2_W_2_METER_PHASE_LOCKED_FM_TRANSMIT_TER

Published:2009/7/2 23:13:00 Author:May | From:SeekIC

Operating frequency of 144-148 MHz is generated directly, without using frequencymultiplier stages. Oscillator stability is achieved by phase-Iocking oscillator to crystal. Tuning range of 143-149 MHz corresponds to varactor control voltage of 1-4 V, which maintains proper loop gain across entire band, ECL decade divider U2 is Plessey SP647 driving Schottkyclamped divider U3B to give overall division of 50. Phase detector and Ioop amplifier functions are in U4. Pierce crystal oscillator Q3 feeds buffer Q4 interface with TTL levels. Microphone preamp U5 is slightly overdriven so speech waveform is clipped or Iimited. With phaseIocked circuit, frequency stability is as good as that of crystal used in reference oscillator. Divide desired operating frequency by 25 to get crystal frequency.-A. D. Helfrick, A Phase-Locked 2-Meter FM Transmitter, QST, March 1977, p 37-39,



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