subroutine decode1a(dd,newdat,f0,nflip,mode65,nfast,nfsample,xpol, & mycall,hiscall,hisgrid,neme,ndepth,nqd,dphi,ndphi,iloop, & nutc,nkhz,ndf,ipol,ntol,bqra64,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,bqra64 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,nfast,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,nfast,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/nfast j=(dt00+dtbest+2.685)*1378.125 if(nfast.eq.2) j=j-1506 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(nfast.eq.1 .and. mode65.eq.2) jj=2*i-1 if(nfast.eq.2 .and. mode65.eq.4) jj=2*i-1 if(nfast.eq.1 .and. 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 if(nfast.eq.2) dt=dt00 + dtbest + 0.6 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