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Add detailed comments to get_candidates_fst240.f90.

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Joe Taylor 2020-06-29 09:37:29 -04:00
parent 494481fa8a
commit 4fbed923ab
1 changed files with 33 additions and 30 deletions
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63
lib/fst240_decode.f90
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@ -244,6 +244,7 @@ contains
endif
enddo
ncand=ic
xsnr=0.
do icand=1,ncand
sync=candidates(icand,2)
@ -351,8 +352,8 @@ contains
iaptype=0
qual=0.
fsig=fc_synced - 1.5*hmod*baud
write(21,'(i6,7i6,f7.1,f9.2,3f7.1,1x,a37)') &
nutc,icand,itry,iaptype,ijitter,ntype,nsync_qual,nharderrors,dmin,sync,xsnr,xdt,fsig,msg
!write(21,'(i6,7i6,f7.1,f9.2,3f7.1,1x,a37)') &
! nutc,icand,itry,iaptype,ijitter,ntype,nsync_qual,nharderrors,dmin,sync,xsnr,xdt,fsig,msg
call this%callback(nutc,smax1,nsnr,xdt,fsig,msg, &
iaptype,qual,ntrperiod)
goto 2002
@ -479,77 +480,79 @@ write(21,'(i6,7i6,f7.1,f9.2,3f7.1,1x,a37)') &
subroutine get_candidates_fst240(c_bigfft,nfft1,nsps,hmod,fs,fa,fb, &
ncand,candidates,base)
complex c_bigfft(0:nfft1/2)
integer hmod
integer indx(100),im(1)
real candidates(100,4)
real candidates0(100,4)
real snr_cand(100)
real s(18000)
real s2(18000)
real xdb(-3:3)
complex c_bigfft(0:nfft1/2) !Full length FFT of raw data
integer hmod !Modulation index (submode)
integer im(1) !For maxloc
real candidates(100,4) !Candidate list
real s(18000) !Low resolution power spectrum
real s2(18000) !CCF of s() with 4 tones
real xdb(-3:3) !Model 4-tone CCF peaks
data xdb/0.25,0.50,0.75,1.0,0.75,0.50,0.25/
data nfft1z/-1/
save nfft1z
nh1=nfft1/2
df1=fs/nfft1
baud=fs/nsps
baud=fs/nsps !Keying rate
df2=baud/2.0
nd=df2/df1
nd=df2/df1 !s() sums this many bins of big FFT
ndh=nd/2
ia=nint(max(100.0,fa)/df2)
ib=nint(min(4800.0,fb)/df2)
ia=nint(max(100.0,fa)/df2) !Low frequency search limit
ib=nint(min(4800.0,fb)/df2) !High frequency limit
signal_bw=4*(12000.0/nsps)*hmod
analysis_bw=min(4800.0,fb)-max(100.0,fa)
noise_bw=10.0*signal_bw
noise_bw=10.0*signal_bw !Is this a good compromise?
if(analysis_bw.gt.noise_bw) then
ina=ia
inb=ib
else
fcenter=(fa+fb)/2.0
fl = max(100.0,fcenter-noise_bw/2.)/df2
fcenter=(fa+fb)/2.0 !If noise_bw > analysis_bw,
fl = max(100.0,fcenter-noise_bw/2.)/df2 !we'll search over noise_bw
fh = min(4800.0,fcenter+noise_bw/2.)/df2
ina=nint(fl)
inb=nint(fh)
endif
s=0.
s=0. !Compute low-resloution power spectrum
do i=ina,inb ! noise analysis window includes signal analysis window
j0=nint(i*df2/df1)
do j=j0-ndh,j0+ndh
s(i)=s(i) + real(c_bigfft(j))**2 + aimag(c_bigfft(j))**2
enddo
enddo
ina=max(ina,1+3*hmod)
ina=max(ina,1+3*hmod) !Don't run off the ends
inb=min(inb,18000-3*hmod)
s2=0.
do i=ina,inb
do i=ina,inb !Compute CCF of s() and 4 tones
s2(i)=s(i-hmod*3) + s(i-hmod) +s(i+hmod) +s(i+hmod*3)
enddo
call pctile(s2(ina+hmod*3:inb-hmod*3),inb-ina+1-hmod*6,30,base)
s2=s2/base
thresh=1.25
s2=s2/base !Normalize wrt noise level
thresh=1.25 !First candidate threshold
ncand=0
candidates=0
if(ia.lt.3) ia=3
if(ib.gt.18000-2) ib=18000-2
! Find candidates, using the CLEAN algorithm to remove a model of each one
! from s2() after it has been found.
pval=99.99
do while(ncand.lt.100 .and. pval.gt.thresh)
im=maxloc(s2(ia:ib))
iploc=ia+im(1)-1
pval=s2(iploc)
if(s2(iploc).gt.thresh) then
do i=-3,+3
k=iploc+2*hmod*i
iploc=ia+im(1)-1 !Index of CCF peak
pval=s2(iploc) !Peak value
if(s2(iploc).gt.thresh) then !Is this a possible candidate?
do i=-3,+3 !Remove 0.9 of a model CCF at
k=iploc+2*hmod*i !this frequency from s2()
if(k.ge.ia .and. k.le.ib) then
s2(k)=max(0.,s2(k)-0.9*pval*xdb(i))
endif
enddo
ncand=ncand+1
candidates(ncand,1)=df2*iploc
candidates(ncand,2)=pval
candidates(ncand,1)=df2*iploc !Candidate frequency
candidates(ncand,2)=pval !Rough estimate of SNR
endif
enddo