[liberationtech] Efficient digital one-way communication

[Jens Christian Hillerup]

Hi,

One thing I've been thinking a lot about recently is how to make
digital one-way communication feasible for activists, sort of sending
digital information to the broad public. I believe that FM is a good
medium for this because the transmitters are cheap and everybody has a
radio. Hook up the radio to your sound card, and demodulate the audio
back into data, and there you go.

I did a quick hack back in September, called modulera [1]. The idea is
to exploit how pentatonic polyphony always sounds good, regardless of
the notes picked (as long as they're within the scale). The way it
works is that it takes three octaves of some pentatonic scale (in this
case F# major), and silence. This gives 16 different notes. Split up a
byte into two nibbles and you get your two tones. I realize this
approach has a way too low bitrate, but I like the aesthetic in having
the modulated data also be easy on the ears. For any real use, this
would likely need to be scrapped to increase bitrate. Feel free to try
the script, though! I've included the output of the script modulating
itself.

I basically just wanted to throw it out here. Does anybody have
experience in modulating data? Has this kind of digital one-way
communication been done in an activist setting before? Does it make
sense to kick off a project aimed at creating a easily usable system
capable of modulating and demodulating data at modest bitrates
(>15KB/s)?

JC

[1] https://github.com/jchillerup/modulera