> Please note that due of the hardware of the raspberry pi, harmonics ARE generated on 3x, 5x, 7x and 9x the desired frequency. Those harmonics are polluting important services like emergency services a d others.
Please do not use the GPIO of a Raspberry Pi to generate a high frequency to emit radio waves. Putting square waves on the air is always asking for trouble. A simple filter is not a proper solution if the source is so dirty.
For a project as well built of this seems, it seems odd that they would advice people to use such a hacky way. Syncing networked clients to play audio at exactly the same time is a solved problem.
The project also cursorily mentions the need to use a bandpass filter to avoid interference but fails to explain the specific device needed or how to wire it up in the instructions.
[EDIT] I debated whether or not to say it but I will: this is just irresponsible. There is no way to legally use this project as is. The user would have to have additional knowledge of RF hardware and regulations to make it compliant.