Keywords: production and commissioning of crystal frequency frequency transmitter, FM transmitter circuit
Production and commissioning of crystal frequency frequency transmitter
In the five-flowered radio production project, the FM transmitter has been favored by many enthusiasts. However, in this area, the production involves some high-frequency technologies, making many beginners in making commissioning, such as stopping, interference, running frequency, A series of faults such as distortion is upset, and even give up. In this paper, the "FT3S FM Emitter Suite Circuit is used as an example," introduces the reader to the reader's installation experience of the FM transmitter, and I hope that the reader is slightly helpful. Simple wireless microphone is a wireless transmitter Typical, although the advantages of "one installation" will win the favor of many readers. However, in the circuit. The serious frequency drift will be unbearable. Figure 1 The crystal oscillator used by the circuit effectively avoids "running frequency" "This depends on the weakness; the multiplier amplifier sets the operating frequency on the conventional band of the ordinary radio; the multi-stage high-frequency amplifier increases the RF power to 80MW level to achieve a farther distance.
Component selection: All part model parameters are shown in Figure 1; 1. Mini color code high frequency capacitors are preferred objects, and use horizontal installation to reduce the impact of lead inductance; JT uses a nominal frequency of 49.860 MHz, which can be used to select other frequencies according to the actual situation for different output power requirements; 3. L1, L2, L3 is multiplier and high frequency amplifier resonant inductance, it is recommended to use φ0.8mm silver-plated lines to wind on 4.0mm skeleton, and the number of turns is 5T, 4T, 5T; VL, V2 determines the high frequency stage. The noise coefficient and gain, optional β value is low noise, such as C945, C9014, etc .; V3-V5 requires β100-120, ft> 500MHz, C1975, C9018, etc. can be used. V6 requires β = 100, ft> 800MHz, PC> 500mW high-frequency medium power tube, such as C2581, D40, C2053, and it can be saved when the output power requirement is not high. TX can be used with a rod antenna or a 1.5M soft wire, and 75 cm length is an ideal value when the operating frequency is 100MHz. Production and commissioning: All components should be collected first before homemade, and the quality and parameters are carefully detected, and then the appropriate circuit board is designed according to the required volume. All in all, good component quality, suitable printed board layout is a guarantee that effectively improves self-made success rate, the main debugging steps are as follows: 1. Welding all components along with the antennas, on the printed board, to install the welding process requirement: minize as shorten High frequency partial component leads; resistance, capacitors as horizontally installed, no duly welding, demymement.
Second, refer to Figure 2 temporarily offering a simple field, a high-grade, a debugging commissioning. Third, the transmitter is powered, the voltage is 9V. The field strong lead wire and the antenna are 5 cm, repeatedly regulates L1, L2, and L3 hut distance to maximize the field strength count, if necessary, the resonant capacitance at each stage is adjusted. 4. By modifying the length of the antenna in a small size, the field strength count continues to increase, and pay attention to the adjustment, the transmit antenna should avoid contact with the human body or metal. V. Finally, the circuit is placed in the metal shield and communicates with the outer casing. The above debugging process seems to be relatively simple, but not every reader can be completed smoothly, or more or less will encounter some troubles. Here is some problems and solutions that often appear in actual production:
First, when using the near-distance, when the signal is high, the radio is severely treated or distortion. This is due to the high increase in audio amplifier, and the electret microphone applied is caused by higher pickup sensitivity. Solution is simple: just increase the resistance of R3 to 820Ω. Second, when entering the sound source signal with a AIN interface, the radio output is small and accompanied by communication. Such problems, I believe many friends from the self-made high-frequency transmitter have experienced. One of the reasons: Since the rectifier power supply is used, the problem is not solved if the battery is powered, it may be because the high-frequency signal is too strong, interfering the source (such as CD, Walkma, etc.) amplification circuit. The output audio can be improved by the following methods: 1. Try to shorten the audio input leads; 2, in each of the transmitter and the source two lines of 10UH high frequency inductance; 3, shield the sound source; 4, the most direct and effective way should be used to reduce the output power or shorten the emission antenna, which can be considered in applications where close-to-transmission and require high fidelity. Third, no vibration or vibration, this fault is not received in the entire band, the output power is small, and the output power can be guaranteed, the following steps can help you exclude failure: 1, on both ends of the CC A 7PF capacitor (note: This capacitor is not too big, otherwise you will find the modulation failure); 2, adjust the oscillating level bias resistor; 3, change the C6 capacity, if the above method does not solve, it is also possible to be the component layout Reasonably, the board can be re-routed. Fourth, the emission distance is close to: This type of problem is not properly placed in the common antenna, the receiving sensitivity is low, and the use environment has a high building, and on the other hand, due to the weakness of the oscillation, there is still a need to refer to the above operation. Crystal oscillator output strength. One reason may be that the frequency of operation of the multiplier is not adjusted within the radio receiving range. It is actually a weak harmonic signal received by the radio, and its performance is in a large number of field strength, but the effective emission distance is small, not By 100 meters (under normal conditions, with a good radio, the open effective distance is about 500-800 meters). For those who have no frequency measuring instruments, to solve such problems, in addition to resonant inductance, capacitance should be strictly selected by the above parameters, sometimes need a careful and patience of readers, believe in themselves, after multiple adjustments You will solve all difficulties.
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