2Pcs FM Radio Microphone Transmitter Module DC 3-6V 80MHz-108MHz PCB DIY Kits

Description

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Description:
The transmission frequency of this circuit is about 90MHz. The receiving equipment adopts ordinary FM radio. Adjust the inductance L to adjust the transmission frequency so that the frequency avoids the local radio station. The working voltage of the circuit is DC 3V-6V. The transmission distance of this kit is about ten to dozens. Meter, the transmission distance is related to the power supply voltage, antenna length matching and impedance matching, the degree of openness in the area, electromagnetic interference, and the sensitivity of the receiving equipment.
Parameter:
Frequency range: 80MHz—108MHz
Working voltage: DC3V—6V
Note:
This module is a loose part and needs to be welded by yourself. If damage is caused during the welding process, we will not be responsible for the replacement.
MIC is an electret microphone, its function is to sense the weak vibration of sound waves in the air, and output the same electrical signal as the sound changes. This site uses a microphone with high sensitivity, which can generally output an audio signal above tens of millivolts, which is sufficient to modulate the frequency of the high-frequency oscillation signal of the next stage. Note: The microphone is divided into positive and negative poles. Generally, the negative pole is connected to the shell.
R1 is the bias resistance of the MIC electret microphone. With this resistance, the microphone can output audio signals. This is because the MIC microphone itself has a FET amplifier circuit for impedance matching and improving output capacity.
C2 is an audio signal coupling capacitor, which delivers the sound electrical signal induced by the microphone to the next level.
C2 is the base filter capacitor of Q9018. On the one hand, it filters out high-frequency noise. On the other hand, it makes the high-frequency potential of Q9018 0. For high-frequency circuits above 50MHz, Q9018 is a common base amplifier circuit. Finally, it can form the basis of oscillation. Because the basic condition of the oscillating circuit is that it must have a certain gain, and then the feedback with the appropriate phase (usually positive feedback).
R2 is the base bias resistance of Q9018, which provides a smaller base current to Q, and Q will have a larger emitter current to pass through R3. Because the current in R2 and R3 will produce a voltage drop on their respective resistances and affect each other, the result will automatically stabilize at a certain value state, which is the emitter follower mentioned in the book.
R3 is the emitter resistance of Q9018, which acts as a stable DC operating point, and C6 also forms a high-frequency signal load resistance, and is also a part of the entire high-frequency oscillation circuit.
C4 and L form a parallel resonant circuit, which plays a major role in selecting the oscillation frequency. Changing the capacity of C4 or changing the shape of L (including the number of turns) can easily change the transmission frequency.
C7 is a high-frequency signal output coupling capacitor, the purpose is to make the high-frequency signal into a radio wave radiated into the sky. Therefore, the antenna is best to be straight up, the length should be equal to the wavelength of the radio wave frequency (or an integer multiple), and the surrounding area should be open and not blocked by metal objects. Note: The wavelength is equal to the reciprocal of the frequency. When the frequency changes, the wavelength will also change. Besides, the specific length of the antenna is also related to the output impedance of the circuit, the thickness of the antenna, etc. In an amateur, just connect a piece of wire. (If you want to pursue the farthest launch distance, you can try more on your own. The component package of this site has been tested by our technicians, and the effect can easily reach 50 meters away.)
C5 is the feedback capacitor, the key component of the circuit to start oscillation is it. When analyzing the high-frequency state of this circuit, the collector is the output, and the emitter is the input. The output signal is added to the input through C5, which produces a strong positive feedback, which naturally causes oscillation. This is actually the capacitor three-point oscillator circuit mentioned in the book.
C1 is the power supply filter capacitor, which provides a loop for the AC signal and reduces the AC internal resistance of the power supply.
TX connected to antenna: You can connect a piece of wire as an antenna, the antenna should not be too long, so as not to affect the frequency stability
Debugging:
Connect the power supply and antenna test, the antenna can use 20-40 cm thick wire (the antenna should not be too long, so as not to affect the frequency stability), not provided in the kit, you need to bring your own. The receiving device adopts an FM radio to adjust the tightness of the inductance coil on the simple wireless microphone, so that the signal from the microphone can be received on the radio.
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2Pcs FM Radio Microphone Transmitter Module 80MHz-108MHz Kit DIY
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