mirror of https://github.com/pavel-demin/ft8d.git
66 lines
1.5 KiB
Fortran
66 lines
1.5 KiB
Fortran
subroutine subtractft8(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 (NMAX=15*4000,NFRAME=640*79)
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parameter (NFFT=NMAX,NFILT=1400)
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real*4 window(-NFILT/2:NFILT/2),xjunk
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complex dd(NMAX)
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complex cref,camp,cfilt,cw
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integer itone(79)
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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),xjunk(NFRAME)
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save first
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if(f0.lt.2000.0) then
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f=f0+2000.0
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else
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f=f0-2000.0
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endif
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nstart=dt*4000+1
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call gen_ft8wave(itone,79,640,2.0,4000.0,f,cref,xjunk,1,NFRAME)
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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(first) then
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! Create and normalize the filter
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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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cw(1:NFILT+1)=window/sum
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cw=cshift(cw,NFILT/2+1)
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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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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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! 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)-cfilt(i)*cref(i)
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enddo
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return
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end subroutine subtractft8
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