I am aware that the Raspberry Pi 1, 2,3 can transmit Radio waves on GPIO  pin 4 and 18. There are even special skins that filter the output.

 

"

Previously we posted about the Raspberry Pi’s ability to modulate one of its pins to produce FM transmissions with PiFM. A developer (F5OEO) has recently expanded on this idea, and now the Raspberry Pi is capable of modulating and transmitting FM, AM, SSB, SSTV and FSQ signals anywhere between 130 kHz to 750 MHz.

To transmit with the Raspberry Pi all you need to do is plug in a wire antenna to Pin 12 (GPIO 18) on the GPIO port and run the PiTx software by piping in an audio file or image for SSTV. "

 

 

Would this work on the Orange Pi running Armbian or is there a technical difference between the GPIO pins etc.

20 minutes ago, Seasalt said:

Would this work on the Orange Pi running Armbian or is there a technical difference between the GPIO pins etc.

This is currently possible only on Raspberry Pi boards since it uses SoC hardware features that are not present on other popular SoCs: http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter