If we want to develope a new 'code' for a time effecient mHz bandwidth
modulation first thing we should do is to make a list of requirements.
My list would be :

- suitable with non-linear amplifiers :
for sake of efficiency and simplicity of the amplifier

- be able to transmit at least 45 different 'characters' :

- if we want to use non-linear amps we can only transmit one 'tone' at a
time, so each character needs to be transitted a a sequence of 'tones'. The
more 'tones' you use the shorter the sequence per character will be but the
larger the required bandwidth, so we will have to find a compromize between
bandwidth and speed.
eg. 47 characters can be transmitted with 7 tones and 2 sequences per
character (49 posibilities) or as 4 tones and 3 sequences per character (64
posibilities).


An important question is : is it worth to make things that complicated ?
Assume the transmission speed is 60 seconds dotlength. In that case the
time needed to transmit 'CQ ON7YD K' would take :

114 minutes in QRSS
40 minutes in DFCW
30 minutes in '7 tone mode' if we have a space between characters
20 minutes in '7 tone mode' if we have no space between characters
40 minutes in '4 tone mode' if we have a space between characters
30 minutes in '4 tone mode' if we have no space between characters

From the above is clear the step from QRSS to DFCW is significant (time

reduced to 35%), but the difference between DFCW and the 'multi tone modes'
is between nil and 50%, so we should have to go to a rather complicated
system (7 tones, no spacing) to have a significant gain.

Other opinions please ...

73, Rik  ON7YD