WSJT-X/lib/qra/q65/q65.f90
2021-03-19 09:10:04 -04:00

758 lines
20 KiB
Fortran

module q65
parameter (NSTEP=8) !Number of time bins per symbol in s1, s1a, s1b
parameter (PLOG_MIN=-242.0) !List decoding threshold
integer nsave,nlist,LL0,iz0,jz0
integer listutc(10)
integer apsym0(58),aph10(10)
integer apmask1(78),apsymbols1(78)
integer apmask(13),apsymbols(13)
integer,dimension(22) :: isync = (/1,9,12,13,15,22,23,26,27,33,35, &
38,46,50,55,60,62,66,69,74,76,85/)
integer codewords(63,206)
integer ibwa,ibwb,ncw,nsps,mode_q65,nfa,nfb
integer idfbest,idtbest,ibw,ndistbest,maxiters
integer istep,nsmo,lag1,lag2,npasses,nused,iseq,ncand,nrc
integer i0,j0
integer navg(0:1)
logical lnewdat
real candidates(20,3) !snr, xdt, and f0 of top candidates
real, allocatable :: s1raw(:,:) !Symbol spectra, 1/8-symbol steps
real, allocatable :: s1(:,:) !Symbol spectra w/suppressed peaks
real, allocatable,save :: s1a(:,:,:) !Cumulative symbol spectra
real, allocatable,save :: ccf2(:) !Max CCF(freq) at any lag, single seq
real, allocatable,save :: ccf2_avg(:) !Like ccf2, but for accumulated average
real sync(85) !sync vector
real df,dtstep,dtdec,f0dec,ftol,plog
contains
subroutine q65_dec0(iavg,nutc,iwave,ntrperiod,nfqso,ntol,ndepth,lclearave, &
emedelay,xdt,f0,snr1,width,dat4,snr2,idec)
! Top-level routine in q65 module
! - Compute symbol spectra
! - Attempt sync and q3 decode using all 85 symbols
! - If that fails, try sync with 22 symbols and standard q[0124] decode
! Input: iavg 0 for single-period decode, 1 for average
! iwave(0:nmax-1) Raw data
! ntrperiod T/R sequence length (s)
! nfqso Target frequency (Hz)
! ntol Search range around nfqso (Hz)
! ndepth Requested decoding depth
! lclearave Flag to clear the accumulating array
! emedelay Extra delay for EME signals
! Output: xdt Time offset from nominal (s)
! f0 Frequency of sync tone
! snr1 Relative SNR of sync signal
! width Estimated Doppler spread
! dat4(13) Decoded message as 13 six-bit integers
! snr2 Estimated SNR of decoded signal
! idec Flag for decoding results
! -1 No decode
! 0 No AP
! 1 "CQ ? ?"
! 2 "Mycall ? ?"
! 3 "MyCall HisCall ?"
use packjt77
use timer_module, only: timer
parameter (LN=2176*63) !LN=LL*NN; LL=64*(mode_q65+2), NN=63
integer*2 iwave(0:12000*ntrperiod-1) !Raw data
integer dat4(13)
character*37 decoded
logical first,lclearave
real, allocatable :: s3(:,:) !Data-symbol energies s3(LL,63)
real, allocatable :: ccf1(:) !CCF(freq) at fixed lag (red)
data first/.true./
save first
if(nutc+ndepth.eq.-999) stop !Silence compiler warnings
! Set some parameters and allocate storage for large arrays
irc=-2
nrc=-2
idec=-1
snr1=0.
dat4=0
LL=64*(2+mode_q65)
nfft=nsps
df=12000.0/nfft !Freq resolution = baud
istep=nsps/NSTEP
iz=5000.0/df !Uppermost frequency bin, at 5000 Hz
txt=85.0*nsps/12000.0
jz=(txt+1.0)*12000.0/istep !Number of symbol/NSTEP bins
if(nsps.ge.6912) jz=(txt+2.0)*12000.0/istep !For TR 60 s and higher
ftol=ntol
ia=ntol/df
ia2=max(ia,10*mode_q65,nint(100.0/df))
nsmo=int(0.7*mode_q65*mode_q65)
if(nsmo.lt.1) nsmo=1
if(first) then !Generate the sync vector
sync=-22.0/63.0 !Sync tone OFF
do k=1,22
sync(isync(k))=1.0 !Sync tone ON
enddo
endif
allocate(s3(-64:LL-65,63))
allocate(ccf1(-ia2:ia2))
if(LL.ne.LL0 .or. iz.ne.iz0 .or. jz.ne.jz0 .or. lclearave) then
if(allocated(s1raw)) deallocate(s1raw)
allocate(s1raw(iz,jz))
if(allocated(s1)) deallocate(s1)
allocate(s1(iz,jz))
if(allocated(s1a)) deallocate(s1a)
allocate(s1a(iz,jz,0:1))
if(allocated(ccf2)) deallocate(ccf2)
allocate(ccf2(iz))
if(allocated(ccf2_avg)) deallocate(ccf2_avg)
allocate(ccf2_avg(iz))
s1=0.
s1a=0.
navg=0
LL0=LL
iz0=iz
jz0=jz
lclearave=.false.
endif
ccf1=0.
if(iavg.eq.0) ccf2_avg=0.
dtstep=nsps/(NSTEP*12000.0) !Step size in seconds
lag1=-1.0/dtstep
lag2=1.0/dtstep + 0.9999
if(nsps.ge.3600 .and. emedelay.gt.0) lag2=4.0/dtstep + 0.9999 !Include EME
j0=0.5/dtstep
if(nsps.ge.7200) j0=1.0/dtstep !Nominal start-signal index
s3=0.
if(iavg.eq.0) then
call timer('q65_syms',0)
! Compute symbol spectra with NSTEP time bins per symbol
call q65_symspec(iwave,ntrperiod*12000,iz,jz,s1)
call timer('q65_syms',1)
else
s1=s1a(:,:,iseq)
endif
i0=nint(nfqso/df) !Target QSO frequency
if(i0-64.lt.1 .or. i0-65+LL.gt.iz) go to 900 !Frequency out of range
call pctile(s1(i0-64:i0-65+LL,1:jz),LL*jz,45,base)
s1=s1/base
s1raw=s1
! Apply fast AGC to the symbol spectra
s1max=20.0 !Empirical choice
do j=1,jz !### Maybe wrong way? ###
smax=maxval(s1(i0-64:i0-65+LL,j))
if(smax.gt.s1max) s1(i0-64:i0-65+LL,j)=s1(i0-64:i0-65+LL,j)*s1max/smax
enddo
dat4=0
if(ncw.gt.0 .and. iavg.le.1) then
! Try list decoding via "Deep Likelihood".
call timer('ccf_85 ',0)
! Try to synchronize using all 85 symbols
call q65_ccf_85(s1,iz,jz,nfqso,ia,ia2,ipk,jpk,f0,xdt,imsg_best,ccf1)
call timer('ccf_85 ',1)
call timer('list_dec',0)
call q65_dec_q3(s1,iz,jz,s3,LL,ipk,jpk,snr2,dat4,idec,decoded)
call timer('list_dec',1)
endif
if(iavg.eq.0) then
call q65_ccf_22(s1,iz,jz,nfqso,ipk,jpk,f0a,xdta,ccf2)
endif
! Get 2d CCF and ccf2 using sync symbols only
if(iavg.ge.1) then
call q65_ccf_22(s1,iz,jz,nfqso,ipk,jpk,f0a,xdta,ccf2_avg)
endif
if(idec.lt.0) then
f0=f0a
xdt=xdta
endif
! Estimate rms on ccf2 baseline
call q65_sync_curve(ccf2,1,iz,rms2)
smax=maxval(ccf2)
snr1=0.
if(rms2.gt.0) snr1=smax/rms2
if(idec.le.0) then
! The q3 decode attempt failed. Copy synchronized symbol energies from s1
! into s3 and prepare to try a more general decode.
call q65_s1_to_s3(s1,iz,jz,ipk,jpk,LL,mode_q65,sync,s3)
endif
smax=maxval(ccf1)
! Estimate frequenct spread
i1=-9999
i2=-9999
do i=-ia,ia
if(i1.eq.-9999 .and. ccf1(i).ge.0.5*smax) i1=i
if(i2.eq.-9999 .and. ccf1(-i).ge.0.5*smax) i2=-i
enddo
width=df*(i2-i1)
if(ncw.eq.0) ccf1=0.
! write(*,3001) nutc,iavg,navg(0),sum(ccf2_avg),sum(ccf2)
!3001 format(i4.4,2i4,2f8.2)
call q65_write_red(iz,xdt,ccf2_avg,ccf2)
if(iavg.eq.2) then
call q65_dec_q012(s3,LL,snr2,dat4,idec,decoded)
endif
900 return
end subroutine q65_dec0
subroutine q65_clravg
! Clear the averaging array to start a new average.
if(allocated(s1a)) s1a(:,:,iseq)=0.
navg(iseq)=0
return
end subroutine q65_clravg
subroutine q65_symspec(iwave,nmax,iz,jz,s1)
! Compute symbol spectra with NSTEP time-steps per symbol.
integer*2 iwave(0:nmax-1) !Raw data
real s1(iz,jz)
complex, allocatable :: c0(:) !Complex spectrum of symbol
allocate(c0(0:nsps-1))
nfft=nsps
fac=1/32767.0
do j=1,jz !Compute symbol spectra at step size
i1=(j-1)*istep
i2=i1+nsps-1
k=-1
do i=i1,i2,2 !Load iwave data into complex array c0, for r2c FFT
xx=iwave(i)
yy=iwave(i+1)
k=k+1
c0(k)=fac*cmplx(xx,yy)
enddo
c0(k+1:)=0.
call four2a(c0,nfft,1,-1,0) !r2c FFT
do i=1,iz
s1(i,j)=real(c0(i))**2 + aimag(c0(i))**2
enddo
! For large Doppler spreads, should we smooth the spectra here?
if(nsmo.le.1) nsmo=0
do i=1,nsmo
call smo121(s1(1:iz,j),iz)
enddo
enddo
if(lnewdat) then
navg(iseq)=navg(iseq) + 1
ntc=min(navg(iseq),4) !Averaging time constant in sequences
u=1.0/ntc
s1a(:,:,iseq)=u*s1 + (1.0-u)*s1a(:,:,iseq)
endif
return
end subroutine q65_symspec
subroutine q65_dec_q3(s1,iz,jz,s3,LL,ipk,jpk,snr2,dat4,idec,decoded)
! Copy synchronized symbol energies from s1 into s3, then attempt a q3 decode.
character*37 decoded
integer dat4(13)
real s1(iz,jz)
real s3(-64:LL-65,63)
call q65_s1_to_s3(s1,iz,jz,ipk,jpk,LL,mode_q65,sync,s3)
nsubmode=0
if(mode_q65.eq.2) nsubmode=1
if(mode_q65.eq.4) nsubmode=2
if(mode_q65.eq.8) nsubmode=3
if(mode_q65.eq.16) nsubmode=4
if(mode_q65.eq.32) nsubmode=5
baud=12000.0/nsps
do ibw=ibwa,ibwb
b90=1.72**ibw
b90ts=b90/baud
call q65_dec1(s3,nsubmode,b90ts,esnodb,irc,dat4,decoded)
nrc=irc
if(irc.ge.0) then
snr2=esnodb - db(2500.0/baud) + 3.0 !Empirical adjustment
idec=3
exit
endif
enddo
return
end subroutine q65_dec_q3
subroutine q65_dec_q012(s3,LL,snr2,dat4,idec,decoded)
! Do separate passes attempting q0, q1, q2 decodes.
character*37 decoded
character*78 c78
integer dat4(13)
real s3(-64:LL-65,63)
logical lapcqonly
nsubmode=0
if(mode_q65.eq.2) nsubmode=1
if(mode_q65.eq.4) nsubmode=2
if(mode_q65.eq.8) nsubmode=3
if(mode_q65.eq.16) nsubmode=4
baud=12000.0/nsps
iaptype=0
nQSOprogress=0 !### TEMPORARY ? ###
ncontest=0
lapcqonly=.false.
do ipass=0,npasses !Loop over AP passes
apmask=0 !Try first with no AP information
apsymbols=0
if(ipass.ge.1) then
! Subsequent passes use AP information appropiate for nQSOprogress
call q65_ap(nQSOprogress,ipass,ncontest,lapcqonly,iaptype, &
apsym0,apmask1,apsymbols1)
write(c78,1050) apmask1
1050 format(78i1)
read(c78,1060) apmask
1060 format(13b6.6)
write(c78,1050) apsymbols1
read(c78,1060) apsymbols
endif
do ibw=ibwa,ibwb
b90=1.72**ibw
b90ts=b90/baud
call q65_dec2(s3,nsubmode,b90ts,esnodb,irc,dat4,decoded)
nrc=irc
if(irc.ge.0) then
snr2=esnodb - db(2500.0/baud) + 3.0 !Empirical adjustment
idec=iaptype
go to 100
endif
enddo
enddo
100 return
end subroutine q65_dec_q012
subroutine q65_ccf_85(s1,iz,jz,nfqso,ia,ia2,ipk,jpk,f0,xdt,imsg_best,ccf1)
! Attempt synchronization using all 85 symbols, in advance of an
! attempt at q3 decoding. Return ccf1 for the "red sync curve".
real s1(iz,jz)
real, allocatable :: ccf(:,:) !CCF(freq,lag)
real ccf1(-ia2:ia2)
integer ijpk(2)
integer itone(85)
allocate(ccf(-ia2:ia2,-53:214))
ipk=0
jpk=0
ccf_best=0.
imsg_best=-1
do imsg=1,ncw
i=1
k=0
do j=1,85
if(j.eq.isync(i)) then
i=i+1
itone(j)=0
else
k=k+1
itone(j)=codewords(k,imsg) + 1
endif
enddo
! Compute 2D ccf using all 85 symbols in the list message
ccf=0.
iia=200.0/df
do lag=lag1,lag2
do k=1,85
j=j0 + NSTEP*(k-1) + 1 + lag
if(j.ge.1 .and. j.le.jz) then
do i=-ia2,ia2
ii=i0+mode_q65*itone(k)+i
if(ii.ge.iia .and. ii.le.iz) ccf(i,lag)=ccf(i,lag) + s1(ii,j)
enddo
endif
enddo
enddo
ccfmax=maxval(ccf(-ia:ia,:))
if(ccfmax.gt.ccf_best) then
ccf_best=ccfmax
ijpk=maxloc(ccf(-ia:ia,:))
ipk=ijpk(1)-ia-1
jpk=ijpk(2)-53-1
f0=nfqso + ipk*df
xdt=jpk*dtstep
imsg_best=imsg
ccf1=ccf(:,jpk)
endif
enddo ! imsg
deallocate(ccf)
return
end subroutine q65_ccf_85
subroutine q65_ccf_22(s1,iz,jz,nfqso,ipk,jpk,f0,xdt,ccf2)
! Attempt synchronization using only the 22 sync symbols. Return ccf2
! for the "orange sync curve".
real s1(iz,jz)
real ccf2(iz) !Orange sync curve
real, allocatable :: xdt2(:)
integer, allocatable :: indx(:)
allocate(xdt2(iz))
allocate(indx(iz))
ccfbest=0.
ibest=0
lagpk=0
lagbest=0
do i=1,iz
ccfmax=0.
do lag=lag1,lag2
ccft=0.
do k=1,85
n=NSTEP*(k-1) + 1
j=n+lag+j0
if(j.ge.1 .and. j.le.jz) then
ccft=ccft + sync(k)*s1(i,j)
endif
enddo
if(ccft.gt.ccfmax) then
ccfmax=ccft
lagpk=lag
endif
enddo
ccf2(i)=ccfmax
xdt2(i)=lagpk*dtstep
if(ccfmax.gt.ccfbest .and. abs(i*df-nfqso).le.ftol) then
ccfbest=ccfmax
ibest=i
lagbest=lagpk
endif
enddo
! Parameters for the top candidate:
ipk=ibest - i0
jpk=lagbest
f0=nfqso + ipk*df
xdt=jpk*dtstep
! Save parameters for best candidates
i1=max(nfa,100)/df
i2=min(nfb,4900)/df
jzz=i2-i1+1
call pctile(ccf2(i1:i2),jzz,40,base)
ccf2=ccf2/base
call indexx(ccf2(i1:i2),jzz,indx)
ncand=0
maxcand=20
do j=1,20
i=indx(jzz-j+1)+i1-1
if(ccf2(i).lt.3.3) exit !Candidate limit
f=i*df
if(f.ge.(nfqso-ftol) .and. f.le.(nfqso+ftol)) cycle !Looked here already
i3=max(1, i-mode_q65)
i4=min(iz,i+mode_q65)
biggest=maxval(ccf2(i3:i4))
if(ccf2(i).ne.biggest) cycle
ncand=ncand+1
candidates(ncand,1)=ccf2(i)
candidates(ncand,2)=xdt2(i)
candidates(ncand,3)=f
if(ncand.ge.maxcand) exit
enddo
return
end subroutine q65_ccf_22
subroutine q65_dec1(s3,nsubmode,b90ts,esnodb,irc,dat4,decoded)
! Attmpt a full-AP list decode.
use packjt77
real s3(1,1) !Silence compiler warning that wants to see a 2D array
real s3prob(0:63,63) !Symbol-value probabilities
integer dat4(13)
character c77*77,decoded*37
logical unpk77_success
nFadingModel=1
decoded=' '
call q65_intrinsics_ff(s3,nsubmode,b90ts,nFadingModel,s3prob)
call q65_dec_fullaplist(s3,s3prob,codewords,ncw,esnodb,dat4,plog,irc)
if(sum(dat4).le.0) irc=-2
if(irc.ge.0 .and. plog.gt.PLOG_MIN) then
write(c77,1000) dat4(1:12),dat4(13)/2
1000 format(12b6.6,b5.5)
call unpack77(c77,0,decoded,unpk77_success) !Unpack to get msgsent
else
irc=-1
endif
nrc=irc
return
end subroutine q65_dec1
subroutine q65_dec2(s3,nsubmode,b90ts,esnodb,irc,dat4,decoded)
! Attempt a q0, q1, or q2 decode using spcified AP information.
use packjt77
real s3(iz0,jz0) !Silence compiler warning that wants to see a 2D array
real s3prob(0:63,63) !Symbol-value probabilities
integer dat4(13)
character c77*77,decoded*37
logical unpk77_success
nFadingModel=1
decoded=' '
call q65_intrinsics_ff(s3,nsubmode,b90ts,nFadingModel,s3prob)
call q65_dec(s3,s3prob,APmask,APsymbols,maxiters,esnodb,dat4,irc)
if(sum(dat4).le.0) irc=-2
nrc=irc
if(irc.ge.0) then
write(c77,1000) dat4(1:12),dat4(13)/2
1000 format(12b6.6,b5.5)
call unpack77(c77,0,decoded,unpk77_success) !Unpack to get msgsent
endif
return
end subroutine q65_dec2
subroutine q65_s1_to_s3(s1,iz,jz,ipk,jpk,LL,mode_q65,sync,s3)
! Copy synchronized symbol energies from s1 (or s1a) into s3.
real s1(iz,jz)
real s3(-64:LL-65,63)
real sync(85) !sync vector
i1=i0+ipk-64 + mode_q65
i2=i1+LL-1
if(i1.ge.1 .and. i2.le.iz) then
j=j0+jpk-7
n=0
do k=1,85
j=j+8
if(sync(k).gt.0.0) then
cycle
endif
n=n+1
if(j.ge.1 .and. j.le.jz) s3(-64:LL-65,n)=s1(i1:i2,j)
enddo
endif
call q65_bzap(s3,LL) !Zap birdies
return
end subroutine q65_s1_to_s3
subroutine q65_write_red(iz,xdt,ccf2_avg,ccf2)
! Write data for the red and orange sync curves to LU 17.
real ccf2_avg(iz)
real ccf2(iz)
call q65_sync_curve(ccf2_avg,1,iz,rms1)
call q65_sync_curve(ccf2,1,iz,rms2)
rewind 17
write(17,1000) xdt,minval(ccf2_avg),maxval(ccf2_avg)
do i=max(1,nint(nfa/df)),min(iz,int(nfb/df))
freq=i*df
y1=ccf2_avg(i)
if(y1.gt.10.0) y1=10.0 + 2.0*log10(y1/10.0)
y2=ccf2(i)
if(y2.gt.10.0) y2=10.0 + 2.0*log10(y2/10.0)
write(17,1000) freq,y1,y2
1000 format(3f10.3)
enddo
flush(17)
return
end subroutine q65_write_red
subroutine q65_sync_curve(ccf1,ia,ib,rms1)
! Condition the red or orange sync curve for plotting.
real ccf1(ia:ib)
ic=(ib-ia)/8;
nsum=2*(ic+1)
base1=(sum(ccf1(ia:ia+ic)) + sum(ccf1(ib-ic:ib)))/nsum
ccf1=ccf1-base1
sq=dot_product(ccf1(ia:ia+ic),ccf1(ia:ia+ic)) + &
dot_product(ccf1(ib-ic:ib),ccf1(ib-ic:ib))
rms1=0.
if(nsum.gt.0) rms1=sqrt(sq/nsum)
if(rms1.gt.0.0) ccf1=ccf1/rms1
! smax1=maxval(ccf1)
! if(smax1.gt.10.0) ccf1=10.0*ccf1/smax1
return
end subroutine q65_sync_curve
subroutine q65_bzap(s3,LL)
parameter (NBZAP=15)
real s3(-64:LL-65,63)
integer ipk1(1)
integer, allocatable :: hist(:)
allocate(hist(-64:LL-65))
hist=0
do j=1,63
ipk1=maxloc(s3(:,j))
i=ipk1(1) - 65
hist(i)=hist(i)+1
enddo
if(maxval(hist).gt.NBZAP) then
do i=-64,LL-65
if(hist(i).gt.NBZAP) s3(i,1:63)=1.0
enddo
endif
return
end subroutine q65_bzap
subroutine q65_snr(dat4,dtdec,f0dec,mode_q65,nused,snr2)
! Estimate SNR of a decoded transmission by aligning the spectra of
! all 85 symbols.
integer dat4(13)
integer codeword(63)
integer itone(85)
real, allocatable :: spec(:)
allocate(spec(iz0))
call q65_enc(dat4,codeword)
i=1
k=0
do j=1,85
if(j.eq.isync(i)) then
i=i+1
itone(j)=0
else
k=k+1
itone(j)=codeword(k) + 1
endif
enddo
spec=0.
lagpk=nint(dtdec/dtstep)
do k=1,85
j=j0 + NSTEP*(k-1) + 1 + lagpk
if(j.ge.1 .and. j.le.jz0) then
do i=1,iz0
ii=i+mode_q65*itone(k)
if(ii.ge.1 .and. ii.le.iz0) spec(i)=spec(i) + s1raw(ii,j)
enddo
endif
enddo
i0=nint(f0dec/df)
nsum=max(10*mode_q65,nint(50.0/df))
ia=max(1,i0-2*nsum)
ib=min(iz0,i0+2*nsum)
sum1=sum(spec(ia:ia+nsum-1))
sum2=sum(spec(ib-nsum+1:ib))
avg=(sum1+sum2)/(2.0*nsum)
spec=spec/avg !Baseline level is now 1.0
smax=maxval(spec(ia:ib))
sig_area=sum(spec(ia+nsum:ib-nsum)-1.0)
w_equiv=sig_area/(smax-1.0)
snr2=db(max(1.0,sig_area)) - db(2500.0/df)
if(nused.eq.2) snr2=snr2 - 2.0
if(nused.eq.3) snr2=snr2 - 2.9
if(nused.ge.4) snr2=snr2 - 3.5
! do i=ia,ib
! write(71,3071) i*df,spec(i),db(spec(i))
!3071 format(3f10.3)
! enddo
! flush(71)
return
end subroutine q65_snr
subroutine q65_hist(if0,msg0,dxcall,dxgrid)
! Save the MAXHIST most receent decodes, and their f0 values; or, if
! dxcall is present, look up the most recent dxcall and dxgrid at the
! specified f0.
parameter (MAXHIST=100)
integer,intent(in) :: if0 !Audio freq of decode
character(len=37),intent(in),optional :: msg0 !Decoded message
character(len=12),intent(out),optional :: dxcall !Second callsign in message
character(len=6),intent(out),optional :: dxgrid !Third word in msg, if grid
character*6 g1
character*37 msg(MAXHIST) !Saved messages
integer nf0(MAXHIST) !Saved frequencies
logical isgrid !Statement function
data nhist/0/
save nhist,nf0,msg
isgrid(g1)=g1(1:1).ge.'A' .and. g1(1:1).le.'R' .and. g1(2:2).ge.'A' .and. &
g1(2:2).le.'R' .and. g1(3:3).ge.'0' .and. g1(3:3).le.'9' .and. &
g1(4:4).ge.'0' .and. g1(4:4).le.'9' .and. g1(1:4).ne.'RR73'
if(present(dxcall)) go to 100 !This is a lookup request
if(nhist.eq.MAXHIST) then
nf0(1:MAXHIST-1)=nf0(2:MAXHIST) !List is full, must make room
msg(1:MAXHIST-1)=msg(2:MAXHIST)
nhist=MAXHIST-1
endif
nhist=nhist+1 !Insert msg0 at end of list
nf0(nhist)=if0
msg(nhist)=msg0
go to 900
100 dxcall=' ' !This is a lookup request
dxgrid=' '
! Look for a decode close to if0, starting with most recent ones
do i=nhist,1,-1
if(abs(nf0(i)-if0).gt.10) cycle
i1=index(msg(i),' ')
if(i1.ge.4 .and. i1.le.13) then
i2=index(msg(i)(i1+1:),' ') + i1
dxcall=msg(i)(i1+1:i2-1) !Extract dxcall
g1=msg(i)(i2+1:i2+4)
if(isgrid(g1)) dxgrid=g1(1:4) !Extract dxgrid
exit
endif
enddo
900 return
end subroutine q65_hist
end module q65