Hi Richard,

Thanks for your comments and suggestions.

On 2/9/2018 5:10 AM, Richard Lamont G4DYA wrote:
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.

Of course one can imagine many possible alternatives to the signaling scheme we chose for Fox. For sure, there are more ways than one to skin this cat.

Your idea of a signal with ~2500 Hz bandwidth would require entirely new schemes for coding and modulation, and their inverses -- probably requiring some months of software design, coding, and testing. In contrast, the approach we have taken needed only relatively minor additions to the well-tested tools of standard FT8. Our scheme has the advantage of trivial scaling, up and down, as N changes. When band conditions are poor, Fox can set N=1 and concentrate full power into a single signal.

Oh yes... it seems to me that your 2500 Hz bandwidth would likely not be permissible in some jurisdictions, at least in the band segments we are now using?

Anyway... I do appreciate your thoughtful input. We certainly do not claim that FT8 DXpedition Mode is, once and for all, the best conceivable design for its intended purpose.

        -- 73, Joe, K1JT

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