International comparison of atomic frequency standards via VLF radio signals

A study was made of data obtained over an 18-month period (July 1961 to December 1962, inclusive) on the comparison of atomic frequency standards located in seven laboratories in the United States, Europe, and Canada, using the VLF signals of GBR (16 kc/s), Rugby, England, and NBA (18kc/s), Balboa, Canal Zone. Each laboratory observes the accumulated difference in phase over a 24-hr period (the same for all laboratories, or nearly so) between its own standard (either laboratory or commercially constructed) and the received VLF signal. A statistical analysis was designed to separate the observations at each laboratory into three components: (a) long-term mean differences among the atomic standards; (b) estimates of the standard deviations, &, at each receiving station; and (c) estimates of the transmitter standard deviations, P. Each 2i includes receiver fluctuations, propagation effects perculiar to the path, and measurement uncertainties; 3 includes the transmitter fluctuations and propagation effects common to all paths. units of fractional frequency (that is, 0.39 parts in loto) (GBR data) at LSRH to a high of 1.97 X (GBR data) at NRC with an average for all stations of 1.01 X when measured against NBA. Finally, it is shown that: (1) the means of the frequencies of the seven individual laboratories agreed with the grand mean of these seven laboratories to withink 2 parts in 1010 for the 18-month period, and (2) the laboratory type standards agreed with their grand mean to withink 1 part in loLo.