PHASE_LOCKED_100_kHz_REFERENCE

Published:2009/7/6 1:01:00 Author:May | From:SeekIC

Uses 4-MHz crystal in oscillator, with voltage-variable capacitor VVC in parallel with fixed and variable capacitors for setting frequency precisely. Varicap or silicon diode can also be used for VVC. Control voltage for WC is developed by Motorola MC4044P phase-frequency detector and associated MPSA20 amplifier and filter. 7473 and 7490 ICs divide 4-MHz signal by 4 and then by 10 to give 100 kHz. Main output can be further divided with additional 7490s, down to 60 Hz for driving electric clock if desired. Adjust C3 and R1 for symmetrical square wave at pin 1 of MC4044P, with clean leading and trailing edges. Typical values are 68 pF for C3 and 300K for R1, but values will depend on transistors used. Transistor types are not critical. Gates U2B and U2C with Q3 form lock indicator circuit that turns on LED when 4-MHz oscillator is phase-locked to output of external high-stability 100-kHz frequency standard. U1 and U2 are SN7400.-C. A. Harvey, How to Improve the Accuracy of Your Frequency Counter, Ham Radio, Oct. 1977, p 26-28.



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