Two-meter, two-watt FM phase-locked transmitter

The circuit directly oscillates to an operating frequency of 144 to 148 MHz without a frequency multiplier. The oscillator is phase-locked to the crystal to ensure oscillator stability. In the 143 to 149 MHz tuning range, the corresponding varactor control voltage is 1 to 4 V, which maintains the appropriate loop gain over the full frequency band. The microphone preamplifier U5 is slightly overdriven, so the speech waveform is clipped or limited. The phase-locked circuit makes the frequency stability as good as the crystal used in the reference oscillator. Dividing the required signal frequency by 25 gives the crystal frequency.