WSJT-X/lib/ft8/subtractft8.f90
2020-02-26 13:14:49 -05:00

104 lines
3.0 KiB
Fortran

subroutine subtractft8(dd0,itone,f0,dt,ldt)
! 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=2800)
real dd(NMAX),dd0(NMAX)
real window(-NFILT/2:NFILT/2)
real x(NFFT+2)
complex cx(0:NFFT/2)
complex cref,camp,cfilt,cw,z
integer itone(79)
logical first,ldt
data first/.true./
common/heap8/cref(NFRAME),camp(NMAX),cfilt(NMAX),cw(NMAX)
equivalence (x,cx)
save first,/heap8/
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.
endif
! Generate complex reference waveform cref
call gen_ft8wave(itone,79,1920,2.0,12000.0,f0,cref,xjunk,1,NFRAME)
if(ldt) then !Are we refining DT ?
sqa=sqf(-300)
sqb=sqf(300)
sq0=sqf(0) !Do the subtraction with idt=0
call peakup(sqa,sq0,sqb,dx)
if(abs(dx).gt.1.0) return !No acceptable minimum: do not subtract
i1=nint(300.0*dx) !First approximation of best idt
sqa=sqf(i1-60)
sqb=sqf(i1+60)
sq0=sqf(i1)
call peakup(sqa,sq0,sqb,dx)
if(abs(dx).gt.1.0) return !No acceptable minimum: do not subtract
i2=nint(60.0*dx) + i1 !Best estimate of idt
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)
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