Metzler Radio signal forwarding - radio converter for existing bell systems - wireless bell set (MT3.0 - built-in and battery transmitter, socket receiver) : Amazon.co.uk: DIY & Tools
AN/ARC-5 - Wikipedia
M9 Bluetooth 5.1 Transmitter Receiver Adapter FM Radio 4-in-1 NFC Audio Adapter Converter Support U Disk / TF Card Playback and Transmit - Snatcher
Arduino Based FM Radio (Receiver) using RDA5807
Single Transistor FM Transmitter circuit
Making a radio transmitter from an old radio - YouTube