The FM microphone direct way , the center frequency of 90MHz, transmit power of about 0.5W, the maximum frequency deviation ± 50kHz, launching no less than 50 meters away . Circuit block diagram The block diagram and schematic diagram shown in Figure 1,2 . Electret microphone audio signal generated by acting on the modulator as T1 's emitter voltage. The voltage is directly changing the size of the junction capacitance of the transistor emitter , junction capacitance circuit parameters as part of its fo about 45MHz or so , after doubling the output frequency up to 90MHz or so , the FM signal amplified by the high-frequency amplifier , Out by the antennas .Modulated signal from the microphone M (CRZ-22) by C1 coupled to the base of the modulator , R1 for the M microphone load resistor .
Modulator from the T1, R2, R3, C2, C3, C4, C6 and L1 composition of common base power Capacity three-point oscillator circuit . As the base of the circuit connected with C2, the high frequency is the base grounded, the audio is grounded collector ( collector received by the L1 power ), collector junction capacitance Cc in parallel in fact ends of the oscillation circuit , therefore , with the Audio signal changes , changes in oscillation frequency corresponding to gain FM signal .
Circuit Features 1 . Direct FM modulator method, the frequency of stable and reliable. 2 . With electret condenser microphone . The microphone has a built- FET composed shot with the device , its high sensitivity , wide frequency response , using the microphone audio amplifier can be added from time to increase the appropriate voltage. 3 . Levels are adjusted components , convenient debugging . C3 adjustable to change the frequency of T1 , T2 adjustable to obtain the harmonic frequency of C7 , T3 adjustable C10 for maximum output.