As a start John, we might have to define our terms as to what is acceptable as "speech transmission"!

Dependant upon the defined term we can commence with a series of logical steps toward such a goal.

At the "starter" end there is perhaps the simple "Voice-to-code, Code-to-voice" protocol of speech recognition to keyer (morse or other) and the various demod possibilities with the attendant condition that one might call "CQ" into one's mic. today, and be attendant upon one's receiving apparatus for a speech reply sometime during the following week! The thing starts to take on interesting possibilities if it is acceptable to involve networking infrastructure with only some of the task being allocated to the RF path at LF.

However, I believe that chucking these questions and ideas up in the air for all to catch and play with is what will prompt experimentation and potential solution(s).

"Is there somebody out there ?" is a whole sentence and, as we are all aware, requires very few data bits to be identified as such in innumerable languages without complicated translation.

Lateral thinking might, therefore, suggest that "speech" should be redefined when "transmission" at narrow bandwidths is invoked. This is more or less what we are doing today - conveying sense and meaning. Your question may in fact be posing as a whole range of problems to whet our appetites!

 

Pat g4gvw