Comparison of C;æsium Frequency Standards of Different Construction

Abstract

COMPARISONS between the National Physical Laboratory standard and an ‘Atomichron’, by means of standard frequency transmissions¹, indicated an average difference of 4 parts in 10¹⁰ with a standard deviation of 4 parts in 10¹⁰. Comparisons made by means of time signals in the course of a joint programme being carried out by the National Physical Laboratory and the U.S. Naval Observatory gave a larger difference, 9 parts in 10¹⁰. This difference was discussed at the meeting of the Consultative Committee for the Definition of the Second at Sèvres in June 1957 and in a paper submitted by Dr. W. Markowitz to the XIIth Assembly of the International Scientific Radio Union at Boulder in August 1957. The desirability of carrying out direct comparisons in the same laboratory between the National Physical Laboratory standard and the ‘Atomichrons’ was emphasized at both meetings. Such comparisons have recently been made at the National Physical Laboratory, Teddington, in collaboration with the United States Army Signal Engineering Laboratories, Fort Monmouth, as the agency which initiated the project and supplied the ‘Atomichrons’, and the National Company Inc., of Maiden, Massachusetts, as the contractor of the U.S. Army Signal Engineering Laboratories.