Wireless microphone transmitter circuit diagram

Wireless microphone transmitter circuit diagram (1)
This wireless FM microphone is simple to build, it has a transmission range of more than 300 meters (open air). Despite its small number of components and a 3V working voltage, it will easily penetrate apartment buildings over three floors. It can be arbitrarily adjusted in the FM band (87-108MHz) and it can be transmitted in any standard FM receiver.

The coil (L1) should be 3 mm diameter, about 5 turns, 0.61 mm copper wire. You can adjust the frequency by simply adjusting the pitch of the coil. The antenna should be half or quarter wavelength (100MHz 150cm or 75cm).

Circuit description: Audio amplifier (T1) is a standard common emitter amplifier. The 47nF capacitor isolates the microphone from the reference voltage of the transistor and only allows AC signal transmission.

The LC resonant circuit adopts T2, the feedback capacitor C5 and the LC parallel circuits L1 and C4. RF power amplifier (T3) for coupling (C6) signals.

Circuit calibration: put the transmitter about 3 meters away from the FM radio. To about 89-90MHz. Separate the L1 coil of the radio propagation winding to adjust to the desired frequency.

Wireless microphone transmitter circuit diagram (two)
The miniature transmitter is a simple single-tube FM wireless microphone circuit, which is characterized by the oscillating coil double as a transmitting antenna, high transmitting efficiency, not easy to run frequency under interference-free state, and suitable for long-time work. The transmitter is only suitable for placing in a fixed place as a wireless microphone, not suitable for handheld use. Otherwise, the oscillation frequency is easily affected by the human body and is unstable. The following is the transmitter circuit:

The circuit is powered by a 1.5V battery and consumes about 2~3mA, so button batteries can be used and the body can be made smaller. Since the loop antenna L1 used for transmission doubles as an oscillating coil, the high-frequency current that resonates synchronously with the oscillation rate flows in the antenna, so it is always in the best transmission state. The transmitting frequency falls in the common FM radio frequency band for easy reception. With a high-sensitivity receiver, the transmitting distance can reach more than one hundred meters (open field).

The production of the built-in loop antenna: The enameled wire with a length of 160mm and a diameter of 1mm is made into a metal ring or box shape and embedded in the case.

Debugging: adjust capacitor C3 so that the transmitting frequency falls within the FM frequency band between 88-108MHz to facilitate reception with FM radio. When debugging, keep your hands away from the transmitting antenna, and don’t put it close to metal objects, so as not to affect the oscillation frequency and transmission distance.

The 3355 UHF tube has a characteristic frequency of 6.5GHz and a power consumption of 600mW. Microphone MIC should use high-sensitivity electret microphone, which can be selected through a multimeter.