WSJT-X/lib/ft4/getcandidates4.f90

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subroutine getcandidates4(dd,fa,fb,syncmin,nfqso,maxcand,savg,candidate, &
ncand,sbase)
include 'ft4_params.f90'
real s(NH1,NHSYM)
real savg(NH1),savsm(NH1)
real sbase(NH1)
real x(NFFT1)
real window(NFFT1)
complex cx(0:NH1)
real candidate(2,maxcand),candidatet(2,maxcand)
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real dd(NMAX)
equivalence (x,cx)
logical first
data first/.true./
save first,window
if(first) then
first=.false.
pi=4.0*atan(1.)
window=0.
call nuttal_window(window,NFFT1)
endif
! Compute symbol spectra, stepping by NSTEP steps.
savg=0.
df=12000.0/NFFT1
fac=1.0/300.0
do j=1,NHSYM
ia=(j-1)*NSTEP + 1
ib=ia+NFFT1-1
if(ib.gt.NMAX) exit
x=fac*dd(ia:ib)*window
call four2a(x,NFFT1,1,-1,0) !r2c FFT
s(1:NH1,j)=abs(cx(1:NH1))**2
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savg=savg + s(1:NH1,j) !Average spectrum
enddo
savg=savg/NHSYM
savsm=0.
do i=8,NH1-7
savsm(i)=sum(savg(i-7:i+7))/15.
enddo
nfa=fa/df
if(nfa.lt.nint(200.0/df)) nfa=nint(200.0/df)
nfb=fb/df
if(nfb.gt.nint(4910.0/df)) nfb=nint(4910.0/df)
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call ft4_baseline(savg,nfa,nfb,sbase)
if(any(sbase(nfa:nfb).le.0)) return
savsm(nfa:nfb)=savsm(nfa:nfb)/sbase(nfa:nfb)
f_offset = -1.5*12000.0/NSPS
ncand=0
candidatet=0
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do i=nfa+1,nfb-1
if(savsm(i).ge.savsm(i-1) .and. savsm(i).ge.savsm(i+1) .and. &
savsm(i).ge.syncmin) then
den=savsm(i-1)-2*savsm(i)+savsm(i+1)
del=0.
if(den.ne.0.0) del=0.5*(savsm(i-1)-savsm(i+1))/den
fpeak=(i+del)*df+f_offset
if(fpeak.lt.200.0 .or. fpeak.gt.4910.0) cycle
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speak=savsm(i) - 0.25*(savsm(i-1)-savsm(i+1))*del
ncand=ncand+1
candidatet(1,ncand)=fpeak
candidatet(2,ncand)=speak
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if(ncand.eq.maxcand) exit
endif
enddo
candidate=0
nq=count(abs(candidatet(1,1:ncand)-nfqso).le.20.0)
n1=1
n2=nq+1
do i=1,ncand
if(abs(candidatet(1,i)-nfqso).le.20.0) then
candidate(1:2,n1)=candidatet(1:2,i)
n1=n1+1
else
candidate(1:2,n2)=candidatet(1:2,i)
n2=n2+1
endif
enddo
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return
end subroutine getcandidates4