White Paper: FT8 for DXpeditions
\n——————————–<\/p>\n
Assumptions:<\/p>\n
1. WSJT-X will have two distinct options that enable the maximum-rate
\nQSO exchanges described below. Fox must select “Fox”; all Hounds must
\nselect “Hound”.<\/p>\n
2. There will be an announced basic dial frequency for each band, say
\nf0=14082 kHz for 20m. This is the basic Channel.<\/p>\n
3. Fox always transmits in the 1st sequence, 200-800 Hz above f0.<\/p>\n
4. Hounds call in 2nd sequence, 1000-5000 Hz above f0. Hounds
\ntransmitting below f0+1000 Hz will not be answered.<\/p>\n
5. If found necessary, additional Channels may be defined in which
\nHounds can transmit. (However, I suggest that CQ-by-call-area may
\nbe easier to implement and use; and the software could be made to
\nprevent Hounds in the wrong area from transmitting.)<\/p>\n
6. Ideally, Fox and Hounds should all use CAT control configured with
\n*Split Operation* set to *Rig* or *Fake It*, and transceiver dial
\nfrequencies should best be calibrated to within a few Hz. (WSJT-X
\nprovides tools that make this fairly easy to do.)<\/p>\n
\nWhen Fox is running a pileup, QSOs will look something like the
\nfollowing exchanges. Here I’ve assumed the Fox callsign is KH1DX,
\nhis locator AJ10:<\/p>\n
————————————————————————
\nFox Hounds
\n————————————————————————
\n1. CQ KH1DX AJ10
\n2. KH1DX K1ABC FN42, KH1DX W9XYZ EN37, …
\n3. K1ABC KH1DX -13
\n4. KH1DX K1ABC R-11
\n5. K1ABC R 73; W9XYZ -17
\n6. … no copy from W9XYZ …
\n7. W9XYZ KH1DX -17
\n8. … no copy from W9XYZ …
\n9. G4AAA KH1DX -11
\n10. KH1DX G4AAA R-03
\n11. G4AAA R 73; DL3BBB -12
\n12. KH1DX DL3BBB R-09
\n13. DL3BBB R 73; DE
\n14. …
\n————————————————————————<\/p>\n
All messages except those containing “” are standard FT8 messages
\n(i3bit=0, iFreeText=0). Hounds transmit only standard messages.<\/p>\n
Fox transmits standard messages and also special messages with
\ni3bit=1. The special messages contain a callsign whose completed QSO
\nis being acknowledged; a callsign for the next station to be worked; a
\nhash code corresponding to the Fox callsign; and a signal report.
\nUsers will see the Fox callsign enclosed in angle brackets, .
\nThe 72-bit message payload contains two 28-bit callsigns, a 10-bit
\nhash code, and a 6-bit signal report. If no call has been queued up
\nby Fox for the next QSO, the acknowledgment message takes the
\nabbreviated form shown in line 13 above.<\/p>\n
When a Hound receives a message with i3bit=1, the decoder interprets
\nthe remaining 72 bits as described above. If the 10-bit hash code
\nmatches that for Fox’s callsign, the message is displayed as in the
\nQSO exchanges shown above. Otherwise the message is considered a
\nfalse decode and is not displayed.<\/p>\n
\nStation Setup and Operation for FOX
\n———————————–<\/p>\n
A wide Rx bandwidth (up to 5 kHz) is selected. The basic dial
\nfrequency is set 1 kHz above f0 (thus 14083 kHz in my example) and the
\naudio TxFreq somewhere between -200 and -800 Hz. (Yes, negative
\nnumbers are OK. *Split Operation* will reset the Tx dial frequency as
\nneeded and will keep the generated Tx audio frequency between 1500 and
\n2000 Hz.) Hounds with audio TxFreq set to N Hz will be received by Fox
\nat N-1000 Hz.<\/p>\n
WSJT-X at Fox will maintain and display a list of all decoded Hounds
\ncalling Fox in the past 2 to 4 Rx cycles. The list might look
\nsomething like this (but typically will be much longer):<\/p>\n
—————————-
\nCall Grid Rpt Freq
\n—————————-
\nAA2UK FM29 -11 240
\nAD9H EN61 +02 1260
\nK0TPP EM48 -15 1980
\nN2BJ EN61 +11 540
\nN4NDR EL98 -17 4620
\nNX4E EM70 +00 3780
\nON3LA JN29 -10 3300
\nPD9BG JO21 -21 2100
\nPJ4\/KA1XYZ FK60 -07 1020
\nVE1SKY FN74 +03 1620
\nWB2REM EL97 -13 3060
\n…
\n—————————-<\/p>\n
Fox can choose to have the list sorted on any column.<\/p>\n
Fox select a Hound to call next by clicking on a line. Or he can hit
\n“F1” to have the program select a caller according to one of these
\ncriteria (maybe others as well?):<\/p>\n
– Weakest caller
\n– Strongest caller
\n– Strongest one below -N dB (with N selectable)
\n– Choose a call at random
\n– Random choice with S\/N between snrMin and snrMax dB.<\/p>\n
After a particular Hound has been called, Fox’s Auto-Sequencer looks
\nfor a response containing “R+rpt” originating from that same callsign.
\nIf such a message is received, Fox’s next transmission will be the
\nspecial “acknowledge-and-call-next” type, with i3bit=1. If the
\nexpected message is not received, as in example line 6 above, the
\nreport is sent to the same station again. If the second attempt fails
\nand another Hound callsign has been queued up, the QSO is aborted and
\nthe next Hound is called.<\/p>\n
\nStation Setup and Operation for Hounds
\n————————————–<\/p>\n
Dial frequency is set to f0, 14082 kHz in my example. Rx bandwidth and
\ndisplayed range on the Wide Graph can be anything convenient, say 200
\nto 2600 Hz. (Signal from Fox will be expected between 200 and 800
\nHz.) Enter callsign and locator of Fox on WSJT-X main window as *DX
\nCall* and *DX Grid*. Choose a TxFreq offset of 1000 + 60*N for some N
\nin the range 1 to 80 (maybe even higher?). Move TxFreq as desired,
\nhoping to find a clear slot, by using Shift+F11 and Shift+F12.<\/p>\n
– Hit F1 to call Fox in your next Tx sequence. Yes, you must hit F1
\nrepeatedly, in order to keep calling.<\/p>\n
– The Auto-sequencer will watch for a decoded message that contains
\n“MyCall DXcall rpt” or “MyCall rpt”. When one of these is
\nreceived, your next transmission will be “DXcall MyCall R+rpt”,
\nsent automatically.<\/p>\n
– After you send the “R+rpt” message, AutoSeq will watch for a
\nmessage that starts with “MyCall R 73; …”. When that is
\nreceived, you’re in his log, and you’ll be prompted to log the QSO.<\/p>\n
Random thoughts
\n—————<\/p>\n
Fox’s decoder has access to signals in a 4 kHz (maybe even 5 kHz?)
\nwindow. At 60 Hz intervals, that’s enough for around 65 (or 80?)
\nnon-overlapping Hound signals. If the pileup becomes too deep, more
\nspectrum might be used; but note that WSJT-X can’t access more than 5
\nkHz at one time. A better solution might be for Fox to call “CQ n
\nKH1DX AJ10″, where n is a single digit indicating call area. The
\ndecoder could then limit the list of eligible calls to those in the
\nspecified call area. After decoding such a CQ, the software at Hound
\ncould refuse to transmit unless MyCall falls in the specified call
\narea. (Other special CQ formats can be imagined that would limit the
\neligible Hound callsigns even further.)<\/p>\n
We haven’t thought much, yet, about logging issues for Fox. I imagine
\nwe could do what’s necessary to join a N1MM+ logging network, if that’s
\ndeemed desirable.<\/p>\n
A few questions:<\/p>\n
Q1: Should the Auto-Sequencer allow for other cases in which a QSO has
\nbeen initiated by Fox, but one of next two messages is not copied by
\neither Fox or Hound? For example, what if K1ABC does not copy message
\n#5? Should he keep sending his message “KH1DX K1ABC R-11” ? If Fox
\nreceives this message again, should he acknowledge again? And poor
\nW9XYZ, who never received an acknowledgment, will probably keep
\nsending “KH1DX W9XYZ R-19”, or whatever. If Fox eventually copies the
\nmessage, should the program remember that W9XYZ had been called, and
\nthus send him an acknowledgment?<\/p>\n
Q2: Should we provide a stack for several to-be-called callsigns,
\nrather than just one? Should re-ordering of calls in the stack be
\npermitted?<\/p>\n
Q3: Can we handle WSJT-X “Type 1” and “Type 2” compound callsigns, for
\nHounds?<\/p>\n","protected":false},"excerpt":{"rendered":"
White Paper: FT8 for DXpeditions ——————————– … <\/p>\n