subroutine decode1a(id,newdat,nfilt,freq,nflip,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) complex c5a(256), c5b(256) real s2(256,126) real a(5) real*8 samratio integer resample logical first character decoded*22 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) if(nfilt.eq.1) then call filbig(id,NMAX,f0,newdat,cx,cy,n5) joff=0 else call fil659(id,NMAX,f0,c2x,c2y,n2) !Pass 1: mix and filter both pol'ns call fil658(c2x,n2,c3x,n3) !Pass 2 call fil658(c2y,n2,c3y,n3) call fil658(c3x,n3,c4x,n4) !Pass 3 call fil658(c3y,n3,c4y,n4) joff=-8 C Resample from 96000/64 = 1500 Hz to 1378.125 Hz C Converter type: 0=Best quality sinc (band limited), BW=97% C 1=medium quality sinc, BW=90% C 2=fastest sinc, BW=80% C 3=stepwise (very fast) C 4=linear (very fast) nconv_type=2 !### test! ### nchans=2 samratio=1378.125d0/1500.d0 i1=resample(c4x,n4,nconv_type,nchans,samratio,cx,n5) i2=resample(c4y,n4,nconv_type,nchans,samratio,cy,n5) endif 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,c5y,n6) 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 ip0=ipol nflip=1 call afc65b(c5x(i0),c5y(i0),nz,fsample,nflip,ipol,a,dt, + ccfbest,dtbest) nflip=-1 ipol=ip0 call afc65b(c5x(i0),c5y(i0),nz,fsample,nflip,ipol,a,dt, + ccfbest2,dtbest) if(ccfbest2.lt.ccfbest) then nflip=1 ipol=ip0 call afc65b(c5x(i0),c5y(i0),nz,fsample,nflip,ipol,a,dt, + ccfbest,dtbest) else ccfbest=ccfbest endif 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,nkv,nhist,qual,decoded) dt=dt00 + dtbest return end