Interpolation Methods for Use with Harmonic Frequency Standards

Interpolation methods for determining the value of an unknown frequency in terms of harmonic standard frequencies are discussed under the following classifications: I. Direct beating methods, wherein the beat between known and unknown frequencies is utilized directly to operate frequency indicators or measuring devices. II. Direct interpolation methods in which the fundamental frequency of an interpolation oscillator is adjusted to zero beat in turn with the unknown frequency and the adjacent known harmonic frequencies. The unknown frequency is then found from the oscillator dial readings. III. Harmonic interpolation methods which are an extension of the principles of (II) permitting an interpolation oscillator of limited fundamental frequency range to be employed in the measurement of frequencies lying both above and below this range. IV. The principles of (III) point to a means for covering a wide range of unknown frequencies through the use of a low-frequency narrow-range oscillator fitted with harmonic producing circuits. A greatly opened-out interpolation scale may be obtained. Some disadvantages and limitations of the various methods are considered, as well as some advantages.