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Jordan Sherer
2018-08-05 11:33:30 -04:00
parent 8f8772f1bd
commit 62899069bf
1222 changed files with 70382 additions and 406763 deletions
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.svn/pristine/ee/ee7d8e3f71453fe6fa1e0849cf1d2f5bc1d84ae6.svn-base
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subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,lapon,napwid, &
lsubtract,nagain,iaptype,mygrid6,bcontest,sync0,f1,xdt,xbase,apsym, &
nharderrors,dmin,nbadcrc,ipass,iera,message,xsnr)
use timer_module, only: timer
include 'ft8_params.f90'
parameter(NRECENT=10,NP2=2812)
character message*22,msgsent*22
character*12 recent_calls(NRECENT)
character*6 mygrid6
logical bcontest
real a(5)
real s1(0:7,ND),s2(0:7,NN),s1sort(8*ND)
real ps(0:7),psl(0:7)
real bmeta(3*ND),bmetb(3*ND),bmetap(3*ND)
real llr(3*ND),llra(3*ND),llr0(3*ND),llr1(3*ND),llrap(3*ND) !Soft symbols
real dd0(15*12000)
integer*1 decoded(KK),apmask(3*ND),cw(3*ND)
integer*1 msgbits(KK)
integer apsym(KK)
integer mcq(28),mde(28),mrrr(16),m73(16),mrr73(16)
integer itone(NN)
integer indxs1(8*ND)
integer icos7(0:6),ip(1)
integer nappasses(0:5) ! the number of decoding passes to use for each QSO state
integer naptypes(0:5,4) ! (nQSOProgress, decoding pass) maximum of 4 passes for now
complex cd0(3200)
complex ctwk(32)
complex csymb(32)
logical first,newdat,lsubtract,lapon,nagain
equivalence (s1,s1sort)
data icos7/2,5,6,0,4,1,3/
data mcq/1,1,1,1,1,0,1,0,0,0,0,0,1,0,0,0,0,0,1,1,0,0,0,1,1,0,0,1/
data mrrr/0,1,1,1,1,1,1,0,1,1,0,0,1,1,1,1/
data m73/0,1,1,1,1,1,1,0,1,1,0,1,0,0,0,0/
data mde/1,1,1,1,1,1,1,1,0,1,1,0,0,1,0,0,0,0,0,1,1,1,0,1,0,0,0,1/
data mrr73/0,0,0,0,0,0,1,0,0,0,0,1,0,1,0,1/
data first/.true./
save nappasses,naptypes
if(first) then
mcq=2*mcq-1
mde=2*mde-1
mrrr=2*mrrr-1
m73=2*m73-1
mrr73=2*mrr73-1
nappasses(0)=2
nappasses(1)=2
nappasses(2)=2
nappasses(3)=4
nappasses(4)=4
nappasses(5)=3
! iaptype
!------------------------
! 1 CQ ??? ???
! 2 MyCall ??? ???
! 3 MyCall DxCall ???
! 4 MyCall DxCall RRR
! 5 MyCall DxCall 73
! 6 MyCall DxCall RR73
! 7 ??? DxCall ???
naptypes(0,1:4)=(/1,2,0,0/)
naptypes(1,1:4)=(/2,3,0,0/)
naptypes(2,1:4)=(/2,3,0,0/)
naptypes(3,1:4)=(/3,4,5,6/)
naptypes(4,1:4)=(/3,4,5,6/)
naptypes(5,1:4)=(/3,1,2,0/) !?
first=.false.
endif
max_iterations=30
nharderrors=-1
fs2=12000.0/NDOWN
dt2=1.0/fs2
twopi=8.0*atan(1.0)
delfbest=0.
ibest=0
call timer('ft8_down',0)
call ft8_downsample(dd0,newdat,f1,cd0) !Mix f1 to baseband and downsample
call timer('ft8_down',1)
i0=nint((xdt+0.5)*fs2) !Initial guess for start of signal
smax=0.0
do idt=i0-8,i0+8 !Search over +/- one quarter symbol
call sync8d(cd0,idt,ctwk,0,sync)
if(sync.gt.smax) then
smax=sync
ibest=idt
endif
enddo
xdt2=ibest*dt2 !Improved estimate for DT
! Now peak up in frequency
i0=nint(xdt2*fs2)
smax=0.0
do ifr=-5,5 !Search over +/- 2.5 Hz
delf=ifr*0.5
dphi=twopi*delf*dt2
phi=0.0
do i=1,32
ctwk(i)=cmplx(cos(phi),sin(phi))
phi=mod(phi+dphi,twopi)
enddo
call sync8d(cd0,i0,ctwk,1,sync)
if( sync .gt. smax ) then
smax=sync
delfbest=delf
endif
enddo
a=0.0
a(1)=-delfbest
call twkfreq1(cd0,NP2,fs2,a,cd0)
xdt=xdt2
f1=f1+delfbest !Improved estimate of DF
call sync8d(cd0,i0,ctwk,2,sync)
j=0
do k=1,NN
i1=ibest+(k-1)*32
csymb=cmplx(0.0,0.0)
if( i1.ge.1 .and. i1+31 .le. NP2 ) csymb=cd0(i1:i1+31)
call four2a(csymb,32,1,-1,1)
s2(0:7,k)=abs(csymb(1:8))/1e3
enddo
! sync quality check
is1=0
is2=0
is3=0
do k=1,7
ip=maxloc(s2(:,k))
if(icos7(k-1).eq.(ip(1)-1)) is1=is1+1
ip=maxloc(s2(:,k+36))
if(icos7(k-1).eq.(ip(1)-1)) is2=is2+1
ip=maxloc(s2(:,k+72))
if(icos7(k-1).eq.(ip(1)-1)) is3=is3+1
enddo
! hard sync sum - max is 21
nsync=is1+is2+is3
if(nsync .le. 6) then ! bail out
nbadcrc=1
return
endif
j=0
do k=1,NN
if(k.le.7) cycle
if(k.ge.37 .and. k.le.43) cycle
if(k.gt.72) cycle
j=j+1
s1(0:7,j)=s2(0:7,k)
enddo
call indexx(s1sort,8*ND,indxs1)
xmeds1=s1sort(indxs1(nint(0.5*8*ND)))
s1=s1/xmeds1
do j=1,ND
i4=3*j-2
i2=3*j-1
i1=3*j
! Max amplitude
ps=s1(0:7,j)
r1=max(ps(1),ps(3),ps(5),ps(7))-max(ps(0),ps(2),ps(4),ps(6))
r2=max(ps(2),ps(3),ps(6),ps(7))-max(ps(0),ps(1),ps(4),ps(5))
r4=max(ps(4),ps(5),ps(6),ps(7))-max(ps(0),ps(1),ps(2),ps(3))
bmeta(i4)=r4
bmeta(i2)=r2
bmeta(i1)=r1
bmetap(i4)=r4
bmetap(i2)=r2
bmetap(i1)=r1
! Max log metric
psl=log(ps)
r1=max(psl(1),psl(3),psl(5),psl(7))-max(psl(0),psl(2),psl(4),psl(6))
r2=max(psl(2),psl(3),psl(6),psl(7))-max(psl(0),psl(1),psl(4),psl(5))
r4=max(psl(4),psl(5),psl(6),psl(7))-max(psl(0),psl(1),psl(2),psl(3))
bmetb(i4)=r4
bmetb(i2)=r2
bmetb(i1)=r1
! Metric for Cauchy noise
! r1=log(ps(1)**3+ps(3)**3+ps(5)**3+ps(7)**3)- &
! log(ps(0)**3+ps(2)**3+ps(4)**3+ps(6)**3)
! r2=log(ps(2)**3+ps(3)**3+ps(6)**3+ps(7)**3)- &
! log(ps(0)**3+ps(1)**3+ps(4)**3+ps(5)**3)
! r4=log(ps(4)**3+ps(5)**3+ps(6)**3+ps(7)**3)- &
! log(ps(0)**3+ps(1)**3+ps(2)**3+ps(3)**3)
! Metric for AWGN, no fading
! bscale=2.5
! b0=bessi0(bscale*ps(0))
! b1=bessi0(bscale*ps(1))
! b2=bessi0(bscale*ps(2))
! b3=bessi0(bscale*ps(3))
! b4=bessi0(bscale*ps(4))
! b5=bessi0(bscale*ps(5))
! b6=bessi0(bscale*ps(6))
! b7=bessi0(bscale*ps(7))
! r1=log(b1+b3+b5+b7)-log(b0+b2+b4+b6)
! r2=log(b2+b3+b6+b7)-log(b0+b1+b4+b5)
! r4=log(b4+b5+b6+b7)-log(b0+b1+b2+b3)
if(nQSOProgress .eq. 0 .or. nQSOProgress .eq. 5) then
! When bits 88:115 are set as ap bits, bit 115 lives in symbol 39 along
! with no-ap bits 116 and 117. Take care of metrics for bits 116 and 117.
if(j.eq.39) then ! take care of bits that live in symbol 39
if(apsym(28).lt.0) then
bmetap(i2)=max(ps(2),ps(3))-max(ps(0),ps(1))
bmetap(i1)=max(ps(1),ps(3))-max(ps(0),ps(2))
else
bmetap(i2)=max(ps(6),ps(7))-max(ps(4),ps(5))
bmetap(i1)=max(ps(5),ps(7))-max(ps(4),ps(6))
endif
endif
endif
! When bits 116:143 are set as ap bits, bit 115 lives in symbol 39 along
! with ap bits 116 and 117. Take care of metric for bit 115.
! if(j.eq.39) then ! take care of bit 115
! iii=2*(apsym(29)+1)/2 + (apsym(30)+1)/2 ! known values of bits 116 & 117
! if(iii.eq.0) bmetap(i4)=ps(4)-ps(0)
! if(iii.eq.1) bmetap(i4)=ps(5)-ps(1)
! if(iii.eq.2) bmetap(i4)=ps(6)-ps(2)
! if(iii.eq.3) bmetap(i4)=ps(7)-ps(3)
! endif
! bit 144 lives in symbol 48 and will be 1 if it is set as an ap bit.
! take care of metrics for bits 142 and 143
if(j.eq.48) then ! bit 144 is always 1
bmetap(i4)=max(ps(5),ps(7))-max(ps(1),ps(3))
bmetap(i2)=max(ps(3),ps(7))-max(ps(1),ps(5))
endif
! bit 154 lives in symbol 52 and will be 0 if it is set as an ap bit
! take care of metrics for bits 155 and 156
if(j.eq.52) then ! bit 154 will be 0 if it is set as an ap bit.
bmetap(i2)=max(ps(2),ps(3))-max(ps(0),ps(1))
bmetap(i1)=max(ps(1),ps(3))-max(ps(0),ps(2))
endif
enddo
call normalizebmet(bmeta,3*ND)
call normalizebmet(bmetb,3*ND)
call normalizebmet(bmetap,3*ND)
scalefac=2.83
llr0=scalefac*bmeta
llr1=scalefac*bmetb
llra=scalefac*bmetap ! llr's for use with ap
apmag=scalefac*(maxval(abs(bmetap))*1.01)
! pass #
!------------------------------
! 1 regular decoding
! 2 erase 24
! 3 erase 48
! 4 ap pass 1
! 5 ap pass 2
! 6 ap pass 3
! 7 ap pass 4, etc.
if(lapon) then
npasses=4+nappasses(nQSOProgress)
else
npasses=4
endif
do ipass=1,npasses
llr=llr0
if(ipass.eq.2) llr=llr1
if(ipass.eq.3) llr(1:24)=0.
if(ipass.eq.4) llr(1:48)=0.
if(ipass.le.4) then
apmask=0
llrap=llr
iaptype=0
endif
if(ipass .gt. 4) then
iaptype=naptypes(nQSOProgress,ipass-4)
if(iaptype.ge.3 .and. (abs(f1-nfqso).gt.napwid .and. abs(f1-nftx).gt.napwid) ) cycle
if(iaptype.eq.1 .or. iaptype.eq.2 ) then ! AP,???,???
apmask=0
apmask(88:115)=1 ! first 28 bits are AP
apmask(144)=1 ! not free text
llrap=llr
if(iaptype.eq.1) llrap(88:115)=apmag*mcq
if(iaptype.eq.2) llrap(88:115)=apmag*apsym(1:28)
llrap(116:117)=llra(116:117)
llrap(142:143)=llra(142:143)
llrap(144)=-apmag
endif
if(iaptype.eq.3) then ! mycall, dxcall, ???
apmask=0
apmask(88:115)=1 ! mycall
apmask(116:143)=1 ! hiscall
apmask(144)=1 ! not free text
llrap=llr
llrap(88:143)=apmag*apsym(1:56)
llrap(144)=-apmag
endif
if(iaptype.eq.4 .or. iaptype.eq.5 .or. iaptype.eq.6) then
apmask=0
apmask(88:115)=1 ! mycall
apmask(116:143)=1 ! hiscall
apmask(144:159)=1 ! RRR or 73 or RR73
llrap=llr
llrap(88:143)=apmag*apsym(1:56)
if(iaptype.eq.4) llrap(144:159)=apmag*mrrr
if(iaptype.eq.5) llrap(144:159)=apmag*m73
if(iaptype.eq.6) llrap(144:159)=apmag*mrr73
endif
if(iaptype.eq.7) then ! ???, dxcall, ???
apmask=0
apmask(116:143)=1 ! hiscall
apmask(144)=1 ! not free text
llrap=llr
llrap(115)=llra(115)
llrap(116:143)=apmag*apsym(29:56)
llrap(144)=-apmag
endif
endif
cw=0
call timer('bpd174 ',0)
call bpdecode174(llrap,apmask,max_iterations,decoded,cw,nharderrors, &
niterations)
call timer('bpd174 ',1)
dmin=0.0
if(ndepth.eq.3 .and. nharderrors.lt.0) then
ndeep=3
if(abs(nfqso-f1).le.napwid .or. abs(nftx-f1).le.napwid) then
if((ipass.eq.3 .or. ipass.eq.4) .and. .not.nagain) then
ndeep=3
else
ndeep=4
endif
endif
if(nagain) ndeep=5
call timer('osd174 ',0)
call osd174(llrap,apmask,ndeep,decoded,cw,nharderrors,dmin)
call timer('osd174 ',1)
endif
nbadcrc=1
message=' '
xsnr=-99.0
if(count(cw.eq.0).eq.174) cycle !Reject the all-zero codeword
!### if(any(decoded(73:75).ne.0)) cycle !Reject if any of the 3 extra bits is nonzero
if(nharderrors.ge.0 .and. nharderrors+dmin.lt.60.0 .and. &
.not.(sync.lt.2.0 .and. nharderrors.gt.35) .and. &
.not.(ipass.gt.2 .and. nharderrors.gt.39) .and. &
.not.(ipass.eq.4 .and. nharderrors.gt.30) &
) then
call chkcrc12a(decoded,nbadcrc)
else
nharderrors=-1
cycle
endif
!###
i3bit=4*decoded(73) + 2*decoded(74) + decoded(75)
iFreeText=decoded(57)
! if(nbadcrc.eq.0) write(*,3001) nharderrors,nbadcrc,i3bit
!3001 format('A',3i5)
!###
if(nbadcrc.eq.0) then
call extractmessage174(decoded,message,ncrcflag,recent_calls,nrecent)
call genft8(message,mygrid6,bcontest,i3bit,msgsent,msgbits,itone)
if(i3bit.eq.1 .and. iFreeText.eq.0) message(21:21)='1'
if(i3bit.eq.2 .and. iFreeText.eq.0) message(21:21)='2'
if(lsubtract) call subtractft8(dd0,itone,f1,xdt2)
xsig=0.0
xnoi=0.0
do i=1,79
xsig=xsig+s2(itone(i),i)**2
ios=mod(itone(i)+4,7)
xnoi=xnoi+s2(ios,i)**2
enddo
xsnr=0.001
if(xnoi.gt.0 .and. xnoi.lt.xsig) xsnr=xsig/xnoi-1.0
xsnr=10.0*log10(xsnr)-27.0
xsnr2=db(xsig/xbase - 1.0) - 32.0
! write(52,3052) f1,xdt,xsig,xnoi,xbase,xsnr,xsnr2
!3052 format(7f10.2)
if(.not.nagain) xsnr=xsnr2
if(xsnr .lt. -24.0) xsnr=-24.0
return
endif
enddo
return
end subroutine ft8b
subroutine normalizebmet(bmet,n)
real bmet(n)
bmetav=sum(bmet)/real(n)
bmet2av=sum(bmet*bmet)/real(n)
var=bmet2av-bmetav*bmetav
if( var .gt. 0.0 ) then
bmetsig=sqrt(var)
else
bmetsig=sqrt(bmet2av)
endif
bmet=bmet/bmetsig
return
end subroutine normalizebmet
function bessi0(x)
! From Numerical Recipes
real bessi0,x
double precision p1,p2,p3,p4,p5,p6,p7,q1,q2,q3,q4,q5,q6,q7,q8,q9,y
save p1,p2,p3,p4,p5,p6,p7,q1,q2,q3,q4,q5,q6,q7,q8,q9
data p1,p2,p3,p4,p5,p6,p7/1.0d0,3.5156229d0,3.0899424d0,1.2067492d0, &
0.2659732d0,0.360768d-1,0.45813d-2/
data q1,q2,q3,q4,q5,q6,q7,q8,q9/0.39894228d0,0.1328592d-1, &
0.225319d-2,-0.157565d-2,0.916281d-2,-0.2057706d-1, &
0.2635537d-1,-0.1647633d-1,0.392377d-2/
if (abs(x).lt.3.75) then
y=(x/3.75)**2
bessi0=p1+y*(p2+y*(p3+y*(p4+y*(p5+y*(p6+y*p7)))))
else
ax=abs(x)
y=3.75/ax
bessi0=(exp(ax)/sqrt(ax))*(q1+y*(q2+y*(q3+y*(q4 &
+y*(q5+y*(q6+y*(q7+y*(q8+y*q9))))))))
endif
return
end function bessi0
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_WSJT-X_ v1.8 suppports a number of features designed for use
on the VHF and higher bands. These features now include:
- *FT8*, a mode optimized for weak, fading signals such as those often
encountered with multi-hop sporadic E propagation on 50 MHz.
- *JT4*, a mode particularly useful for EME on the microwave bands
- *JT9* fast modes, useful for scatter propagation on VHF bands
- *QRA64*, a mode for EME using a "`Q-ary Repeat Accumulate`" code,
a low-density parity-check (LDPC) code using a 64-character symbol
alphabet
- *MSK144*, a mode for meteor scatter using a binary LDPC code and
Offset Quadrature Phase-Shift Keying (OQPSK). The resulting waveform
is sometimes called Minimum Shift Keying (MSK).
- *ISCAT*, intended for aircraft scatter and other types of scatter
propagation
- *Echo* mode, for detecting and measuring your own lunar echoes
- *Doppler tracking*, which becomes increasingly important for EME
on bands above 1.2 GHz.
- *Auto-sequencing* of transmitted messages for FT8 and the fast modes
with forward error control
[[VHF_SETUP]]
=== VHF Setup
To activate the VHF-and-up features:
- On the *Settings | General* tab check *Enable VHF/UHF/Microwave
features* and *Single decode*.
- For EME, check *Decode at t = 52 s* to allow for extra path delay on
received signals.
- If you will use automatic Doppler tracking and your radio accepts
frequency-setting commands while transmitting, check *Allow Tx
frequency changes while transmitting*. Transceivers known to permit
such changes include the IC-735, IC-756 Pro II, IC-910-H, FT-847,
TS-590S, TS-590SG, TS-2000 (with Rev 9 or later firmware upgrade),
Flex 1500 and 5000, HPSDR, Anan-10, Anan-100, and KX3. To gain full
benefit of Doppler tracking your radio should allow frequency changes
under CAT control in 1 Hz steps.
NOTE: If your radio does not accept commands to change frequency
while transmitting, Doppler tracking will be approximated with a
single Tx frequency adjustment before a transmission starts, using a
value computed for the middle of the Tx period.
- On the *Radio* tab select *Split Operation* (use either *Rig* or
*Fake It*; you may need to experiment with both options to find one
that works best with your radio).
- On the right side of the main window select *Tab 1* to present the
traditional format for entering and choosing Tx messages.
The main window will reconfigure itself as necessary to display
controls supporting the features of each mode.
- If you are using transverters, set appropriate frequency offsets on
the *Settings | Frequencies* tab. Offset is defined as (transceiver
dial reading) minus (on-the-air frequency). For example, when using a
144 MHz radio at 10368 MHz, *Offset (MHz)* = (144 - 10368) =
-10224.000. If the band is already in the table, you can edit the
offset by double clicking on the offset field itself. Otherwise a new
band can be added by right clicking in the table and selecting
*Insert*.
image::Add_station_info.png[align="center",alt="Station information"]
- On the *View* menu, select *Astronomical data* to display a window
with important information for tracking the Moon and performing
automatic Doppler control. The right-hand portion of the window
becomes visible when you check *Doppler tracking*.
image::Astronomical_data.png[align="center",alt="Astronomical data"]
Three different types of Doppler tracking are provided:
- Select *Full Doppler to DX Grid* if you know your QSO partner's locator
and he/she will not be using any Doppler control.
- Select *Receive only* to enable EME Doppler tracking of your receive
frequency to a specific locator. Your Tx frequency will remain fixed.
- Select *Constant frequency on Moon* to correct for your own one-way
Doppler shift to or from the Moon. If your QSO partner does the same
thing, both stations will have the required Doppler compensation.
Moreover, anyone else using this option will hear both of you
without the need for manual frequency changes.
- See <<ASTRODATA,Astronomical Data>> for details on the quantities
displayed in this window.
=== JT4
JT4 is designed especially for EME on the microwave bands, 2.3 GHz and
above.
- Select *JT4* from the *Mode* menu. The central part of the main
window will look something like this:
image::VHF_controls.png[align="center",alt="VHF Controls"]
- Select the desired *Submode*, which determines the spacing of
transmitted tones. Wider spacings are used on the higher microwave
bands to allow for larger Doppler spreads. For example, submode JT4F
is generally used for EME on the 5.7 and 10 GHz bands.
- For EME QSOs some operators use short-form JT4 messages consisting
of a single tone. To activate automatic generation of these messages,
check the box labeled *Sh*.
- Select *Deep* from the *Decode* menu. You may also choose to
*Enable averaging* over successive transmissions and/or *Enable deep
search* (correlation decoding).
image::decode-menu.png[align="center",alt="Decode Menu"]
The following screen shot shows one transmission from a 10 GHz EME
QSO using submode JT4F.
image::JT4F.png[align="center",alt="JT4F"]
=== JT65
In many ways JT65 operation on VHF and higher bands is similar to HF
usage, but a few important differences should be noted. Typical
VHF/UHF operation involves only a single signal (or perhaps two or
three) in the receiver passband. You may find it best to check
*Single decode* on the *Settings -> General* tab. There will be
little need for *Two pass decoding* on the *Advanced* tab. With VHF
features enabled the JT65 decoder will respond to special message
formats often used for EME: the OOO signal report and two-tone
shorthand messages for RO, RRR, and 73. These messages are always
enabled for reception; they will be automatically generated for
transmission if you check the shorthand message box *Sh*.
Be sure to check *Deep* on the *Decode* menu; you may optionally
include *Enable averaging* and *Deep search*.
The following screen shot shows three transmissions from a 144 MHz EME
QSO using submode JT65B and shorthand messages. Take note of the
colored tick marks on the Wide Graph frequency scale. The green
marker at 1220 Hz indicates the selected QSO frequency (the frequency
of the JT65 Sync tone) and the *F Tol* range. A green tick at 1575 Hz
marks the frequency of the highest JT65 data tone. Orange markers
indicate the frequency of the upper tone of the two-tone signals for
RO, RRR, and 73.
image::JT65B.png[align="center",alt="JT65B"]
=== QRA64
QRA64 is an experimental mode in Version 1.7 of _WSJT-X_. The mode is
designed especially for EME on VHF and higher bands; its operation is
generally similar to JT65. The following screen shot shows an example
of a QRA64C transmission from DL7YC recorded at G3WDG over the EME
path at 24 GHz. Doppler spread on the path was 78 Hz, so although the
signal is reasonably strong its tones are broadened enough to make
them hard to see on the waterfall. The red curve shows that the
decoder has achieved synchronization with a signal at approximately
967 Hz.
image::QRA64.png[align="center",alt="QRA64"]
The QRA64 decoder makes no use of a callsign database. Instead, it
takes advantage of _a priori_ (AP) information such as one's own
callsign and the encoded form of message word `CQ`. In normal usage,
as a QSO progresses the available AP information increases to include
the callsign of the station being worked and perhaps also his/her
4-digit grid locator. The decoder always begins by attempting to
decode the full message using no AP information. If this attempt
fails, additional attempts are made using available AP information to
provide initial hypotheses about the message content. At the end of
each iteration the decoder computes the extrinsic probability of the
most likely value for each of the message's 12 six-bit information
symbols. A decode is declared only when the total probability for all
12 symbols has converged to an unambiguous value very close to 1.
TIP: In _WSJT-X_ Version 1.7 QRA64 is different from JT65 in that the
decoder attempts to find and decode only a single signal in the
receiver passband. If many signals are present you may be able to
decode them by double-clicking on the lowest tone of each one in the
waterfall. A multi-decoder like those for JT65 and JT9 has not
yet been written.
=== ISCAT
ISCAT is a useful mode for signals that are weak but more or less
steady in amplitude over several seconds or longer. Aircraft scatter
at 10 GHz is a good example. ISCAT messages are free-format and may
have any length from 1 to 28 characters. This protocol includes no
error-correction facility.
=== MSK144
Meteor-scatter QSOs can be made any time on the VHF bands at distances
up to about 2100 km (1300 miles). Completing a QSO takes longer in
the evening than in the morning, longer at higher frequencies, and
longer at distances close to the upper limit. But with patience, 100
Watts or more, and a single yagi it can usually be done. The
following screen shot shows two 15-second MSK144 transmissions from
W5ADD during a 50 MHz QSO with K1JT, at a distance of about 1800 km
(1100 mi). The decoded segments have been encircled on the *Fast
Graph* spectral display.
image::MSK144.png[align="center",alt="MSK144"]
Unlike other _WSJT-X_ modes, the MSK144 decoder operates in real time
during the reception sequence. Decoded messages will appear on your
screen almost as soon as you hear them.
To configure _WSJT-X_ for MSK144 operation:
- Select *MSK144* from the *Mode* menu.
- Select *Fast* from the *Decode* menu.
- Set the audio receiving frequency to *Rx 1500 Hz*.
- Set frequency tolerance to *F Tol 100*.
- Set the *T/R* sequence duration to 15 s.
- To match decoding depth to your computer's capability, click
*Monitor* (if it's not already green) to start a receiving sequence.
Observe the percentage figure displayed on the _Receiving_ label in
the Status Bar:
image::Rx_pct_MSK144.png[align="center",alt="MSK144 Percent CPU"]
- The displayed number (here 17%) indicates the fraction of available
time being used for execution of the MSK144 real-time decoder. If
this number is well below 100% you may increase the decoding depth
from *Fast* to *Normal* or *Deep*, and increase *F Tol* from 100 to
200 Hz.
NOTE: Most modern multi-core computers can easily handle the optimum
parameters *Deep* and *F Tol 200*. Older and slower machines may not
be able to keep up at these settings; at the *Fast* and *Normal*
settings there will be a small loss in decoding capability (relative
to *Deep*) for the weakest pings.
- T/R sequences of 15 seconds or less requires selecting your
transmitted messages very quickly. Check *Auto Seq* to have the
computer make the necessary decisions automatically, based on the
messages received.
- For operation at 144 MHz or above you may find it helpful to use
short-format *Sh* messages for Tx3, Tx4, and Tx5. These messages are
20 ms long, compared with 72 ms for full-length MSK144 messages.
Their information content is a 12-bit hash of the two callsigns,
rather than the callsigns themselves, plus a 4-bit numerical report,
acknowledgment (RRR), or sign-off (73). Only the intended recipient
can decode short-messages. They will be displayed with the callsigns
enclosed in <> angle brackets, as in the following model QSO
CQ K1ABC FN42
K1ABC W9XYZ EN37
W9XYZ K1ABC +02
<K1ABC W9XYZ> R+03
<W9XYZ K1ABC> RRR
<K1ABC W9XYZ> 73
NOTE: There is little or no advantage to using MSK144 *Sh*
messages at 50 or 70 MHz. At these frequencies, most pings are long
enough to support standard messages -- which have the advantage of
being readable by anyone listening in.
- A special *Contest Mode* for MSK144 can be activated by checking a
box on the *Settings | Advanced* tab. This mode is configured
especially for VHF contests in which four-character grid locators are
the required exchange. When *Contest Mode* is active, the standard QSO
sequence looks like this:
CQ K1ABC FN42
K1ABC W9XYZ EN37
W9XYZ K1ABC R FN42
K1ABC W9XYZ RRR
W9XYZ K1ABC 73
In contest circumstances K1ABC might choose to call CQ again rather
than sending 73 for his third transmission.
=== Echo Mode
*Echo* mode allows you to make sensitive measurements of your own
lunar echoes even when they are too weak to be heard. Select *Echo*
from the *Mode* menu, aim your antenna at the moon, pick a clear
frequency, and toggle click *Tx Enable*. _WSJT-X_ will then cycle
through the following loop every 6 seconds:
1. Transmit a 1500 Hz fixed tone for 2.3 s
2. Wait about 0.2 s for start of the return echo
3. Record the received signal for 2.3 s
4. Analyze, average, and display the results
5. Repeat from step 1
To make a sequence of echo tests:
- Select *Echo* from the *Mode* menu.
- Check *Doppler tracking* and *Constant frequency on the Moon* on the
Astronomical Data window.
- Be sure that your rig control has been set up for _Split Operation_,
using either *Rig* or *Fake It* on the *Settings | Radio* tab.
- Click *Enable Tx* on the main window to start a sequence of 6-second
cycles.
- _WSJT-X_ calculates and compensates for Doppler shift automatically.
As shown in the screen shot below, when proper Doppler corrections
have been applied your return echo should always appear at the center
of the plot area on the Echo Graph window.
image::echo_144.png[align="center",alt="Echo 144 MHz"]
=== VHF+ Sample Files
Sample recordings typical of QSOs using the VHF/UHF/Microwave modes
and features of _WSJT-X_ are available for
<<DOWNLOAD_SAMPLES,download>>. New users of the VHF-and-up features
are strongly encouraged to practice decoding the signals in these
files.