Wheeew ... I played with sending FM Radio with RDS with an unmodified Raspberry
Pi. (Use GPIO pin to modulate a signal)
You have many, many harmonics, but it works basically.
Now somebody had even more sparetime on their hands: https://github.com/F5OEO/rpitx
rpitx is a radio transmitter for Raspberry Pi (B,B+ and PI2) which output directly to GPIO.
rpitx is the main software to transmit. It allows to transmit - from IQ files .iq (could be generated by external software like gnuradio or by some few examples of modulations). - from *Frequency/Time** files *.ft (generally used implement easily digital modes)
pissb convert an audio file (Wav 48KHZ mono only!) to SSB (USB right now) and output it on a IQ file.
Have not tried it ... but insane that it can be done ...
* Origin: I'm usually awake near the end of the day (432:1/105)