Circuit diagram of FM transmitter (1)

The working principle and circuit diagram of FM transmitter can meet the requirements of transmitting distance, and can input sound signal with microphone and line at the same time for background dubbing. The circuit also adds a modulation monitoring header, so as to better master and use the transmitter. The circuit is shown in the figure below. After a brief introduction, do you think it has as many functions as a set of broadcasting station equipment. Yes, this small transmitter can help you set up an amateur FM radio station easily! The coverage is about 500m.

Complete circuit diagram of FM transmitter

Circuit principle and component selection:

After the microphone picks up the signal, it is coupled to BG1 and the peripheral circuit to form a voltage negative feedback single transistor amplifier. The weak voltage signal is amplified to enough amplitude, and the amplified line input signal of U1A enters into U1B for mixing. One channel of mixed signal is demodulated by R17, which is composed of BG2 FET and surrounding circuit. The characteristic of LCO is simple, high efficiency and high stability. Good waveform, modulation bandwidth, which is particularly important for amateur FM transmitter. Finally, the amplifier made of BG3 is amplified and transmitted through the transmitting antenna, and the ordinary FM radio can listen to the radio. The other signal is amplified by u1c amplifier and then rectified by D2 simple wave. The micro ammeter is driven by DC to monitor the modulation amplitude of the signal. Generally speaking, the use of the tone system should not exceed 85%. The integrated circuit uses LM324 and other universal four operational amplifiers to form a single power reverse input mode, that is, the positive phase input voltage is set at half of the power supply voltage. The monitor head is 200u type, and 2sc1815 is selected for bg1.bg3. 3do2 FET is used for BG2 and 1s2267 is used for D2 varactor. 1 / 4 wavelength is required for antenna. If rod antenna is used, it is better not to be less than one meter. Otherwise, it will not achieve the effect of overdue launch.

Circuit diagram of FM transmitter (2)

Circuit diagram of classic 15W FM transmitter

Complete circuit diagram of FM transmitter

Circuit diagram of FM transmitter (3)

The wireless microphone circuit design is reasonable, beautiful and generous, long transmission distance, long service life, economical and low power consumption, which is very suitable for receiving and using ordinary FM radio.

Manufacturing of oscillation coil L:On the Φ 5mm straight shank drill flower, use the Φ 0.5mm enameled wire to wind flat for 4t and take off.

Adjustment of oscillation coil L:Turn on the radio (placed in FM section) and microphone switch, and then hold the microphone, while talking to the microphone, adjust the console knob until your own voice is heard from the radio. If you still can’t hear your own voice in the whole frequency band (i.e. 88-108MHz), carefully move the oscillation coil L. when you dial, you only need to open or narrow the distance between each turn of the coil, and you should carefully adjust it. If the adjustment of coil tightness still has no rounding effect, weld l down to increase or decrease one turn (due to the influence of electronic component parameters), and then continue the above adjustment after re welding.

Complete circuit diagram of FM transmitter

Before preparing for installation and production, please use a multimeter to screen the quality of each component. If possible, measure the electric capacity of each ceramic chip capacitor, so that there is no risk and the installation is successful. During welding, the quality shall be guaranteed, and false welding, false welding and wrong welding shall not occur.

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