Talbot Andrew wrote:

[snip]    Just as an example of a visual code,  7 frequency levels, using
two sucessive symbols per character gives potential for 49 different
symbols, enough for letters numbers and a few punctuation.    There
would be no need to turn off the Tx for any symbol,  as a space could be
coded as a character, thus removing ambiguities with dots and noise
spikes.
[snip]

Just out of curiosity : I was thinking, a few weeks ago, to a signalling scheme
that makes use of 2-out-of-12 tones, with the two tones being sent not
sequentially, but simultaneously. I do realize that this would mean that the
PA must be linear. Is this a though requirement for the present crop of  PAs
around ? How much would this requirement be of obstacle to the adoption
of such a scheme (which could also be FEC corrected...).   TNX

73   Alberto    I2PHD