Reading "Coak and Dagger: More Cuban Spy Broadcasts" in the July issue of Popular Communications, writer Steven Handler mentioned that Cuban spy stations transmit data using "Redundant Digital File Transfer (RDFT), a digital mode developed for amateur radio operators."
I need to get out more because I was not familiar with RDFT. In fact, I had never heard of it.
A little Googling and I discovered that RDFT was the first digital modulation signal format for digital SSTV and was the brain child of Barry Sanderson, KB9VAK. I plead ignorance because SSTV is one of the few ham radio modes I have not tried. (After all, who wants to see my mug? I might get an FCC citation for scaring the kids.)
Chapter 9 of Image Communications on Short Waves also known as the "SSTV Handbook," a freely downloadable e-book by Martin Bruchanov, OK2MNM, covers RDFT.
There is also a YouTube video of a recording of a Cuban numbers station using RDFT on July 24, 2011, on 9063 kHz in the AM mode.
Beyond RDFT, Rick Muething, KN6KB, proffered SCAMP (Sound Card Amateur Message Protocol) at the 2004 Digital Communications Conference (DCC). "SCAMP leverages the work by Barry Sanderson, KB9VAK and employs an ARQ 'wrapper' around Barry's Redundant Digital File Transfer (RDFT) scheme to provide the error-free automatic operation necessary for today's modern digital message systems.
Until next time, keep on surfin'!