This video depicts the successful transmission of AFSK data via a radio link between two Linux machines using a R-Pi and an RTL-SDR dongle. The crew at Kprod posted this cool RTL-SDR project on their blog. They use minimodem to do the encoding in a FLAC or in a WAV format, then use the R-Pi as a transmitter. The RTL-SDR is setup to receive the signal and send the audio to minimodem for decoding.