97 lines
2.4 KiB
Fortran
97 lines
2.4 KiB
Fortran
subroutine subtractjs8(dd,itone,f0,dt)
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! Subtract an ft8 signal
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!
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! Measured signal : dd(t) = a(t)cos(2*pi*f0*t+theta(t))
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! Reference signal : cref(t) = exp( j*(2*pi*f0*t+phi(t)) )
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! Complex amp : cfilt(t) = LPF[ dd(t)*CONJG(cref(t)) ]
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! Subtract : dd(t) = dd(t) - 2*REAL{cref*cfilt}
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parameter (NFRAME=NSPS*NN)
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parameter (NFFT=NMAX, NFILT=1400)
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real dd(NMAX), window(-NFILT/2:NFILT/2)
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complex cref,camp,cfilt,cw
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integer itone(NN)
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logical first
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data first/.true./
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common/heap8/cref(NFRAME),camp(NMAX),cfilt(NMAX),cw(NMAX)
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save first
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nstart=dt*12000+1
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if(NWRITELOG.eq.1) then
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write(*,*) '<DecodeDebug> generating reference signal', nstart
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flush(6)
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endif
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call genjs8refsig(itone,cref,f0)
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camp=0.
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do i=1,NFRAME
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id=nstart-1+i
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if(id.ge.1.and.id.le.NMAX) camp(i)=dd(id)*conjg(cref(i))
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enddo
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if(NWRITELOG.eq.1) then
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write(*,*) '<DecodeDebug> filtering', NFFT
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flush(6)
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endif
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if(first) then
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! Create and normalize the filter
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if(NWRITELOG.eq.1) then
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write(*,*) '<DecodeDebug> creating and normalizing filter'
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flush(6)
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endif
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pi=4.0*atan(1.0)
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fac=1.0/float(NFFT)
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sum=0.0
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do j=-NFILT/2,NFILT/2
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window(j)=cos(pi*j/NFILT)**2
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sum=sum+window(j)
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enddo
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cw=0.
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! this ultimately shifts 1/2 of the window out of computation
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! since it's multiplied against cfilt whiich will only have amp
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! values for NFRAME length, which will always be > 20000 samples
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! longer than the NFRAME.
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! cw(1:NFILT+1)=window/sum
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! cw=cshift(cw,NFILT/2+1)
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cw(1:NFILT/2)=window(1:NFILT/2)
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! we really don't even need the second half of the window.
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! start=NMAX-NFILT/2
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! end=NMAX-NFILT+1
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! cw(start:end)=window(-NFILT/2:1)
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cw=cw/sum
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call four2a(cw,NFFT,1,-1,1)
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cw=cw*fac
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first=.false.
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endif
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if(NWRITELOG.eq.1) then
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write(*,*) '<DecodeDebug> generating complex amplitude'
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flush(6)
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endif
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cfilt=0.0
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cfilt(1:NFRAME)=camp(1:NFRAME)
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call four2a(cfilt,NFFT,1,-1,1)
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cfilt(1:NFFT)=cfilt(1:NFFT)*cw(1:NFFT)
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call four2a(cfilt,NFFT,1,1,1)
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if(NWRITELOG.eq.1) then
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write(*,*) '<DecodeDebug> subtracting filtered reference', NFFT
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flush(6)
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endif
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! Subtract the reconstructed signal
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do i=1,NFRAME
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j=nstart+i-1
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if(j.ge.1 .and. j.le.NMAX) dd(j)=dd(j)-2*REAL(cfilt(i)*cref(i))
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enddo
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return
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end subroutine subtractjs8
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