Just get an FM receiver, connect a 20 - 40 cm plain wire to the Raspberry Pi's GPIO4 (PIN 7 on GPIO header) to act as an antenna, and you are ready for broadcasting.
This project uses the general clock output to produce frequency modulated radio communication. It is based on an idea originally presented by [Oliver Mattos and Oskar Weigl](http://icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter) at [PiFM project](http://icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter).
On Raspberry Pi 4 other built-in hardware probably interfers somehow with this software making transmitting not possible on all standard FM broadcasting frequencies. In this case it is recommended to:
1. Compile executable with option to use GPIO21 instead of GPIO4 (PIN 40 on GPIO header):
2. Changing either ARM core frequency scaling governor settings to "powersave" or changing ARM minimum and maximum core frequencies to one constant value (see: https://www.raspberrypi.org/forums/viewtopic.php?t=152692 ).
[hydranix](https://github.com/markondej/fm_transmitter/issues/144) has came up with simple method of using transmitter as an general audio output device. In order to achieve this you should load "snd-aloop" module and stream output from loopback device to transmitter application:
Please keep in mind loopback device should be set default ALSA device (see [this article](https://www.alsa-project.org/wiki/Setting_the_default_device)). Also parameter "-D hw:X,1,0" should be pointing this device (use card number instead of "X").
### Microphone support
In order to use a microphone live input use the `arecord` command, eg.:
Included sample audio was created by [graham_makes](https://freesound.org/people/graham_makes/sounds/449409/) and published on [freesound.org](https://freesound.org/)