88-108mhz FM transmitter circuit production PCB

  
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C4, L form a resonator: resonant frequency is the FM transmitting power of the microphone, according to the parameters of the diagram component transmission frequency can be between 88 ~ 108MHZ, just FM radio receiver covering the frequency by adjusting the value of L (La stretch or compress the coil L) can easily change the firing frequency, t
88-108mhz FM transmitter circuit production PCB - schematic

o avoid the FM radio. C4 coupled to transmit signals through the antenna to launch out. 6) The resistance of R3 for the MIC to provide a DC bias, R3 of the resistance the greater the sensitivity of the sound collecting microphone weaker, the higher the resistance the smaller the sensitivity of the microphone. 8) circuits in the two diodes D1 and D2 reverse parallel, mainly from a two-way limiter functions, the diode turn-on voltage is only 0. 7V, if the signal voltage exceeds 0. 7V diode conduction will be streaming, so you can ensure that the voices of the signal amplitude can be limited to between plus or minus 0. 7V, the signal will sound too strong too modulation transistor, resulting in sound distortion can not even work properly. 9) CK is an external signal output socket, you can carry-TV headphone jack or headphone jack to listen to such external audio signal source through a dedicated connection line of the introduction of FM transmitter, external sound signal attenuation through R1 and D1, D2, after clipping sent to transistor base to frequency modulation. 10) circuit in the light-emitting diode D3 to indicate the working state, when the FM microphone was electrical work and would light up, R6 is a light-emitting diode current-limiting resistor. C8, C9 is the power supply filter capacitor, because the big capacitor winding fabrication commonly used, so the relatively large equivalent inductance, shunt capacitor C8...



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