample rate 12000 Hz
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! Output: Complex data in c(), sampled at 1200 Hz
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include 'ft4_params.f90'
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parameter (NFFT2=NMAX/NDOWN)
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real dd(NMAX)
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complex c(0:NMAX/NDOWN-1)
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complex c1(0:NFFT2-1)
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complex cx(0:NMAX/2)
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real x(NMAX), window(0:NFFT2-1)
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equivalence (x,cx)
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logical first, newdata
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data first/.true./
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save first,window,x
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df=12000.0/NMAX
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baud=12000.0/NSPS
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if(first) then
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bw_transition = 0.5*baud
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bw_flat = 4*baud
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iwt = bw_transition / df
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iwf = bw_flat / df
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pi=4.0*atan(1.0)
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window(0:iwt-1) = 0.5*(1+cos(pi*(/(i,i=iwt-1,0,-1)/)/iwt))
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window(iwt:iwt+iwf-1)=1.0
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window(iwt+iwf:2*iwt+iwf-1) = 0.5*(1+cos(pi*(/(i,i=0,iwt-1)/)/iwt))
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window(2*iwt+iwf:)=0.0
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iws = baud / df
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window=cshift(window,iws)
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first=.false.
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endif
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if(newdata) then
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x=dd
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call four2a(x,NMAX,1,-1,0) !r2c FFT to freq domain
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endif
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i0=nint(f0/df)
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c1=0.
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if(i0.ge.0 .and. i0.le.NMAX/2) c1(0)=cx(i0)
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do i=1,NFFT2/2
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if(i0+i.le.NMAX/2) c1(i)=cx(i0+i)
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if(i0-i.ge.0) c1(NFFT2-i)=cx(i0-i)
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enddo
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c1=c1*window/NFFT2
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call four2a(c1,NFFT2,1,1,1) !c2c FFT back to time domain
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c=c1(0:NMAX/NDOWN-1)
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return
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end subroutine ft4_downsample
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