Phil writes:
Very interesting. Have you seen the extremely slow CW
program called "Argo"? Written by Italian hams and may
be of interest to you. I have it if you can't find it
(very unlikely.)

No I haven't seen it, but I don't think you can really use CW for this
to full effectiveness even if you've got a 1 hz analog bandpass
filter, because it's hard to decorrelate a signal that slow with all
kinds of intereference. I'd have thought you'd need spread spectrum.
But I'm really not up on this kind of thing.