Homemade Teaching FM Wireless Microphone ----- Q5337 FM Transmitter

The wireless faster microphone made by the author is composed of Q5337 as the core, plus one-stage low frequency amplification and radio frequency power amplifying circuit, etc. (can improve the sensitivity of the microphone and RF transmit power). The FM microphone is used as classroom teaching in the big classroom of 250m2 in our unit, has been used for 6 years, the effect is very good. The microphone is high, mainly taken several measures: The signals of the MIC are first sent to the BG1 tube to enlarge, where R1 and C1 are additional treble pre-load circuits. C2 and C3 are the input and output coupling capacitance of the BG1 tube, and its value is used, and it is for attenuating bass, enhances the medium tone. The circuit of the diode D3, D4 and C4, R7 in which the BG1 tube output is reversed is, and the characteristic of the diode is smaller when the diode is positively turned on, and the signal is not affected by the signal of the strong signal, and the signal of the normal intensity is not affected. The rumouts caused by the positive feedback between the conversation and speakers also have a good inhibitory effect. After the microphone signal is amplified by the BG1, the high frequency signal is modulated by the L5 to the interior of the IC, and the high frequency signal is modulated to obtain a large frequencies. C7, C8 and C9, L1 form a frequency modulated signal tuning circuit, which operate between 88 MHz to 108 MHz. The IC's foot-output high-frequency signal is re-coupled to the BG2 tube to perform radio frequency amplification (BG2 can be used in general ultra-high frequency tube) by L2 and C10 tuning. The whole machine is mounted in the housing of a pocket semiconductor radio. The MIC is taken out with a single 80 cm long single-core shielded cord, and this microphone leads megadownload megadownload. The high-frequency signal inductance L4 output from C13 is isolated, and the outer layer of the shield line is received. The MIC is mounted in a suitable latex tube and is fixed with the latex tube with a tie. When using the microphone near the clothes, the machine is hanging on the belt, making the microphone line, and its emission effect is best. L1, L2, L3 with 0.5 mm thick enamel wire around 5 mm round rod, and there is a tap on L2. L4, L5 and L6 can be inductively inductive in general small color code. When debugging, the tightness of L1 is first, so that the radio can receive the signal transmitted by the FM channel, and then the C16 makes the signal stronger. Finally, the radio antenna is shortened, and the emission distance is farthest. If there is a simple field, it can be adjusted to the best effect. This frequency is stable, and it will not drift after a month after adjustment. When I use 4.5V power, the transmit-receive distance is free of directness, with the FM radio listens, it is like a FM radio station.