WSJT-X/lib/sync64.f90

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Fortran
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subroutine sync64(dd,nf1,nf2,nfqso,ntol,mode64,maxf1,dtx,f0,jpk,kpk,snrdb,c0)
parameter (NMAX=60*12000) !Max size of raw data at 12000 Hz
parameter (NSPS=2304) !Samples per symbol at 4000 Hz
parameter (NSPC=7*NSPS) !Samples per Costas array
real dd(NMAX) !Raw data
real s1(0:NSPC-1) !Power spectrum of Costas 1
real s2(0:NSPC-1) !Power spectrum of Costas 2
real s3(0:NSPC-1) !Power spectrum of Costas 3
real s0(0:NSPC-1) !Sum of s1+s2+s3
real s0a(0:NSPC-1) !Best synchromized spectrum (saved)
real s0b(0:NSPC-1) !tmp
real a(5)
integer icos7(0:6) !Costas 7x7 tones
integer ipk0(1)
complex cc(0:NSPC-1) !Costas waveform
complex c0(0:360000) !Complex spectrum of dd()
complex c1(0:NSPC-1) !Complex spectrum of Costas 1
complex c2(0:NSPC-1) !Complex spectrum of Costas 2
complex c3(0:NSPC-1) !Complex spectrum of Costas 3
data icos7/2,5,6,0,4,1,3/ !Costas 7x7 tone pattern
data mode64z/-1/
save
if(mode64.ne.mode64z) then
twopi=8.0*atan(1.0)
dfgen=mode64*12000.0/6912.0
k=-1
phi=0.
do j=0,6 !Compute complex Costas waveform
dphi=twopi*icos7(j)*dfgen/4000.0
do i=1,2304
phi=phi + dphi
if(phi.gt.twopi) phi=phi-twopi
k=k+1
cc(k)=cmplx(cos(phi),sin(phi))
enddo
enddo
mode64z=mode64
endif
npts0=54*12000
nfft1=672000
nfft2=nfft1/3
df1=12000.0/nfft1
fac=2.0/nfft1
do i=0,nfft1/2 !Load real data into c0
c0(i)=fac*cmplx(dd(1+2*i),dd(2+2*i))
enddo
call four2a(c0,nfft1,1,-1,0) !Forward r2c FFT
call four2a(c0,nfft2,1,1,1) !Inverse c2c FFT; c0 is analytic sig
npts2=npts0/3 !Downsampled complex data length
nfft3=NSPC
nh3=nfft3/2
df3=4000.0/nfft3
fa=max(nf1,nfqso-ntol)
fb=min(nf2,nfqso+ntol)
ia=max(maxf1,nint(fa/df3))
ib=min(NSPC-1-maxf1,nint(fb/df3))
iz=ib-ia+1
snr=0.
jpk=0
ja=0
jb=6*4000
jstep=200
ka=-maxf1
kb=maxf1
ipk=0
kpk=0
do iter=1,2
do j1=ja,jb,jstep
j2=j1 + 39*2304
j3=j1 + 77*2304
c1=1.e-4*c0(j1:j1+NSPC-1) * conjg(cc)
call four2a(c1,nfft3,1,-1,1)
c2=1.e-4*c0(j2:j2+NSPC-1) * conjg(cc)
call four2a(c2,nfft3,1,-1,1)
c3=1.e-4*c0(j3:j3+NSPC-1) * conjg(cc)
call four2a(c3,nfft3,1,-1,1)
s0=0.
s1=0.
s2=0.
s3=0.
do i=ia,ib
freq=i*df3
s1(i)=real(c1(i))**2 + aimag(c1(i))**2
s2(i)=real(c2(i))**2 + aimag(c2(i))**2
s3(i)=real(c3(i))**2 + aimag(c3(i))**2
enddo
do k=ka,kb
s0b(ia:ib)=s1(ia-k:ib-k) + s2(ia:ib) + s3(ia+k:ib+k)
s0b(:ia-1)=0.
s0b(ib+1:)=0.
nadd=(7*mode64)/2
if(mod(nadd,2).eq.1) nadd=nadd+1 !Make nadd odd
if(nadd.ge.3) call smo(s0b(ia:ib),iz,s0(ia:ib),nadd)
call smo121(s0(ia:ib),iz)
nskip=max(14,2*mode64)
call averms(s0(ia:ib),iz,nskip,ave,rms)
s=(maxval(s0(ia:ib))-ave)/rms
if(s.gt.snr) then
jpk=j1
s0a=s0/rms
snr=s
dtx=jpk/4000.0 - 1.0
ipk0=maxloc(s0(ia:ib))
ipk=ipk0(1)
f0=(ipk+ia-1)*df3
kpk=k
endif
enddo
enddo
ja=max(0,jpk-2*jstep)
jb=min(336000-NSPC,jpk+2*jstep)
jstep=10
enddo
write(17) ia,ib,s0a(ia:ib) !Save data for red curve
close(17)
snrdb=10.0*log10(snr)-39.0
return
end subroutine sync64