A standard of frequency and its applications

The paper discusses the importance of frequency standardization to the telecommunication engineer, and outlines the work which the Post Office has carried out in this field. As published information on the subject is scanty, the historical development of frequency standards is reviewed, a bibliography is included and the factors affecting the design of a standard are briefly analysed. The design, performance and application of the Post Office standard are considered in some detail. In particular, the absolute calibration of the group of crystal-controlled oscillators comprising the standard is discussed, and details are given of equipment designed for the precise intercomparison of the frequencies of the individual oscillators. A specialized form of frequency standard, known as a ¿quartz clock,¿ which is now being used by astronomers in addition to the older type of pendulum clock, is briefly described. The methods available for the comparison, both national and international, of frequency standards are analysed, and a résumé of international comparisons reveals the advances achieved in frequency standardization during the past two decades. At present it is considered that the absolute value of the Post Office standard of frequency is known to ±1×10¿8. Finally, the development work now being carried out to improve the stability and reliability of the standard is outlined.