ON THE LONG TERM PHASE STABILITY OF THE 19.8 KC/S SIGNAL TRANSMITTED FROM HAWAII, AND RECEIVED AT BOULDER, COLORADO
NATIONAL BUREAU OF STANDARDS BOULDER CO CENTRAL RADIO PROPAGATION LAB
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The use of VLF signals for intercontinental frequency comparison is now popular, and it was shown that a precision of about 2 parts in 10 to the 11th can be achieved with measurements over a 24-hr period. Phase records made at Boulder, Colo., of the NPM, Hawaii, 18.6 kcs transmission have been studied for several periods of nearly two weeks duration in 1962. Deviations from an assumed linear frequency difference between the transmitter and receiver oscillators show an attainable precision of 2.5 parts in 10 to the 11th in a 24- hr observation, extending to 3.1 parts in 10 to the 12th in a 192-hr observation. Without further data on the remaining differences between the oscillators, there is no evidence that the propagation conditions over the path are limiting this precision. The 50 semiannual variation in the day to night change in phase, if attributed entirely to one level of reflection, would effect precision of frequency comparison of about 1 part in 10 to the 12th.
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