DATE: November 25, 2017
The frequency best wireless microphone is about 83MHz, just turn off the turn of the coil L a little, so that the oscillation frequency of 88MHz-108MHz can be, you can with any FM radio to receive the high-frequency signal, and restore from the high-frequency signal A sound signal. Also equipped with an external audio jack and adjustable resistance adjust the amount of attenuation of the input audio signal.
Frequency range: 80MHz-103MHz (according to the circuit diagram parameters, only adjust the coil turns)
Working voltage: 1.5V -9V
Launch radius: more than 100 meters
Test conditions: 4.5V voltage, normal radio receiver, wireless microphone antenna 50cm long thin wire
Test Location: high-rise residential area
MIC first natural sound signal into an audio signal through the C2 coupling to the base of Q modulation, when there is a voice signal, the junction capacitance of the transistor will change → oscillation frequency changes to complete the frequency modulation, that is, frequency modulation. And then coupled to the C8 coupling high-frequency tuning amplifier to modulate the high-frequency signal amplification, and then through the C12 , L3 and TX outward transmission frequency changes with the sound signal of high frequency electromagnetic waves.
Wherein R1 is a wireless microphone MIC bias resistor, typically in the 2K-5.6K selected. R4 is the collector resistance. R5 is the base resistance, providing bias current to Q1 . R6 is the emitter resistance, the role of a stable Q1 DC operating point; Q2 , R7 , R8 , C4 , C5 , L1 , C6 ,C7 composed of high-frequency oscillator circuit, R7 to Q2 base to provide bias current, C5 and L1 oscillation circuit, change its value can change the firing frequency, C4 for the feedback capacitor, R8 Q2 steady DC work point role, C7 DC blocking AC capacitor; Q3 , R9 , R10 , L2 , C10 , C11 composed of high-frequency power amplifier. R9 provides base current to power tube Q3 , C10 and L2 amplify the tuning loop, and the oscillation circuit C5 and L1 get the maximum output power at the same frequency when tuned to the oscillation frequency, with the longest transmitting distance.
We designed the transmit frequency in the FM radio band so that it can be used with any FM radio to receive the high frequency signal and to restore the audible signal from the high frequency signal for a variety of purposes.
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