A Review of Primary Caesium Clock Development and Satellite Time Comparison Techniques at NRC

Abstract

The National Research Council of Canada has been active in the development of long-beam primary caesium clocks since 1973, when it was decided to convert the primary frequency standard, CsV, to continuous clock operation. This conversion was accomplished early in 1975, and since then CsV has functioned continuously, providing the physical realization of the NRC scale of proper time, PT(NRC CsV). The two time scales UTC(NRC) and TA(NRC) are derived directly from this scale. The success with CsV led to the decision, in 1976, to construct three smaller primary caesium clocks, CsVIA, CsVIB, and CsVIC, similar in design to that of CsV. These clocks have been in continuous operation since late 1978, and results reviewed in this paper indicate performance similar to that of CsV.

With the development of more accurate clocks, it became of increasing importance to devise better systems of international time comparison based on two-way satellite measurements. Results using a 1-MHz pulse rate for such comparisons are reviewed, and a new proposal involving the use of the upper and lower portions of a commercial television satellite transmission channel is described in detail. Such a system would not interfere with normal use of the TV channel and could provide a convenient, low-cost means of effecting intercontinental time transfer to an accuracy better than a nanosecond.