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68 lines
2.4 KiB
Fortran
68 lines
2.4 KiB
Fortran
subroutine getcand2(ss,savg0,nts_q65,nagain,ntol,f0_selected,cand,ncand)
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! Get candidates for Q65 decodes, based on presence of sync tone.
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type candidate
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real :: snr !Relative S/N of sync detection
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real :: f !Freq of sync tone, 0 to 96000 Hz
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real :: xdt !DT of matching sync pattern, -1.0 to +4.0 s
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end type candidate
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parameter (NFFT=32768) !FFTs done in symspec()
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parameter (MAX_CANDIDATES=50)
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type(candidate) :: cand(MAX_CANDIDATES)
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real ss(322,NFFT) !Symbol spectra
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real savg0(NFFT),savg(NFFT) !Average spectra over whole Rx sequence
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integer ipk1(1) !Peak index of local portion of spectrum
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logical sync_ok !True if sync pattern is present
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data nseg/16/,npct/40/
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savg=savg0 !Save the original spectrum
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nlen=NFFT/nseg
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do iseg=1,nseg !Normalize spectrum with nearby baseline
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ja=(iseg-1)*nlen + 1
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jb=ja + nlen - 1
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call pctile(savg(ja),nlen,npct,base)
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savg(ja:jb)=savg(ja:jb)/(1.015*base)
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savg0(ja:jb)=savg0(ja:jb)/(1.015*base)
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enddo
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df=96000.0/NFFT
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bw=65*nts_q65*1.666666667 !Bandwidth of Q65 signal
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nbw=bw/df + 1 !Bandwidth in bins
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nb0=2*nts_q65 !Range of peak search, in bins
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smin=1.4 !First threshold
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nguard=5 !Guard range in bins
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i1=1
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i2=NFFT-nbw-nguard
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if(nagain.eq.1) then
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i1=nint((1000.0*f0_selected-ntol)/df)
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i2=nint((1000.0*f0_selected+ntol)/df)
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endif
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j=0
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do i=i1,i2 !Look for local peaks in average spectrum
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if(savg(i).lt.smin) cycle
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spk=maxval(savg(i:i+nb0))
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ipk1=maxloc(savg(i:i+nb0))
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i0=ipk1(1) + i - 1 !Index of local peak in savg()
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fpk=0.001*i0*df !Frequency of peak (kHz)
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! Check to see if sync tone is present.
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call q65_sync(ss,i0,nts_q65,sync_ok,snr_sync,xdt)
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if(.not.sync_ok) cycle
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! Sync tone is present, we have a candidate for decoding
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j=j+1
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cand(j)%f=fpk
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cand(j)%xdt=xdt
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cand(j)%snr=snr_sync
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ia=min(i,i0-nguard)
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ib=i0+nbw+nguard
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savg(ia:ib)=0.
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if(j.ge.MAX_CANDIDATES) exit
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enddo
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ncand=j !Total number of candidates found
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return
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end subroutine getcand2
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