Wireless FM microphone single tube FM transmit circuit DIY electronic production

The circuit schematic of the wireless frequency-frequency microphone is shown below, where the LC parameter is an important factor in which the circuit is oscillating and the transmission frequency is high, in particular the L and C3 in the resonant loop, which determines the frequency modulated frequency, whether the production is successful or not key. The author has been derived by theoretical derivation, accurately measured and installed verification. Use the following formula to select the resonant loop LC value accurate and reliable. The formula is: n = 2.565 × 107d / φ2f2c, where n, d, φ, f, and c represent the number of turns of the resonant coil L, the diameter of the lacquerable copper coil, the inner diameter of the coil (i.e., the diameter of the temporary skeleton with the coil ), Emission frequency, resonant loop capacitance value. The orders used in the formula are the utility units, respectively:, millimeters, MHz, peptotherapy. For example, the resonant capacitor C is selected from 15 pF, and the transmitted frequency is 96 MHz. If the lacquer cable of D = 0.6 mm can be wound around the coil in a common ballpoint pen in diameter φ = 3.5 mm, and the calculation is calculated by the above formula. 9.1, actually winding 9. Note: (1) The number of turns calculated according to this formula means that the single layer is wound, that is, the turns and turns are closely arranged, and the gap is not left, and the wound is ready. Painted copper wire (better silver wire) is as large as possible, which can reduce the loss resistance of the coil to improve the quality factor Q to increase the gain of high frequency oscillation circuits. (2) When using this formula, the parameter values ​​are appropriately adjusted, so that the transmit frequency is between 88 MHz-108MHz, and the edge frequency is not close to the edge frequency. And the number of turns is integer. In addition, C4 determines the band width, generally selected 3-10p, preferably from 5-8p, and the C2 is related to the depth, generally select 100-300P (some circuits, the capacitance is between the base and the ground.) Capacitors having a capacity of 500-1500p, C5 is an antenna signal coupled capacitor, and select capacity at 10-20p. Transistor BG high-frequency operation state, the cutoff frequency is greater than the need to use high-frequency transistor 100MHZ, and the collector junction capacitance is smaller. After the actual installation, it is easy to debug success with 3DG204, 3DG56, 3DG80, 9018, etc., which is worse than the 3DG6, 3DG201, etc. Sex is better. The P value of the triode is not appropriate to be too high, which is better between 60-100 to avoid unstable oscillation frequency. Installation points The elements of the high frequency part are short, and the pin must be short. On the one hand, it is to reduce interference, which is conducive to the normal operation of the circuit, and on the other hand, it is accurate and stable to make the transmit frequency between 88-108 MHz. If the pin of L or C3 is too long, it is equivalent to increasing the, thereby increasing the amount of inductance, and is even equivalent to an increase of one or two, but also to increase the resonance for only a few turns cut diameters. There are a lot of frequencies, this is not ignored. Component layouts are separated by high and low frequency, and connectors do not intersect each other. There is a gap between adjacent printed lines on the circuit board. The welding is reliable and smooth. The schematic line chart is shown below. Be Circuit debugging and troubleshooting 1, make the circuit normal Determining whether the oscillating circuit, which is convenient and feasible approach: in the power circuit or play table string mA to 10mA in the multimeter profile, monitors the machine current, the metal rod so that when the handheld screwdriver BG reach the collector, the current should be Increasing changes, after leaving, recover the value, that is, proves that high frequency oscillation work is normal. When the contact is hit, the current value changes great, indicating that the oscillation is strong, if the circuit is not changed, the circuit does not ode. The causes of the circuit are not hosted: (1) DC operating point is inappropriate: by adjusting the bias resistor R2, the whole machine is between 2-3mA (3-7mA to the 3V power supply); (2) BG High frequency energy difference or installation is damaged, it is necessary to replace it; (3) C2, C4 is not properly selected, deviation from normal value; (4) C2, C3, C4 has a short circuit, open circuit failure. For short circuits, it is easy to measure with general methods. It is difficult to judge the circuit failure without the capacitance table, but such faults may be small. (5) Circuit board or solder joints include short-circuit and fake solder joints, need to be carefully examined, refolde. Also do not use non-insulated or corrosive flux such as zinc chloride solution, solder paste, which will make the wire board insulation performance, serious leakage of the element, if used, can use pure wine, after cool Combatch again. 2, the circuit starts. However, the receiving signal has been demonstrated that the circuit is normalized by the above method, but the receiving point is not found throughout the radio modulation section, which is due to the L, C3 value in the resonant loop, causing the oscillation frequency to be more than the modulation section. The frequency range, the initiator installation is not successful. The solution can be solved by trying C3 or proper stretching or compression. This case is mostly caused by the nominal value error of C3. If the value of the C3 is measured with the capacitance table, the above-described phenomenon does not occur with the above formula. 3, work unstable The main stability is mainly: (1) BG performance or β value is too low; (2) The value of C4 is too large or too small; (3) Welding or the internal contact of the component; (4) transform or handheld different positions When the operating frequency is unstable, since the single tube is easily induced by the human body, the frequency offset is approximately, and the radio frequency is rotated, the frequency, or the screen disadvantage is solved. 4, the sound is small. Moonlight. (1) High frequency vibration weakness: The transmit power is too small or the receiver is too far, it can appropriately adjust the R2 and the tube of the P value slightly high, to rewound L, appropriate long launch antenna Waiting for improvements; (2) The microphone is not good, or the bias resistor R 1 impaired value (the phenomenon is often a small small and the noise is not necessarily large), the adjustable R1 makes the A-point voltage to 1/2 of the power supply voltage, make the sound maximum Do not live; (3) The receiver is not allowed, and the received parasitic oscillation frequency is received. If no noiseous reception points are found throughout the band, the faults of the above "circuit oscillation, but not finding the table" can be processed.

Leave a message 

Message List