With this simple radio microphone, you can transmit sound from the microphone to a distance of 100-150 meters and receive a signal to a radio receiver with an FM band.This class of transmitters is also called radio bugs, but it should be borne in mind that they cannot be used illegally.Such a transmitter according to the same scheme is sold on Aliexpress.The circuit is simple, soldered and works immediately and does not require special configuration.
A generator is actually assembled on a transistor 2sc9018 or c9018, which in my case outputs a signal with a frequency of about 85 MHz.This signal is modulated by sound using an electret microphone.The antenna is a 50-70 cm long wire.With the help of the C2 capacitor, you can choose the optimal mode of operation of the transmitter, its capacity ranges from 10 to 20 pF.With the help of an inductor or a capacitor C1, the frequency of radiation can be changed.But you can do this by shifting and pushing the coils onto the coil.
The coil is wound on a frame with a diameter of 5 mm and contains 4 turns of copper wire with a diameter of approximately 0.6-0.7 mm.
The range of the transmitter in an open area was about 100 meters, this is a confident reception.Up to 150 meters will be an uncertain reception.
