WSJT-X/map65/libm65/decode1a.f90

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Fortran
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subroutine decode1a(dd,newdat,f0,nflip,mode65,nfsample,xpol, &
mycall,hiscall,hisgrid,neme,ndepth,nqd,dphi,ndphi,iloop, &
nutc,nkhz,ndf,ipol,ntol,bq65,sync2,a,dt,pol,nkv,nhist,nsum,nsave, &
qual,decoded)
! Apply AFC corrections to a candidate JT65 signal, then decode it.
parameter (NMAX=60*96000) !Samples per 60 s
real*4 dd(4,NMAX) !92 MB: raw data from Linrad timf2
complex cx(NMAX/64), cy(NMAX/64) !Data at 1378.125 samples/s
complex c5x(NMAX/256),c5y(NMAX/256) !Data at 344.53125 Hz
complex c5a(512)
complex z
real s2(66,126)
real s3(64,63),sy(63)
real a(5)
logical first,xpol,bq65
character decoded*22
character mycall*12,hiscall*12,hisgrid*6
data first/.true./,jjjmin/1000/,jjjmax/-1000/
data nutc0/-999/,nhz0/-9999999/
save
! Mix sync tone to baseband, low-pass filter, downsample to 1378.125 Hz
dt00=dt
call timer('filbig ',0)
call filbig(dd,NMAX,f0,newdat,nfsample,xpol,cx,cy,n5)
! NB: cx, cy have sample rate 96000*77125/5376000 = 1378.125 Hz
call timer('filbig ',1)
if(nqd.eq.2) goto 900
sqa=0.
sqb=0.
do i=1,n5
sqa=sqa + real(cx(i))**2 + aimag(cx(i))**2
if(xpol) sqb=sqb + real(cy(i))**2 + aimag(cy(i))**2
enddo
sqa=sqa/n5
sqb=sqb/n5
! Find best DF, f1, f2, DT, and pol. Start by downsampling to 344.53125 Hz
if(xpol) then
z=cmplx(cos(dphi),sin(dphi))
cy(:n5)=z*cy(:n5) !Adjust for cable length difference
endif
call timer('fil6521 ',0)
! Add some zeros at start of c5 arrays -- empirical fix for negative DT's
nadd=1089
c5x(:nadd)=0.
call fil6521(cx,n5,c5x(nadd+1),n6)
if(xpol) then
c5y(:nadd)=0.
call fil6521(cy,n5,c5y(nadd+1),n6)
endif
n6=n6+nadd
call timer('fil6521 ',1)
fsample=1378.125/4.
a(5)=dt00
i0=nint((a(5)+0.5)*fsample) - 2 + nadd
if(i0.lt.1) then
write(13,*) 'i0 too small in decode1a:',i0,f0
flush(13)
i0=1
endif
nz=n6+1-i0
! We're looking only at sync tone here... so why not downsample by another
! factor of 1/8, say? Should be a significant execution speed-up.
call timer('afc65b ',0)
! Best fit for DF, f1, f2, pol
call afc65b(c5x(i0),c5y(i0),nz,fsample,nflip,ipol,xpol, &
ndphi,iloop,a,ccfbest,dtbest)
call timer('afc65b ',1)
pol=a(4)/57.2957795
aa=cos(pol)
bb=sin(pol)
sq0=aa*aa*sqa + bb*bb*sqb
sync2=3.7*ccfbest/sq0
! Apply AFC corrections to the time-domain signal
! Now we are back to using the 1378.125 Hz sample rate, enough to
! accommodate the full JT65C bandwidth.
call timer('twkfreq_',0)
call twkfreq_xy(cx,cy,n5,a)
call timer('twkfreq_',1)
! Compute spectrum at best polarization for each half symbol.
! Adding or subtracting a small number (e.g., 5) to j may make it decode.\
! NB: might want to try computing full-symbol spectra (nfft=512, even for
! submodes B and C).
nsym=126
nfft=512
j=(dt00+dtbest+2.685)*1378.125
if(j.lt.0) j=0
call timer('sh_ffts ',0)
! Perhaps should try full-symbol-length FFTs even in B, C sub-modes?
! (Tried this, found no significant difference in decodes.)
do k=1,nsym
! do n=1,mode65
do n=1,1
do i=1,nfft
j=j+1
c5a(i)=aa*cx(j) + bb*cy(j)
enddo
call four2a(c5a,nfft,1,1,1)
if(n.eq.1) then
do i=1,66
! s2(i,k)=real(c5a(i))**2 + aimag(c5a(i))**2
jj=i
if(mode65.eq.2) jj=2*i-1
if(mode65.eq.4) jj=4*i-3
s2(i,k)=real(c5a(jj))**2 + aimag(c5a(jj))**2
enddo
else
do i=1,66
s2(i,k)=s2(i,k) + real(c5a(i))**2 + aimag(c5a(i))**2
enddo
endif
enddo
enddo
call timer('sh_ffts ',1)
flip=nflip
call timer('dec65b ',0)
call decode65b(s2,flip,mycall,hiscall,hisgrid,mode65,neme,ndepth, &
nqd,nkv,nhist,qual,decoded,s3,sy)
dt=dt00 + dtbest + 1.7
call timer('dec65b ',1)
if(nqd.eq.1 .and. decoded.eq.' ') then
nhz=1000*nkhz + ndf
ihzdiff=min(500,ntol)
if(nutc.ne.nutc0 .or. abs(nhz-nhz0).ge.ihzdiff) syncbest=0.
if(sync2.gt.0.99999*syncbest) then
nsave=nsave+1
nsave=mod(nsave-1,64)+1
npol=nint(57.296*pol)
call s3avg(nsave,mode65,nutc,nhz,xdt,npol,ntol,s3,nsum,nkv,decoded)
syncbest=sync2
nhz0=nhz
endif
nutc0=nutc
endif
900 return
end subroutine decode1a