FM Wireless Microphone circuit diagram
The range of frequencies for the FM broadcast band is 90MHz (MHz = Megahertz or 90 million cycles per second). Because the FM microphone has a variable tuned circuit, it can be tuned to a quiet spot on your local FM broadcast band for the best reception. When the small microphone element is struck by sound, it converts the audio to a change in current through resistor R1 (see schematic diagram).
This electrical change is amplified and eventually frequency modulates the transmitter. The transmission range of the FM microphone is approximately 100 feet, depending on the efficiency of the antenna (properly tuned or not) and the quality of the FM radio receiver.
