Method and apparatus used in testing piezo oscillators for broadcasting stations
E.L. Hall · Bureau of Standards Journal of Research · 1930
Piezo oscillators are the most suitable frequency standards thus far devised for use in radio broadcasting stations.A piezo oscillator may be used either to check the frequency of the station or to control its frequency.Most of the piezo oscillators tested by the bureau are for use in checking the frequency of the station.Piezo oscillators are capable of high precision in the measurement of their frequency if a beat note is produced by adjusting another generator to a similar frequency.This principle is employed in the methods and apparatus described in the paper.After preliminary tests to determine the suitability of the quartz plate and its fundamental frequency, the piezo oscillator is kept in a temperature-controlled room for not less than two days, during which frequency measurements are made.The method consists in measuring the frequency of the piezo oscillator under test in terms of a 200 kc temperature-controlled piezo oscillator.This is accomplished by adjusting a radio-frequency generator to the frequency which the piezo oscillator under test should have.This adjustment is made by using harmonics from a 10 kc generator which is kept accurately set in terms of the 200 kc stand- ard by observing a special form of beat indicator.The frequency difference between the test piezo oscillator and the generator set in terms of the standard is measured by comparison with an audio-frequency generator.A frequency meter of special design is used to check the frequency difference and determine the sign of the correction to be applied.The method described is also useful in the calibration of frequency meters and the measurement of station frequencies.CONTENTS Page I. Piezo oscillators as frequency standards for broadcasting stations 115 II.Testing method 116 III.Description of apparatus 120 1. Temperature-controlled room