DIY a simple FM wireless microphone, FM Transmitter
Keywords: FM transmit circuit diagram
Be
Author: Wang Changzhe
1. The wireless microphone principle The electronic microphone is first to turn various sound signals into an audio electrical signal, and this electrical signal re-modulates the high frequency signal generated by the electronic oscillator. Finally, the high frequency signal is transmitted to the air through the antenna. If the transmit frequency is designed in the FM radio band, the high-frequency signal is received in conjunction with any FM radio, and the sound signal is reduced from the high frequency signal to complete various purposes.
2. Circuit diagram The drawing is a circuit diagram of a frequency modulation wireless microphone, a high-frequency triode VL and capacitance C3, C5, and C6 form a three-point high-frequency oscillator. The load C4, L of the triode collector is formed into a resonator, and the resonant frequency is the transmit frequency of the frequency band microphone. According to the parameters of the components in the figure, the emission frequency can be between 88 to 108 MHz, exactly cover the reception frequency of the FM radio, and can easily change the transmit frequency by adjusting the value (coil L) of the L. to avoid the FM station. The transmit signal is then emitted on the antenna by C4.
Be
R4 is the base bias resistance of V1, provides a certain base current to the triode, so that the VL works in the zoom region R5 is a DC feedback resistance, and functions to stabilize the striking workpoint. This frequency modulation principle of such a frequency modulation microphone is to achieve a frequency modulus by changing the base and the emitter of the emitter of the triode. When the sound voltage signal is applied to the substrate of the triode, the capacitive between the triode is synchronized with the size of the sound voltage signal, and the transmit frequency of the triode changes, and realizes the frequency modulation.
The microphone MIC can collect the external sound signal, which is the electret microphone, which is very high, and a weak sound can be collected. At the same time, this kind of microphone must have a DC bias to work, and the resistor R3 can provide a certain DC bias, the greater the resistance of R3, the weaker the sensitivity of the microphone acquisition sound. The smaller the sensitivity of the resistor, the higher the sensitivity of the microphone, the allergy collected AC sound signal is sent to the base of the triode after C2 coupling and R2 matching, and the two diodes in the circuit are inverted in parallel, mainly a two-way limiting function. The diode is only 0.7V, and if the signal voltage exceeds 0.7V, it will be diversified by the diode, which ensures that the amplitude of the sound signal can limit between the positive and negative 0.7V, and the excessive sound signal will pass the triode. Modulation, resulting in sound distortion or even working properly.
Be
Be
CK is an external signal input socket, which can introduce an external sound signal source such as a television headphone socket or a portable headphone socket into the frequency modulation transmitter, and the external sound signal passes through R1 attenuation and D2. Three-pole base for frequency modulation. So this kit can not only make a wireless microphone, but also make a TV wireless headset.
The light emitting diode D3 in the circuit is used to indicate the operating state, and when the frequency of the frequency is actuated, R6 is a current limiting resistor of the light emitting diode. C8, C9 is a power filter capacitor because the large capacitance is generally made of winding process, so the equivalent inductance is relatively large, and a small capacitor C8 can reduce the high-frequency internal resistance of the power supply, which is very common.
KL and K2 in the circuit are a switch. It has three different locations (not painted here, only the description), is disconnected to the leftmost power supply, the rightmost is KL, K2 is connected to the frequency band, the middle The position is KL Turn on, K2 is disconnected, and the wireless repeater is used.
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