WSJT-X/lib/sync_q65.f90
2020-11-02 15:59:10 -05:00

135 lines
3.9 KiB
Fortran

subroutine sync_q65(iwave,nmax,mode65,nsps,nfqso,ntol,xdt,f0,snr1,width)
! Detect and align with the Q65 sync vector, returning time and frequency
! offsets and SNR estimate.
! Input: iwave(0:nmax-1) Raw data
! mode65 Tone spacing 1 2 4 8 16 (A-E)
! nsps Samples per symbol at 12000 Sa/s
! nfqso Target frequency (Hz)
! ntol Search range around nfqso (Hz)
! Output: xdt Time offset from nominal (s)
! f0 Frequency of sync tone
! snr1 Relative SNR of sync signal
parameter (NSTEP=8) !Step size nsps/NSTEP
integer*2 iwave(0:nmax-1) !Raw data
integer isync(22) !Indices of sync symbols
integer ijpk(2) !Indices i and j at peak of ccf
real, allocatable :: s1(:,:) !Symbol spectra, quarter-symbol steps
real sync(85) !sync vector
real ccf(-64:64,-53:214) !CCF(freq,time)
complex, allocatable :: c0(:) !Complex spectrum of symbol
data isync/1,9,12,13,15,22,23,26,27,33,35,38,46,50,55,60,62,66,69,74,76,85/
data sync(1)/99.0/
save sync
nfft=2*nsps
df=12000.0/nfft !Freq resolution = 0.5*baud
istep=nsps/NSTEP
iz=5000.0/df !Uppermost frequency bin, at 5000 Hz
txt=85.0*nsps/12000.0
jz=(txt+1.0)*12000.0/istep !Number of quarter-symbol steps
if(nsps.ge.6912) jz=(txt+2.0)*12000.0/istep !For TR 60 s and higher
allocate(s1(iz,jz))
allocate(c0(0:nfft-1))
if(sync(1).eq.99.0) then !Generate the sync vector
sync=-22.0/63.0 !Sync tone OFF
do k=1,22
sync(isync(k))=1.0 !Sync tone ON
enddo
endif
fac=1/32767.0
do j=1,jz !Compute symbol spectra at step size
ia=(j-1)*istep
ib=ia+nsps-1
k=-1
do i=ia,ib,2 !Load iwave data into complex array c0, for r2c FFT
xx=iwave(i)
yy=iwave(i+1)
k=k+1
c0(k)=fac*cmplx(xx,yy)
enddo
c0(k+1:)=0.
call four2a(c0,nfft,1,-1,0) !r2c FFT
do i=1,iz
s1(i,j)=real(c0(i))**2 + aimag(c0(i))**2
enddo
! For large Doppler spreads, should we smooth the spectra here?
call smo121(s1(1:iz,j),iz)
enddo
i0=nint(nfqso/df) !Target QSO frequency
call pctile(s1(i0-64:i0+192,1:jz),129*jz,40,base)
s1=s1/base - 1.0
! Apply fast AGC
s1max=20.0 !Empirical choice
do j=1,jz
smax=maxval(s1(i0-64:i0+192,j))
if(smax.gt.s1max) s1(i0-64:i0+192,j)=s1(i0-64:i0+192,j)*s1max/smax
enddo
dtstep=nsps/(NSTEP*12000.0) !Step size in seconds
ia=min(64,nint(ntol/df))
lag1=-1.0/dtstep
lag2=1.0/dtstep + 0.9999
j0=0.5/dtstep
if(nsps.ge.6192) then
j0=1.0/dtstep !Nominal index for start of signal
lag2=4.0/dtstep + 0.9999 !Include EME delays
endif
ccf=0.
do lag=lag1,lag2
do k=1,85
n=NSTEP*(k-1) + 1
j=n+lag+j0
if(j.ge.1 .and. j.le.jz) then
ccf(-ia:ia,lag)=ccf(-ia:ia,lag) + sync(k)*s1(i0-ia:i0+ia,j)
endif
enddo
enddo
ijpk=maxloc(ccf)
ipk=ijpk(1)-65
jpk=ijpk(2)-54
f0=nfqso + ipk*df
xdt=jpk*dtstep
sq=0.
nsq=0
do j=lag1,lag2
if(abs(j-jpk).gt.6) then
sq=sq + ccf(ipk,j)**2
nsq=nsq+1
endif
enddo
rms=sqrt(sq/nsq)
smax=ccf(ipk,jpk)
snr1=smax/rms
! do j=lag1,lag2
! write(55,3055) j,j*dtstep,ccf(ipk,j)/rms
!3055 format(i5,f8.3,f10.3)
! enddo
! do i=-ia,ia
! write(56,3056) i*df,ccf(i,jpk)/rms
!3056 format(2f10.3)
! enddo
! flush(56)
acf0=dot_product(ccf(-ia:ia,jpk),ccf(-ia:ia,jpk))
do i=1,ia
acf=dot_product(ccf(-ia:ia,jpk),ccf(-ia+i:ia+i,jpk))
if(acf.le.0.5*acf0) exit
enddo
width=i*1.414*df
return
end subroutine sync_q65