113 lines
3.3 KiB
Plaintext
113 lines
3.3 KiB
Plaintext
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program ft8d
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! Decode FT8 data read from *.wav files.
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! FT8 is a potential mode intended for use at 6m (and maybe HF). It uses an
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! LDPC (174,87) code, 8-FSK modulation, and 15 second T/R sequences. Otherwise
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! should behave like JT65 and JT9 as used on HF bands, except that QSOs are
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! 4 x faster.
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! Reception and Demodulation algorithm:
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! ... tbd ...
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include 'ft8_params.f90'
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parameter(NRECENT=10)
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character*12 recent_calls(NRECENT)
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character message*22,infile*80,datetime*13
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real s(NH1,NHSYM)
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real s1(0:7,ND)
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real ps(0:7)
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real rxdata(3*ND),llr(3*ND) !Soft symbols
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integer ihdr(11)
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integer*2 iwave(NMAX) !Generated full-length waveform
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! integer*1 idat(7)
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integer*1 decoded(KK),apmask(ND),cw(ND)
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nargs=iargc()
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if(nargs.lt.1) then
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print*,'Usage: ft8d file1 [file2 ...]'
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go to 999
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endif
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twopi=8.0*atan(1.0)
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fs=12000.0 !Sample rate
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dt=1.0/fs !Sample interval (s)
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tt=NSPS*dt !Duration of "itone" symbols (s)
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ts=2*NSPS*dt !Duration of OQPSK symbols (s)
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baud=1.0/tt !Keying rate (baud)
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txt=NZ*dt !Transmission length (s)
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do ifile=1,nargs
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call getarg(ifile,infile)
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open(10,file=infile,status='old',access='stream')
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read(10,end=999) ihdr,iwave
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close(10)
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j2=index(infile,'.wav')
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read(infile(j2-6:j2-1),*) nutc
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datetime=infile(j2-13:j2-1)
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call sync8(iwave,xdt,f1,s)
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xsnr=0.
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tstep=0.5*NSPS/12000.0
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df=12000.0/NFFT1
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i0=nint(f1/df)
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j0=nint(xdt/tstep)
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fac=20.0/maxval(s)
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s=fac*s
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j=0
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ia=i0
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ib=i0+14
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do k=1,NN
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if(k.le.7) cycle
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if(k.ge.37 .and. k.le.43) cycle
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if(k.gt.72) cycle
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n=j0+2*(k-1)+1
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if(n.lt.1) cycle
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j=j+1
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s1(0:7,j)=s(ia:ib:2,n)
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enddo
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do j=1,ND
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ps=s1(0:7,j)
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ps=log(ps)
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r1=max(ps(1),ps(3),ps(5),ps(7))-max(ps(0),ps(2),ps(4),ps(6))
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r2=max(ps(2),ps(3),ps(6),ps(7))-max(ps(0),ps(1),ps(4),ps(5))
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r4=max(ps(4),ps(5),ps(6),ps(7))-max(ps(0),ps(1),ps(2),ps(3))
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rxdata(3*j-2)=r4
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rxdata(3*j-1)=r2
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rxdata(3*j)=r1
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enddo
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rxav=sum(rxdata)/ND
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rx2av=sum(rxdata*rxdata)/ND
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rxsig=sqrt(rx2av-rxav*rxav)
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rxdata=rxdata/rxsig
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ss=0.84
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llr=2.0*rxdata/(ss*ss)
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apmask=0
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max_iterations=40
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ifer=0
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call bpdecode174(llr,apmask,max_iterations,decoded,niterations)
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if(niterations.lt.0) then
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write(41,*) llr,apmask,max_iterations,decoded,niterations
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call osd174(llr,2,decoded,niterations,cw)
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write(42,*) llr,apmask,max_iterations,decoded,niterations
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! if(niterations.lt.0) stop
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endif
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nbadcrc=0
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if(niterations.ge.0) call chkcrc12a(decoded,nbadcrc)
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if(niterations.lt.0 .or. nbadcrc.ne.0) ifer=1
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message=' '
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if(ifer.eq.0) then
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call extractmessage174(decoded,message,ncrcflag,recent_calls,nrecent)
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endif
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nsnr=nint(xsnr)
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write(13,1110) datetime,0,nsnr,xdt,freq,message,nfdot
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1110 format(a11,2i4,f6.2,f12.7,2x,a22,i3)
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write(*,1112) datetime(8:13),nsnr,xdt,nint(f1),message
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1112 format(a6,i4,f5.1,i6,2x,a22)
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enddo ! ifile loop
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999 end program ft8d
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