On 02/02/18 17:53, Joe Taylor wrote:

> You have probably heard something about recent efforts to develop a
> special "FT8 DXpedition Mode" in WSJT-X.  This message aims to bring you
> up-to-date on our progress, and generally to make our plans more widely
> known.

Hi Joe. Thanks for this.

For the sake of brevity and clarity, I'll refer to traditional symmetric
FT8 as FT8S and the proposed DXpedition mode as FT8D.

It seems to me that you're missing a trick. Given that FT8D is not
backwards-compatible with WSJT-X 1.8.0 or earlier, there's no need to
make FT8D decodable on FT8S systems. Indeed there's an advantage in
making it incompatible, as it will prevent people using old versions and
getting frustrated when it doesn't work.

So there's no need for the Fox to transmit FT8S-type signals using
multiple tones. It would be possible to use a new modulation scheme, for
the Fox only, which uses the whole of the SSB channel and not waste the
bandwidth above 900 Hz.

This would enable the Fox to transmit a much larger payload, rather than
N payloads of 75 bits each, of which N x 28 are the Fox's own callsign.
The multiplexing of the signals to each hound would be done (somehow)
within the single payload, rather than by FDM.

Richard G4DYA

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