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An experimental crystal oscillator FM transmitter circuit

2014-11-16 02:38  
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An experimental crystal oscillator FM transmitter circuit
As shown in Figure 1, V1 and related resistive and capacitive components form the first level audio amplifier circuit which provides sufficient strength audio signals for modulating level. D1 is variable capacitance diode, and its equivalent capacitance varies with the reverse voltage on two poles, thus enabling center frequency of oscillator composed of crystal oscillator and external circuit change to achieve the purpose of FM. The signal output by oscillator is frequency doubled, amplified by the V3, then it is output by the tuned transformer after completing matching and filtering. The circuit uses tuned transformer, so it needs to restructure their cores after finished making. Its method is to produce a simple field strength circuit (as shown in Figure 2) to connect with the output terminal of the transformer, then adjusting the magnetic core until the ammeter indicating the maximum value.