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The production circuit of three-tube FM wireless microphone

2014-11-20 16:11  
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The production circuit of three-tube FM wireless microphone
The production circuit of three-tube FM wireless microphone
The production circuit of three-tube FM wireless microphone
The microphone uses the direct FM mode with the center frequency in 90MHz, transmit power is about 0.5W, and the largest frequency offset is 50kHz, and the transmitting distance is not less than 50 meters. The block diagram and schematic diagram are shown in Figure 1,2. The audio signal generated by the electret microphone acts on the emission junction of the modulator T1 as the modulation voltage. The size of voltage directly changes the junction capacitance of the transistor emitter junction, and the junction capacitance is a part of the circuit parameters; fo is about 45MHz, and the output frequency can be up to 90MHz after frequency doubling, the FM signal is emitted by an antenna after being amplified by high-frequency amplifier.