A small FM transmitter circuit

1. Introduction:

    
Here I would like to introduce simple and easy system for small FM transmitter. It not only meets the requirements of launch distance, but also while using a microphone and line input audio signal, the background voice. Modulation monitor circuit also joined the header in order to better understand and use well the transmitter, the circuit as shown below, read the brief, whether they think it is like a radio station equipment as many functions. Yes, it sets a small transmitter can help you easily put up an FM radio amateur! Coverage about the 500M. Heart of it, immediately it!

 

 

 

2. Circuit and component selection:

Exposure to the microphone signal by the C1 coupling into the BG1 and external circuit voltage feedback single-tube amplifiers, the voltage signal weak enough to enlarge the scope and U1A amplified with the line input signal into the mixed U1B. Mixed signals all the way through R17 to the modulation and around the BG2 FET test circuit composed of recent comparative LC oscillator, LC oscillator, the characteristics of recent comparative test is a simple and ordinary capacitance three-point oscillator, at the same time with high efficiency and high stability. Good waveform, modulation bandwidth, this FM transmitter for amateur production is particularly important. After the final cast by BG3 level amplifier fired out through the transmitting antenna, you can listen to an ordinary FM radio broadcast. Another way signal amplifier formed by U1C and then simply wave rectified by D2 microammeter DC drive, near the monitor signal modulation amplitude. Transfer system, generally do not use more than 85% is appropriate. Integrated circuits and other common use of LM324 quad op amp, to form a single power supply back to input mode, both the positive phase input voltage is set at half the supply voltage. Surveillance-type header for the 200u, BG1.BG3 use 2SC1815. BG2 with 3DO2 FET, D2 varactor diodes used 1S2267. Antenna requires the use of 1 / 4 wavelength, such as the use of the whip antenna is best not to less than one meter. Otherwise, results will fall short of late launch.

3. After the words:

This circuit is not my design, is the shortage of the early years of e-information, I picked up from the broken heap of an extract from the magazine did not name, and adaptation. The original circuit with a plate and assembly drawings. Such Digest magazines to the present has been rare. Thanks to the original author of this again! Note that transmitter, do not interfere with the normal use of radio broadcasting. Finally I wish you happy playing.

 

2. Circuit and component selection:

Exposure to the microphone signal by the C1 coupling into the BG1 and external circuit voltage feedback single-tube amplifiers, the voltage signal weak enough to enlarge the scope and U1A amplified with the line input signal into the mixed U1B. Mixed signals all the way through R17 to the modulation and around the BG2 FET test circuit composed of recent comparative LC oscillator, LC oscillator, the characteristics of recent comparative test is a simple and ordinary capacitance three-point oscillator, at the same time with high efficiency and high stability. Good waveform, modulation bandwidth, this FM transmitter for amateur production is particularly important. After the final cast by BG3 level amplifier fired out through the transmitting antenna, you can listen to an ordinary FM radio broadcast. Another way signal amplifier formed by U1C and then simply wave rectified by D2 microammeter DC drive, near the monitor signal modulation amplitude. Transfer system, generally do not use more than 85% is appropriate. Integrated circuits and other common use of LM324 quad op amp, to form a single power supply back to input mode, both the positive phase input voltage is set at half the supply voltage. Surveillance-type header for the 200u, BG1.BG3 use 2SC1815. BG2 with 3DO2 FET, D2 varactor diodes used 1S2267. Antenna requires the use of 1 / 4 wavelength, such as the use of the whip antenna is best not to less than one meter. Otherwise, results will fall short of late launch.

3. After the words:

This circuit is not my design, is the shortage of the early years of e-information, I picked up from the broken heap of an extract from the magazine did not name, and adaptation. The original circuit with a plate and assembly drawings. Such Digest magazines to the present has been rare. Thanks to the original author of this again! Note that transmitter, do not interfere with the normal use of radio broadcasting. Finally I wish you happy playing.

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