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102 lines
2.1 KiB
Fortran
102 lines
2.1 KiB
Fortran
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subroutine qpc_sync(crcvd0,fsample,isync,fsync,ftol,f2,t2,snrsync)
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parameter(N9SEC=9*12000,NMAX=15*12000,NDOWN=16,NZ=N9SEC/NDOWN)
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complex crcvd0(NMAX) !Signal as received
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complex c0(0:N9SEC-1) !For long FFT
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complex c1(0:NZ-1)
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complex c1sum(0:NZ-1)
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complex z
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real s(N9SEC/4)
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real p(-1125:1125)
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integer ipk(1)
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integer isync(24)
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baud=12000.0/1024.0
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df2=fsample/N9SEC
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fac=1.0/N9SEC
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c0=fac*crcvd0(1:N9SEC)
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call four2a(c0,N9SEC,1,-1,1) !Forward c2c FFT
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iz=N9SEC/4
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do i=1,iz
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s(i)=real(c0(i))**2 + aimag(c0(i))**2
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enddo
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do i=1,4 !Smooth the spectrum a bit
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call smo121(s,iz)
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enddo
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ia=nint((fsync-ftol)/df2)
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ib=nint((fsync+ftol)/df2)
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ipk=maxloc(s(ia:ib))
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i0=ipk(1) + ia - 1
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f2=df2*i0-750.0 ! f2 is the offset from nominal 750 Hz.
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ia=nint(i0-baud/df2)
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ib=nint(i0+baud/df2)
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s1=0.0
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s0=0.0
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do i=ia,ib
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s0=s0+s(i)
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s1=s1+(i-i0)*s(i)
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enddo
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delta=s1/s0
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i0=nint(i0+delta)
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f2=i0*df2-750.0
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c1=0.
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ia=nint(i0-baud/df2)
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ib=nint(i0+baud/df2)
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do i=ia,ib
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j=i-i0
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if(j.ge.0) c1(j)=c0(i)
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if(j.lt.0) c1(j+NZ)=c0(i)
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enddo
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call four2a(c1,NZ,1,1,1) !Reverse c2c FFT: back to time domain
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c1sum(0)=c1(0)
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do i=1,NZ-1
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c1sum(i)=c1sum(i-1) + c1(i)
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enddo
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nspsd=1024/NDOWN
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dt=NDOWN/12000.0
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lagmax=1.5/dt
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i0=nint(0.5*fsample/NDOWN) !Nominal start time is 0.5 s
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pmax=0.
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lagpk=0
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do lag=-lagmax,lagmax
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sp=0.
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do j=1,24
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i1=i0 + (isync(j)-1)*nspsd + lag
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i2=i1 + nspsd
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if(i1.lt.0 .or. i1.gt.NZ-1) cycle
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if(i2.lt.0 .or. i2.gt.NZ-1) cycle
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z=c1sum(i2)-c1sum(i1)
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sp=sp + real(z)**2 + aimag(z)**2
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enddo
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if(sp.gt.pmax) then
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pmax=sp
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lagpk=lag
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endif
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p(lag)=sp
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enddo
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t2=lagpk*dt
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snrsync=0.
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sp=0.
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sq=0.
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nsum=0
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tsym=1024/12000.0
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do lag=-lagmax,lagmax
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t=(lag-lagpk)*dt
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if(abs(t).lt.tsym) cycle
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nsum=nsum+1
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sp=sp + p(lag)
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sq=sq + p(lag)*p(lag)
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enddo
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ave=sp/nsum
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rms=sqrt(sq/nsum-ave*ave)
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snrsync=(pmax-ave)/rms
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return
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end subroutine qpc_sync
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