subroutine subtractft8(dd0,itone,f0,dt,lrefinedt) ! Subtract an ft8 signal ! ! Measured signal : dd(t) = a(t)cos(2*pi*f0*t+theta(t)) ! Reference signal : cref(t) = exp( j*(2*pi*f0*t+phi(t)) ) ! Complex amp : cfilt(t) = LPF[ dd(t)*CONJG(cref(t)) ] ! Subtract : dd(t) = dd(t) - 2*REAL{cref*cfilt} parameter (NMAX=15*12000,NFRAME=1920*79) parameter (NFFT=NMAX,NFILT=4000) real dd(NMAX),dd0(NMAX) real window(-NFILT/2:NFILT/2) real x(NFFT+2) real endcorrection(NFILT/2+1) complex cx(0:NFFT/2) complex cref,camp,cfilt,cw,z integer itone(79) logical first,lrefinedt,ldt data first/.true./ common/heap8/cref(NFRAME),camp(NMAX),cfilt(NMAX),cw(NMAX) equivalence (x,cx) save first,/heap8/,endcorrection if(first) then ! Create and normalize the filter pi=4.0*atan(1.0) fac=1.0/float(nfft) sumw=0.0 do j=-NFILT/2,NFILT/2 window(j)=cos(pi*j/NFILT)**2 sumw=sumw+window(j) enddo cw=0. cw(1:NFILT+1)=window/sumw cw=cshift(cw,NFILT/2+1) call four2a(cw,nfft,1,-1,1) cw=cw*fac first=.false. do j=1,NFILT/2+1 endcorrection(j)=1.0/(1.0-sum(window(j-1:NFILT/2))/sumw) enddo endif ! Generate complex reference waveform cref call gen_ft8wave(itone,79,1920,2.0,12000.0,f0,cref,xjunk,1,NFRAME) ldt=lrefinedt if(ldt) then !Are we refining DT ? sqa=sqf(-90) sqb=sqf(+90) sq0=sqf(0) call peakup(sqa,sq0,sqb,dx) if(abs(dx).gt.1.0) return !No acceptable minimum: do not subtract i2=nint(90.0*dx) !Best estimate of idt ldt=.false. sq0=sqf(i2) !Do the subtraction with idt=i2 else sq0=sqf(0) !Do the subtraction with idt=0 endif dd0=dd !Return dd0 with this signal subtracted return contains real function sqf(idt) !Internal function: all variables accessible nstart=dt*12000+1 + idt camp=0. dd=dd0 do i=1,nframe j=nstart-1+i if(j.ge.1.and.j.le.NMAX) camp(i)=dd(j)*conjg(cref(i)) enddo cfilt(1:nframe)=camp(1:nframe) cfilt(nframe+1:)=0.0 call four2a(cfilt,nfft,1,-1,1) cfilt(1:nfft)=cfilt(1:nfft)*cw(1:nfft) call four2a(cfilt,nfft,1,1,1) cfilt(1:NFILT/2+1)=cfilt(1:NFILT/2+1)*endcorrection cfilt(nframe:nframe-NFILT/2:-1)=cfilt(nframe:nframe-NFILT/2:-1)*endcorrection x=0. do i=1,nframe j=nstart+i-1 if(j.ge.1 .and. j.le.NMAX) then z=cfilt(i)*cref(i) dd(j)=dd(j)-2.0*real(z) !Subtract the reconstructed signal x(i)=dd(j) endif enddo sqq=0. if(ldt) then call four2a(cx,NFFT,1,-1,0) !Forward FFT, r2c df=12000.0/NFFT ia=(f0-1.5*6.25)/df ib=(f0+8.5*6.25)/df do i=ia,ib sqq=sqq + real(cx(i))*real(cx(i)) + aimag(cx(i))*aimag(cx(i)) enddo endif sqf=sqq return end function sqf end subroutine subtractft8