Case of crystal frequency transmitter ----- Crystal FM Transmitter

Case of crystal frequency conversion transmitter, Crystal FM Transmitter Keywords: crystal modulation transmit circuit This paper introduces the production of a frequency modulated wireless microphone, using crystal, and can solve the frequency drift caused by three-point oscillating transmitter well. The machine circuit diagram is shown in the drawings. The entire circuit consists of audio amplification and high frequency oscillation. R2, R3, V1 in the audio amplifier circuit constitutes a collector negative feedback amplifier. The weak signal output from the electret microphone is enlarged. The V2 and peripheral components constitute a parallel crystal oscillator, L2, and C5 resonance on three times frequency of crystals. If a 30 MHz crystal is selected. Then, the center frequency of the transmitted is 90MHz. L1 is a high frequency choke. On the other hand, in order to prevent the rear high frequency signal from slaughtering into the audio amplifier, the other hand is used to provide a static bias voltage to the velocity pipe D1. After the first-level audio amplification, the signal is directly added to both ends of the varactor diode, so that. The oscillation frequency varies near the center frequency as the intensity of the audio signal. Of course, since the Q value of the crystal oscillator is high, the frequency offset of this direct frequency modulation is very small. If you want to get a large frequency offset, you can use a crystal mating multiplier circuit with a low oscillation frequency. The conversion tube in this circuit is selected from the BB910. The author is demolished from the FM radio. The MIC is the electret microphone, and the triode V1 uses a common small power triode, such as 9014, BC547, and the like. V2 uses high frequency small power triode 9018. The crystal is a crystal having a nominal frequency of 30 MHz or 32.768 MHz. If you can buy triple frequency, the frequency can fall to other frequencies of 88 MHz to 108 MHz. it is also fine. L1 uses commercially available color code inductance, the inductance can be between several microengens to dozens of micro. L2 needs to be self-made, and the enamel wire of φ0.6mm can be tightly wound in a cylinder of φ4 mm on the cylinder of φ4 mm. The antenna is used for half a wavelength soft wire. Author: Ji Qing law

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