subroutine decode65a(dd,npts,newdat,nqd,f0,nflip,mode65,sync2,a,dt, & nbmkv,nhist,decoded) ! Apply AFC corrections to a candidate JT65 signal, then decode it. parameter (NMAX=60*12000) !Samples per 60 s real*4 dd(NMAX) !92 MB: raw data from Linrad timf2 complex cx(NMAX/8) !Data at 1378.125 samples/s complex c5x(NMAX/32) !Data at 344.53125 Hz complex c5a(512) real s2(66,126) real a(5) logical first character decoded*22 data first/.true./,jjjmin/1000/,jjjmax/-1000/ data 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,npts,f0,newdat,cx,n5,sq0) call timer('filbig ',1) ! NB: cx has sample rate 12000*77125/672000 = 1378.125 Hz ! Find best DF, f1, f2, and DT. Start by downsampling to 344.53125 Hz 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) 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 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, and f2 call afc65b(c5x(i0),nz,fsample,nflip,a,ccfbest,dtbest) call timer('afc65b ',1) sync2=3.7e-4*ccfbest/sq0 !Constant is empirical ! 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 twkfreq65(cx,n5,a) call timer('twkfreq ',1) ! Compute spectrum 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) do k=1,nsym do i=1,nfft j=j+1 c5a(i)=cx(j) enddo call four2a(c5a,nfft,1,1,1) do i=1,66 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 enddo call timer('sh_ffts ',1) call timer('dec65b ',0) call decode65b(s2,nflip,mode65,nqd,nbmkv,nhist,decoded) dt=dt00 + dtbest + 1.7 call timer('dec65b ',1) return end subroutine decode65a