Author here.

This code no longer works on new Pi's (it does a lot of low level very hardware stuff from userspace without a proper kernel driver). The code was written in a 24 hour Hackathon, so is very far from maintainable.

However there are other projects to do the same which do work on new Pi's.

There are ways to do a full software defined radio from a pi by using the I2S hardware, and that can transmit GPS, 433 MHz garage door openers, and various other things.

Obviously whatever you transmit you better be using some filters on the output if you want it to be vaguely legal.

https://github.com/F5OEO/rpitx

And it does work with nearly every RPi.

And unlike only doing FM (97MHz-108MHz), it can emit from an IQ datastream from 10KHz to 1.5GHz.