mirror of
https://github.com/saitohirga/WSJT-X.git
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113 lines
2.6 KiB
FortranFixed
113 lines
2.6 KiB
FortranFixed
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subroutine syncf1(data,jz,jstart,f0,NFreeze,smax,red)
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C Does 16k FFTs of data with stepsize 15360, using only "sync on" intervals.
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C Returns a refined value of f0, the sync-tone frequency.
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parameter (NFFT=16384)
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parameter (NH=NFFT/2)
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parameter (NQ=NFFT/4)
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parameter (NB3=3*512)
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real data(jz) !Raw data
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real x(NFFT)
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real red(512)
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real s(NQ) !Ref spectrum for flattening and birdie-zapping
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complex c(0:NH)
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complex z
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equivalence (x,c)
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ps(z)=real(z)**2 + imag(z)**2 !Power spectrum ASF
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C Accumulate a high-resolution average spectrum
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df=11025.0/NFFT
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jstep=10*NB3
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nz=(jz-jstart)/jstep -1
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call zero(s,NQ)
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do n=1,nz
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call zero(x,NFFT)
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k=(n-1)*jstep
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do i=1,10
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j=(i-1)*NB3 + 1
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call move(data(jstart+k+j),x(j),512)
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enddo
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call xfft(x,NFFT)
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do i=1,NQ
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x(i)=ps(c(i))
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enddo
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call add(s,x,s,NQ)
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enddo
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fac=(1.0/NFFT)**2
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do i=1,NQ !Normalize
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s(i)=fac*s(i)
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enddo
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C NB: could also compute a "blue" spectrum, using the sync-off intervals.
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n8=NQ/8
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do i=1,n8
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red(i)=0.
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do k=8*i-7,8*i
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red(i)=red(i)+s(k)
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enddo
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red(i)=10.0*red(i)/(8.0*nz)
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enddo
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C Find improved value for f0
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smax=0.
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ia=(f0-25.)/df
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ib=(f0+25.)/df
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if(NFreeze.eq.1) then
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ia=(f0-5.)/df
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ib=(f0+5.)/df
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endif
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do i=ia,ib
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if(s(i).gt.smax) then
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smax=s(i)
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ipk=i
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endif
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enddo
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f0=ipk*df
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C Remove line at f0 from spectrum -- if it's strong enough.
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ia=(f0-150)/df
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ib=(f0+150)/df
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a1=0.
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a2=0.
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nsum=50
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do i=1,nsum
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a1=a1+s(ia-i)
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a2=a2+s(ib+i)
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enddo
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a1=a1/nsum
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a2=a2/nsum
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smax=2.0*smax/(a1+a2)
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if(smax.gt.3.0) then
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b=(a2-a1)/(ib-ia)
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do i=ia,ib
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s(i)=a1 + (i-ia)*b
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enddo
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endif
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C Make a smoothed version of the spectrum.
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nsum=50
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fac=1./(2*nsum+1)
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call zero(x,nsum)
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call zero(s,50)
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call zero(s(NQ-nsum),nsum)
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sum=0.
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do i=nsum+1,NQ-nsum
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sum=sum+s(i+nsum)-s(i-nsum)
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x(i)=fac*sum
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enddo
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call zero(x(NQ-nsum),nsum+1)
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C To zap birdies, compare s(i) and x(i). If s(i) is larger by more
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C than some limit, replace x(i) by s(i). That will put narrow birdies
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C on top of the smoothed spectrum.
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call move(x,s,NQ) !Copy smoothed spectrum into s
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return
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end
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