WSJT-X/decode1a.f

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subroutine decode1a(id,newdat,freq,nflip,
+ mycall,hiscall,hisgrid,neme,ndepth,nqd,dphi,ndphi,
+ ipol,sync2,a,dt,pol,nkv,nhist,qual,decoded)
C Apply AFC corrections to a candidate JT65 signal, and then try
C to decode it.
parameter (NFFT1=77760,NFFT2=2430)
parameter (NMAX=60*96000) !Samples per 60 s
integer*2 id(4,NMAX) !46 MB: raw data from Linrad timf2
complex c2x(NMAX/4), c2y(NMAX/4) !After 1/4 filter and downsample
complex c3x(NMAX/16),c3y(NMAX/16) !After 1/16 filter and downsample
complex c4x(NMAX/64),c4y(NMAX/64) !After 1/64 filter and downsample
complex cx(NMAX/64), cy(NMAX/64) !Data at 1378.125 samples/s
complex c5x(NMAX/256),c5y(NMAX/256),c5y0(NMAX/256)
complex c5a(256), c5b(256)
complex z
real s2(256,126)
real a(5)
real*8 samratio
logical first
character decoded*22
character mycall*12,hiscall*12,hisgrid*6
data first/.true./,jjjmin/1000/,jjjmax/-1000/
save
C Mix sync tone to baseband, low-pass filter, and decimate by 64
dt00=dt
C If freq=125.0 kHz, f0=48000 Hz.
f0=1000*(freq-77.0) !Freq of sync tone (0-96000 Hz)
call filbig(id,NMAX,f0,newdat,cx,cy,n5)
joff=0
sqa=0.
sqb=0.
do i=1,n5
sqa=sqa + real(cx(i))**2 + aimag(cx(i))**2
sqb=sqb + real(cy(i))**2 + aimag(cy(i))**2
enddo
sqa=sqa/n5
sqb=sqb/n5
C Find best DF, f1, f2, DT, and pol
! a(5)=dt00
! fsample=1378.125
! i0=nint((a(5)+0.5)*fsample)
! if(i0.lt.1) i0=1
! nz=n5+1-i0
! call afc65b(cx(i0),cy(i0),nz,fsample,nflip,ipol,a,dt,
! + ccfbest,dtbest)
call fil6521(cx,n5,c5x,n6)
call fil6521(cy,n5,c5y0,n6)
! Adjust for cable length difference:
z=cmplx(cos(dphi),sin(dphi))
do i=1,n6
c5y(i)=z*c5y0(i)
enddo
fsample=1378.125/4.
a(5)=dt00
i0=nint((a(5)+0.5)*fsample) - 2
if(i0.lt.1) i0=1
nz=n6+1-i0
call afc65b(c5x(i0),c5y(i0),nz,fsample,nflip,ipol,a,dt,
+ ccfbest,dtbest)
pol=a(4)/57.2957795
aa=cos(pol)
bb=sin(pol)
sq0=aa*aa*sqa + bb*bb*sqb
sync2=3.7*ccfbest/sq0
C Apply AFC corrections to the time-domain signal
call twkfreq(cx,cy,n5,a)
C Compute spectrum at best polarization for each half symbol.
C Adding or subtracting a small number (e.g., 5) to j may make it decode.
nsym=126
nfft=256
j=(dt00+dtbest+2.685)*1378.125 + joff
if(j.lt.0) j=0
j0=j
do k=1,nsym
do i=1,nfft
j=j+1
c5a(i)=aa*cx(j) + bb*cy(j)
enddo
call four2a(c5a,nfft,1,1,1)
do i=1,nfft
j=j+1
c5b(i)=aa*cx(j) + bb*cy(j)
enddo
call four2a(c5b,nfft,1,1,1)
do i=1,256
s2(i,k)=real(c5a(i))**2 + aimag(c5a(i))**2 +
+ real(c5b(i))**2 + aimag(c5b(i))**2
enddo
enddo
flip=nflip
call decode65b(s2,flip,mycall,hiscall,hisgrid,neme,ndepth,
+ nqd,nkv,nhist,qual,decoded)
dt=dt00 + dtbest
return
end