150mW Crystal AM Transmitter PCB


Posted on Feb 6, 2014

The heart of this circuit is a crystal oscillator. A 10MHz crystal is used to produce highly stable carrier frequency. The sound signal from the condenser mic is amplified by the amplifier circuit consist of transistors Q1, Q2 and Q3. The amplified audio signal modulates the RF carrier generated by the crystal oscillator built around transistor Q4


150mW Crystal AM Transmitter PCB
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. Here, modulation is done via the power supply source line. The amplitude modulated (AM) signal is obtained at the collector of oscillator transisitor Q4. The use of matching dipole antenna and co-axial cable, the transmission range can be increased. The external wire antenna radio receiver can be used to obtain maximum range. The circuit works off a 9V-12V battery. For Modulation transformer X1: You can use audio output transformer found in old transistor radios. Alternatively, you can make it from E/I core transformer lamination with inner winding having 40 turns of 26SWG wire and outer winding having 200 turns of 30SWG.




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