Talk about the production and commissioning of the FM transmitter


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Talk about the production and commissioning of the FM transmitter

 

FM transmitter has been subject to many enthusiasts of all ages in a wide variety of radio production projects, in this regard, however, the production involves a number of high-frequency technology, makes a lot of beginners in making debugging such as stop vibration, interference, run frequency, distortion and a series of failures distracted, and even give up. Hand the “FT3S FM transmitter kit circuit, for example, detailed introduces the reader to the FM transmitter alignment experience and common troubleshooting method, hope slightly to help the reader.

Simple class wireless class microphone class is class a typical class wireless class transmitter, class although class the class advantage of class its classinstalled class Serve” class win class the class hearts and minds class of class many class readers. class However class circuit. class Cause class serious class frequency class drift class will enable us to class bear. class Figure 1 circuit class using class the class crystal oscillator class to effectively avoid class the class fatal weakness class running frequency; class octave class amplifier class provided in class the working frequency class band class of class ordinary radio class can be received; class while class RF power class is class raised to class 80mW class level class in class a class multi-stage class highclass frequency class amplifier class in order to achieve class a class more class distant class transmitter.

 

omponentselection

All parts Model parameters is shown in Figure 1; The the miniature color code for high-frequency capacitance as the preferred object, and horizontal installation to reduce the impact of lead inductance; 2. JT selection of nominal frequency 49.860MHz overtone crystal, and other frequency for different output power requirements, can be selected according to the actual situation; 3. Resonant inductor L1, L2, L3 for the frequency and high-frequency amplifier, and suggested the use of Φ0.8mm silver plated wire wound 4.0mm skeleton turns as 5T, 4T, 5T; Vl, V2 determines the highfrequency level noise figure and gain, the choice of the value of β β100-120 in low noise tube about 300, C945, C9014; V3-V5 requirements fT> 500MHz, C1975, C9018, can choose to use. The V6 requires β = 100 fT> 800MHz, Pc> 500mW in the high-frequency power tube, such as C2581, D40, C2053, the output power is not critical, but also to eliminating the need for. TX optional telescopic antenna or 1.5m soft wire, when the operating frequency of 100MHz, 75cm length of the ideal value.

Production debugging

Homemade should be preceded by an assembly of all the components, careful testing and quality parameters, according to the volume required to design a suitable circuit boards. All in all, a good quality components, the appropriate plate layout is effective in improving the self-made success rate guarantee major commissioning steps are as follows:

First, all the components together with the antenna soldered on the printed board, install the welding process requirements: try to reduce the high-frequency part of the component leads; the the resistor capacitor as horizontal installation, no Weld Desoldering phenomenon.
Second, the reference to Figure 2 makeshift welding a simple field strength meter with the debugging.
Third, to the transmitter power, a voltage of 9V. Away from the leads and the antenna of the field strength meter 5cm, to repeatedly adjust the L1 and the distance L2, and L3 interturn to make the field strength meter shows the number increased to the maximum, if necessary, at all levels of the resonance capacitor to adjust.
Fourth, by modifying the antenna length in the small amplitude, so that the field strength meter shows the number continues to increase, and to adjust the transmitting antenna should avoid contact with the human body or metal.
Fifth, and finally the circuit into a metal shield cover to be fixed, and the ground line in communication with the housing.

 

Above the debugging process may seem relatively simple, but not every reader can complete more or less will encounter some troubled Here are some frequently appear in the actual production problems and solutions:
First, close to use, especially when the pickup high signal strength, radio, there is a serious howling or distortion. This is due to the audio amplifier stage gain is high, equipped with electret microphone has a higher sensitivity of the pickup. The solution is simple: simply increase the value of R3 to 820Ω.

AIN interface input source signal, radio output sound small and accompanied hum. This kind of problem, I believe a lot of homemade medium-power high-frequency transmitter friends have experienced. One of the reasons: the use of the filtering effect of the rectifier power caused still can not solve the problem, but if the switch to the battery-powered, it may be because of the high-frequency signal is too strong, the the interference sound source (CD, Walkma, etc.) in the enlarged circuit, resulting in audio output due to contamination, can be improved by the following methods:
1, audio input leads as short as possible;
2, 10uH high frequency inductor in series in each of the two connections of the transmitter and audio;
3 shielded isolation of the sound source;
4, the most direct and effective method is to reduce the output power or shorten the transmitting antenna, so that this method may be considered in the short distance transmission and the need for higher fidelity occasions.

Third, can not afford to vibration or oscillation weak; This failure is manifested in the entire band radio receiving less than static noise, output power, if it is guaranteed the quality of the components, the following steps can help you troubleshoot: 1 in CCend to parallel a 7pF capacitance (Note: this capacitor must not be too large, otherwise you will find that the modulation failure); 2, tone oscillator bias resistor; 3, try changing the C6 capacity, if the above method does not resolve, there may component placementunreasonable cause, re-wiring board.

Fourth, the emission from the past: such issues in addition to the common antenna improper placement, receiving the closing low sensitivity, tall buildings and other reasons, the use of the environment, on the other hand is caused due to the oscillation weak, it is still necessary to refer to the above operationincrease the strength of the crystal oscillator output.
Another reason may be the operating frequency of the frequency multiplier not tune in to the radio reception range, in fact, the radio receives only weak harmonic signal, its performance in the larger field strength meter shows the number of very small but effective firing distance, less than 100 meters (under normal conditions, with a good radio, open to effective distance of about 500-800 meters). Lovers frequency measuring instruments, it is necessary to solve this kind of problem, resonant inductance, capacitance should be strictly in accordance with the above parameters chosen, sometimes also need a careful and patience of the reader, believe in yourself, after repeated adjustment you will solve all difficulties.


Sample/Wholesale
Price
Shipping
Carrier
Buy it Now
1 pcs sample
USD
/pcs
USD
Airmail 25days

pcs
USD
/pcs
USD
Airmail 25days


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