Production of three tube frequency modulation wireless microphones, FM Transmitter
Keywords: three-tube FM wireless microphone production
The microphone adopts direct frequency modulation mode, the center frequency is 90MHz, the transmit power is about 0.5W, the maximum frequency butters 50 kHz, the emission distance is not less than 50 meters. Circuit block diagram
The block diagram and schematic diagram are shown in Figures 1, 2. The audio signal generated by the electret microphone acts as the emission junction of the modulator T1 as the modulation voltage. The magnitude of the voltage directly changes the junction capacitance of the transistor emission junction, and the tubular capacitance is part of the loop parameter, and its FO is about 45 MHz, and the frequency modulation frequency is increased to 90 MHz, and the frequency modulation signal is released after high frequency. The antenna is emitted out. The circuit principle modulation signal is coupled to the base of the microphone M (CRZ-22) to the base of the modulator, R1 is the load resistance of the microphone M. The modulator consists of T1, R2, R3, C2, C3, C4, C6, and L1, form a common base capacitor three-point oscillation circuit. Since the base is C2, the high frequency is a base ground, and the audio is the collector ground (the collector electrode is powered by the L1), and the collector junction capacitor CC actually connects both ends of the oscillation circuit, and therefore, The audio signal change, the oscillation frequency varies accordingly, thereby obtaining a frequency modulation signal. Circuit features 1. The modulator uses a direct frequency modulation method with a stable and reliable frequency. 2. The electretal capacitive microphone is used. The microphone has a field effect tube constitutive range of radiobes, which is high, frequency alarne, which uses this microphone to obtain a modulation voltage of the amplitude. 3. All levels have adjustment components, and the debugging is convenient. T1 adjustable C3 to change the frequency, T2 adjustable C7 to obtain a frequency frequency, t3 adjustable C10 to obtain the maximum output. The production of debug line printing board is shown in Figure 3, and the printed board size can be scaled according to the desired zoom. Transistors, resistors, capacitors, microphones can be selected according to the data given in FIG. The battery can be used with a 9V stacking battery; L1, L2, L3 can be wound by φ0.33 enamel wire, the antenna can be used with a tape skin soft wire; K Sub switch. When debugging, press the steps below 1. Check the welded circuit board to ensure that the loading is correct. First measuring the static resistance between the positive and negative power supplies, there is no short circuit or open circuit. 2. Total current. The total current measurement total current is about 50 mA, the B, E pole or short circuit C3 of the forceps short circuit T1, and the current should have significant changes, and the B, E of the short circuit T2 and T3 should also have a significant change. 3. The carrier frequency is measured. The high-frequency voltage of the B poles of T2 with ultra-high frequency millory should have several volts, observed with digital frequency meter, and the distant C3 can be adjusted to the carrier frequency of 45 MHz. The T3 base is tested in the same way, and the adjustment C7 should obtain a carrier frequency of 90 MHz. Then, the frequency gauge and ultra-high frequency voltage meter are connected to the antenna, and the adjustment C10 has a frequency of 90 MHz and the voltage reaches the maximum value. In this way, the carrier frequency is adjusted. 4. Modulation voltage measurement. First short circuit C3, use the millive table to connect to both ends of R4, to the call, and there should be an AC voltage indication, indicating that the microphone and T1 are working properly. If there is no instrument, it can be adjusted by the above steps, and the C3, C7, C10 are repeated, until the received distance is far, the sound distortion is minimized.
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