Some years ago I proposed GPS / UTC seconds locked coherent signalling
on LF, but didn't have the expertise to write the software - and
certainly not to implement strong FEC !
Somewhere around February, 2004, Bill de Carle, VE2IQ, came out with a
version of AFRICAM that implemented GPS-synched BPSK. A number of us
played with it in the 160-190 kHz U.S. "Lowfer" band. The GPS sync
greatly reduced the lock-in time at the decoder end, and was quite
effective. When the first of the U.S. experimental stations arrived on
2200 meters later that year, we tried it down there, again with good
results among a small group of listeners. Given the small target
audience, we all moved on other things.
Anyway, just to note for historical purposes that some of this has been