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Improvements to a7 decoding for FT8.
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Joe Taylor
parent
48b1ad1e46
commit
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209
lib/ft8_a7.f90
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209
lib/ft8_a7.f90
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@ -0,0 +1,209 @@
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module ft8_a7
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parameter(MAXDEC=100)
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! For the following three arrays
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! First index i=decode number in this sequence
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! Second index j=0 or 1 for even or odd sequence
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! Third index k=0 or 1 for previous or current tally for this j
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real dt0(MAXDEC,0:1,0:1) !dt0(i,j,k)
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real f0(MAXDEC,0:1,0:1) !f0(i,j,k)
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character*37 msg0(MAXDEC,0:1,0:1) !msg0(i,j,k)
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integer jseq !even=0, odd=1
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integer ndec(0:1,0:1) !ndec(j,k)
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data ndec/4*0/,jseq/0/
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contains
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subroutine ft8_a7_save(nutc,dt,f,msg)
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use packjt77
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character*37 msg,msg1
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character*13 w(19)
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character*4 g4
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integer nw(19)
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logical isgrid4
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! Statement function:
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isgrid4(g4)=(len_trim(g4).eq.4 .and. &
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ichar(g4(1:1)).ge.ichar('A') .and. ichar(g4(1:1)).le.ichar('R') .and. &
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ichar(g4(2:2)).ge.ichar('A') .and. ichar(g4(2:2)).le.ichar('R') .and. &
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ichar(g4(3:3)).ge.ichar('0') .and. ichar(g4(3:3)).le.ichar('9') .and. &
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ichar(g4(4:4)).ge.ichar('0') .and. ichar(g4(4:4)).le.ichar('9'))
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j=mod(nutc/5,2) !j is 0 or 1 for odd/even sequence
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jseq=j
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! Add this decode to current table for this sequence
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ndec(j,1)=ndec(j,1)+1 !Number of decodes in this sequence
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i=ndec(j,1) !i is pointer to new table entry
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if(i.ge.MAXDEC-1) return !Prevent table overflow
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if(index(msg,'<...>').ge.1) return !Don't save an unknown hashcall
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dt0(i,j,1)=dt !Save dt in table
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f0(i,j,1)=f !Save f in table
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f0(i+1,j,1)=-99.0 !Flag after last entry in current table
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call split77(msg,nwords,nw,w) !Parse msg into words
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msg0(i,j,1)=trim(w(1))//' '//trim(w(2))
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if(w(1)(1:3).eq.'CQ ' .and. nw(2).le.2) then
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msg0(i,j,1)='CQ '//trim(w(2))//' '//trim(w(3))
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endif
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msg1=msg0(i,j,1) !Message without grid
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nn=len(trim(msg1)) !Message length without grid
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if(isgrid4(w(nwords))) msg0(i,j,1)=trim(msg0(i,j,1))//' '//trim(w(nwords))
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! If a transmission at this frequency with this message fragment
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! was decoded in the previous sequence, flag it as "DO NOT USE" because
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! we have already decoded that station's next transmission.
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call split77(msg1,nwords,nw,w) !Parse msg into words
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do i=1,ndec(j,0)
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if(f0(i,j,0).le.-98.0) cycle
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i2=index(msg0(i,j,0),' '//trim(w(2)))
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if(abs(f-f0(i,j,0)).lt.2.0 .and. i2.ge.3) then
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f0(i,j,0)=-98.0 !Remove from list of to-be-tried a7 decodes
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endif
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enddo
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return
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end subroutine ft8_a7_save
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subroutine ft8_dec7(cd,xdt0,f0,msg0,xdt,xsnr,msgbest,snr7,snr7b)
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! Get a7 (q3-style) decodes for FT8.
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use packjt77
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parameter(NN=79,NSPS=32)
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parameter(NWAVE=NN*NSPS) !2528
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parameter(NZ=3200,NLAGS=NZ-NWAVE)
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parameter(MAXMSG=206)
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character*12 call_1,call_2
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character*13 w(19)
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character*4 grid4
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character*37 msg0,msg,msgbest,msgsent
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character c77*77
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complex cwave(0:NWAVE-1)
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complex cd(0:NZ-1)
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complex z
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real xjunk(NWAVE)
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real ccf(0:NLAGS-1)
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real ccfmsg(MAXMSG)
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integer itone(NN)
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integer nw(19)
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integer*1 msgbits(77)
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logical std_1,std_2
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if(xdt0.eq.-999.0) return !Silence compiler warning
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snr7=0.
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ccfmsg=0.
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call split77(msg0,nwords,nw,w) !Parse msg0 into words
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call_1=w(1)(1:12)
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call_2=w(2)(1:12)
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grid4=w(3)(1:4)
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if(call_1(1:3).eq.'CQ_') call_1(3:3)=' '
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call stdcall(call_1,std_1)
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if(call_1(1:3).eq.'CQ ') std_1=.true.
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call stdcall(call_2,std_2)
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fs=200.0 !Sample rate (Hz)
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bt=2.0
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ccfbest=0.
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lagbest=-1
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imsgbest=1
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do imsg=1,MAXMSG
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msg=trim(call_1)//' '//trim(call_2)
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i=imsg
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if(call_1(1:3).eq.'CQ ' .and. i.ne.5) msg='CQ0XYZ '//trim(call_2)
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if(.not.std_1) then
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if(i.eq.1 .or. i.ge.6) msg='<'//trim(call_1)//'> '//trim(call_2)
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if(i.ge.2 .and. i.le.4) msg=trim(call_1)//' <'//trim(call_2)//'>'
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else if(.not.std_2) then
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if(i.le.4 .or. i.eq.6) msg='<'//trim(call_1)//'> '//trim(call_2)
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if(i.ge.7) msg=trim(call_1)//' <'//trim(call_2)//'>'
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endif
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j0=len(trim(msg))+2
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if(i.eq.2) msg(j0:j0+2)='RRR'
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if(i.eq.3) msg(j0:j0+3)='RR73'
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if(i.eq.4) msg(j0:j0+1)='73'
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if(i.eq.5) then
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if(std_2) then
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msg='CQ '//trim(call_2)
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if(call_1(3:3).eq.'_') msg=trim(call_1)//' '//trim(call_2)
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if(grid4.ne.'RR73') msg=trim(msg)//' '//grid4
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endif
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if(.not.std_2) msg='CQ '//trim(call_2)
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endif
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if(i.eq.6 .and. std_2) msg(j0:j0+3)=grid4
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if(i.ge.7) then
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isnr = -50 + (i-7)/2
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if(iand(i,1).eq.1) then
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write(msg(j0:j0+2),'(i3.2)') isnr
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if(msg(j0:j0).eq.' ') msg(j0:j0)='+'
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else
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write(msg(j0:j0+3),'("R",i3.2)') isnr
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if(msg(j0+1:j0+1).eq.' ') msg(j0+1:j0+1)='+'
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endif
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endif
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! Source-encode, then get itone()
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i3=-1
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n3=-1
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call pack77(msg,i3,n3,c77)
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call genft8(msg,i3,n3,msgsent,msgbits,itone)
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! Generate complex cwave
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f00=0.0
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call gen_ft8wave(itone,NN,NSPS,bt,fs,f00,cwave,xjunk,1,NWAVE)
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lagmax=-1
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ccfmax=0.
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nsum=32*2
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lag0=200.0*(xdt0+0.5)
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lag1=max(0,lag0-20)
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lag2=min(nlags-1,lag0+20)
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do lag=lag1,lag2
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z=0.
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s=0.
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do i=0,NWAVE-1
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z=z + cd(i+lag)*conjg(cwave(i))
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if(mod(i,nsum).eq.nsum-1 .or. i.eq.NWAVE-1) then
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s=s + abs(z)
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z=0.
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endif
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enddo
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ccf(lag)=s
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if(ccf(lag).gt.ccfmax) then
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ccfmax=ccf(lag)
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lagmax=lag
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endif
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enddo ! lag
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ccfmsg(imsg)=ccfmax
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if(ccfmax.gt.ccfbest) then
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ccfbest=ccfmax
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lagbest=lagmax
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msgbest=msg
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imsgbest=imsg
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endif
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enddo ! imsg
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call pctile(ccfmsg,MAXMSG,50,base)
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call pctile(ccfmsg,MAXMSG,84,sigma)
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sigma=sigma-base
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if(sigma.eq.0.0) sigma=1.0
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ccfmsg=(ccfmsg-base)/sigma
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xdt=lagbest/200.0 - 0.5
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snr7=maxval(ccfmsg)
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ccfmsg(imsgbest)=0.
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snr7b=snr7/maxval(ccfmsg)
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if(index(msgbest,'CQ0XYZ').ge.1) snr7=0.
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xsnr=-99.0
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if(snr7.gt.4.0) xsnr=db(snr7)-24.0
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return
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end subroutine ft8_dec7
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end module ft8_a7
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@ -237,17 +237,24 @@ contains
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do i=1,ndec(jseq,0)
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if(f0(i,jseq,0).eq.-99.0) exit
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if(f0(i,jseq,0).eq.-98.0) cycle
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if(index(msg0(i,jseq,0),'<').ge.1) cycle !### Temporary ###
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call ft8_downsample(dd,newdat,f0(i,jseq,0),cd0)
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call ft8_dec7(cd0,dt0(i,jseq,0),f0(i,jseq,0),msg0(i,jseq,0), &
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xdt,xsnr,msg37)
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if(xsnr.gt.-99.0) then
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if(associated(this%callback)) then
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nsnr=nint(xsnr)
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f1=f0(i,jseq,0)
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iaptype=7
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qual=1.0
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call this%callback(sync,nsnr,xdt,f1,msg37,iaptype,qual)
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endif
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xdt,xsnr,msg37,snr7,snr7b)
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ddt=xdt-dt0(i,jseq,0)
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write(41,3041) nutc,snr7,snr7b,xdt,ddt,nint(f0(i,jseq,0)),trim(msg37)
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3041 format(i6.6,3f7.2,2f6.2,i5,2x,a)
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if(snr7.lt.6.0 .or. snr7b.lt.1.8) cycle
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write(42,3041) nutc,snr7,snr7b,xdt,ddt,nint(f0(i,jseq,0)),trim(msg37)
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flush(41)
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flush(42)
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if(xsnr.gt.-99.0 .and. associated(this%callback)) then
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nsnr=xsnr
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f1=f0(i,jseq,0)
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iaptype=7
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qual=1.0
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call this%callback(sync,nsnr,xdt,f1,msg37,iaptype,qual)
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! Call subtract here?
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endif
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newdat=.false.
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enddo
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