The device is a miniature radio transmitter operating in the FM band from 88 to 108 MHz. The circuit is implemented using a single transistor that amplifies and modulates the signal from an electret microphone and directly transmits it over the air.
The operating frequency is determined by coil L1 and can be smoothly adjusted by mechanically compressing or expanding the coil turns. The radio microphone is powered by a single 1.5 V battery, making it suitable for compact and portable applications.
A wire with a length of approximately 50 cm is used as the antenna. The operating range between the radio microphone and the radio receiver is approximately 50 to 200 meters and depends on terrain, propagation conditions, and the receiver used.

Technical Specifications:
Frequency range: 88-108 MHz (FM).
Modulation type: FM.
Active component: 1 transistor.
Microphone: electret.
Supply voltage: 1.5 V DC.
Antenna: wire approx. 50 cm.
Operating range: approx. 50-200 m (depending on conditions).
PCB dimensions: 26 x 16 mm.

This product is a DIY assembly kit.