187 lines
8.0 KiB
Plaintext
187 lines
8.0 KiB
Plaintext
White Paper: FT8 for DXpeditions
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-----------------------------------
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Joe Taylor, K1JT - October 27, 2017
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Assumptions:
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1. WSJT-X will have two distinct options that enable the maximum-rate
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QSO exchanges described below. Fox must select "Fox"; all Hounds must
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select "Hound".
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2. There will be an announced basic dial frequency for each band, say
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f0=14082 kHz for 20m. This is the basic Channel.
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3. Fox always transmits in the 1st sequence, 200-800 Hz above f0.
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4. Hounds call in 2nd sequence, 1000-5000 Hz above f0. Hounds
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transmitting below f0+1000 Hz will not be answered.
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5. If found necessary, additional Channels may be defined in which
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Hounds can transmit. (However, I suggest that CQ-by-call-area may
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be easier to implement and use; and the software could be made to
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prevent Hounds in the wrong area from transmitting.)
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6. Ideally, Fox and Hounds should all use CAT control configured with
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*Split Operation* set to *Rig* or *Fake It*, and transceiver dial
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frequencies should best be calibrated to within a few Hz. (WSJT-X
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provides tools that make this fairly easy to do.)
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When Fox is running a pileup, QSOs will look something like the
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following exchanges. Here I've assumed the Fox callsign is KH1DX,
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his locator AJ10:
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------------------------------------------------------------------------
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Fox Hounds
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------------------------------------------------------------------------
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1. CQ KH1DX AJ10
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2. KH1DX K1ABC FN42, KH1DX W9XYZ EN37, ...
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3. K1ABC KH1DX -13
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4. KH1DX K1ABC R-11
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5. K1ABC RR73; W9XYZ <KH1DX> -17
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6. ... no copy from W9XYZ ...
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7. W9XYZ KH1DX -17
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8. ... no copy from W9XYZ ...
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9. G4AAA KH1DX -11
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10. KH1DX G4AAA R-03
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11. G4AAA RR73; DL3BBB <KH1DX> -12
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12. KH1DX DL3BBB R-09
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13. DL3BBB RR73; DE <KH1DX>
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14. ...
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------------------------------------------------------------------------
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All messages except those containing "<...>" are standard FT8 messages
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(i3bit=0, iFreeText=0). Hounds transmit only standard messages.
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Fox transmits standard messages and also special messages with
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i3bit=1. The special messages contain a callsign whose completed QSO
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is being acknowledged; a callsign for the next station to be worked; a
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hash code corresponding to the Fox callsign; and a signal report.
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Users will see the Fox callsign enclosed in angle brackets, <KH1DX>.
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The 72-bit message payload contains two 28-bit callsigns, a 10-bit
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hash code, and a 6-bit signal report. If no call has been queued up
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by Fox for the next QSO, the acknowledgment message takes the
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abbreviated form shown in line 13 above.
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When a Hound receives a message with i3bit=1, the decoder interprets
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the remaining 72 bits as described above. If the 10-bit hash code
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matches that for Fox's callsign, the message is displayed as in the
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QSO exchanges shown above. Otherwise the message is considered a
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false decode and is not displayed.
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Station Setup and Operation for FOX
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-----------------------------------
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A wide Rx bandwidth (up to 5 kHz) is selected. The basic dial
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frequency is set 1 kHz above f0 (thus 14083 kHz in my example) and the
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audio TxFreq somewhere between -200 and -800 Hz. (Yes, negative
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numbers are OK. *Split Operation* will reset the Tx dial frequency as
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needed and will keep the generated Tx audio frequency between 1500 and
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2000 Hz.) Hounds with audio TxFreq set to N Hz will be received by Fox
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at N-1000 Hz.
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WSJT-X at Fox will maintain and display a list of all decoded Hounds
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calling Fox in the past 2 to 4 Rx cycles. The list might look
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something like this (but typically will be much longer):
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----------------------------
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Call Grid Rpt Freq
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----------------------------
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AA2UK FM29 -11 240
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AD9H EN61 +02 1260
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K0TPP EM48 -15 1980
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N2BJ EN61 +11 540
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N4NDR EL98 -17 4620
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NX4E EM70 +00 3780
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ON3LA JN29 -10 3300
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PD9BG JO21 -21 2100
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PJ4/KA1XYZ FK60 -07 1020
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VE1SKY FN74 +03 1620
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WB2REM EL97 -13 3060
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...
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----------------------------
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Fox can choose to have the list sorted on any column.
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Fox selects a Hound to call next by clicking on a line. Or he can hit
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"F1" to have the program select a caller according to one of these
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criteria (maybe others as well?):
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- Weakest caller
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- Strongest caller
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- Strongest one below -N dB (with N selectable)
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- Choose a call at random
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- Random choice with S/N between snrMin and snrMax dB.
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After a particular Hound has been called, Fox's Auto-Sequencer looks
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for a response containing "R+rpt" originating from that same callsign.
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If such a message is received, Fox's next transmission will be the
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special "acknowledge-and-call-next" type, with i3bit=1. If the
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expected message is not received, as in example line 6 above, the
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report is sent to the same station again. If the second attempt fails
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and another Hound callsign has been queued up, the QSO is aborted and
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the next Hound is called.
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Station Setup and Operation for Hounds
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--------------------------------------
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Dial frequency is set to f0, 14082 kHz in my example. Rx bandwidth and
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displayed range on the Wide Graph can be anything convenient, say 200
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to 2600 Hz. (Signal from Fox will be expected between 200 and 800
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Hz.) Enter callsign and locator of Fox on WSJT-X main window as *DX
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Call* and *DX Grid*. Choose a TxFreq offset of 1000 + 60*N for some N
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in the range 1 to 80 (maybe even higher?). Move TxFreq as desired,
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hoping to find a clear slot, by using Shift+F11 and Shift+F12.
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- Hit F1 to call Fox in your next Tx sequence. Yes, you must hit F1
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repeatedly, in order to keep calling.
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- The Auto-sequencer will watch for a decoded message that contains
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"MyCall DXcall rpt" or "MyCall <DXcall> rpt". When one of these is
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received, your next transmission will be "DXcall MyCall R+rpt",
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sent automatically.
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- After you send the "R+rpt" message, AutoSeq will watch for a
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message that starts with "MyCall RR73; ...". When that is
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received, you're in his log, and you'll be prompted to log the QSO.
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Random thoughts
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---------------
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Fox's decoder has access to signals in a 4 kHz (maybe even 5 kHz?)
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window. At 60 Hz intervals, that's enough for around 65 (or 80?)
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non-overlapping Hound signals. If the pileup becomes too deep, more
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spectrum might be used; but note that WSJT-X can't access more than 5
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kHz at one time. A better solution might be for Fox to call "CQ n
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KH1DX AJ10", where n is a single digit indicating call area. The
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decoder could then limit the list of eligible calls to those in the
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specified call area. After decoding such a CQ, the software at Hound
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could refuse to transmit unless MyCall falls in the specified call
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area. (Other special CQ formats can be imagined that would limit the
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eligible Hound callsigns even further.)
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We haven't thought much, yet, about logging issues for Fox. I imagine
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we could do what's necessary to join a N1MM+ logging network, if that's
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deemed desirable.
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A few questions:
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Q1: Should the Auto-Sequencer allow for other cases in which a QSO has
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been initiated by Fox, but one of next two messages is not copied by
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either Fox or Hound? For example, what if K1ABC does not copy message
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#5? Should he keep sending his message "KH1DX K1ABC R-11" ? If Fox
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receives this message again, should he acknowledge again? And poor
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W9XYZ, who never received an acknowledgment, will probably keep
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sending "KH1DX W9XYZ R-19", or whatever. If Fox eventually copies the
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message, should the program remember that W9XYZ had been called, and
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thus send him an acknowledgment?
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Q2: Should we provide a stack for several to-be-called callsigns,
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rather than just one? Should re-ordering of calls in the stack be
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permitted?
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Q3: Can we handle WSJT-X "Type 1" and "Type 2" compound callsigns, for
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Hounds?
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