A Frequency Standard for Use at High and Low Frequencies
Rogelio P. McLoughlin · The Journal of the Acoustical Society of America · 1945
A secondary frequency standard is described for use at high and low frequencies, consisting of a tuning-fork oscillator which controls an Abraham and Block multivibrator. An amplifier of adequate selectivity allows the selection of any harmonic of the fundamental voltage. This is accomplished by the use of a multivibrator and a regenerative amplifier of high selectivity which allows selection of any harmonic of the fundamental frequency in the band 1 kc to 2 mc. The tuning-fork oscillator presents the following advantages: 1. Possibility of adjusting the frequency by varying the amplitude of oscillation of the tuning fork. 2. Automatic adjustment of the amplitude to the desired value. 3. Automatic adjustment of the phase difference between the amplitude and the applied force. 4. Visual indication of amplitude. 5. Visual indication of the phase difference. 6. Possibility of manual adjustment of the phase difference. These properties permit indirect measurement of the frequency at any moment making it possible to change tubes without making necessary new calibration by comparison with a primary frequency standard.