Make A Crystal-Locked FM Transmitter

The Crystal-Locked FM Transmitter project builds a stable radio frequency transmission system using analog and discrete electronics. Audio input is first received and processed by an LM386 audio amplifier IC, which boosts the signal to an appropriate level for modulation. Instead of relying on a standard, drifting LC oscillator, this circuit achieves frequency stability using 24MHz crystals (XTAL1 and XTAL2) within its oscillator stage. Because the desired operating carrier frequency is 96MHz, the circuit employs 2N3904 transistors in a frequency multiplier configuration to step up the 24MHz crystal frequency by a factor of four. A higher-power 2N3866 transistor acts as the final radio frequency amplifier stage to boost the multiplied carrier signal before it reaches the antenna wire. Tuning is assisted by a trimmer capacitor (VC1) to optimize resonance. Diodes such as the 1N4007 and 1N4148, alongside a network of inductors, capacitors, and resistors, are utilized throughout the power distribution, biasing, and decoupling stages to ensure stable DC operation and proper signal routing on the custom PCB.