Intercontinental Frequency Comparison by Very Low-Frequency Radio Transmission

Studies of signals from Rugby, England, at 16 kc and 60 kc have given evidence that a single source of standard frequency can be made available at vlf on a world-wide basis. At a distance of 5200 km the Doppler effects in transmission seldom exceed ±3 parts in 109, and a measurement can be made to 1 part in 109 in a few minutes. Accuracies exceeding 1 part in 1010 are consistently obtained by observation over several hours. Data by Allan, Crombie, and Penton, of the New Zealand Dominion Physical Laboratory, indicate that at 16 kc the diurnal Doppler effects at 18,700 km have normal maxima of the order of 1/108, and that a measurement to 3 or 4 parts in 109 can be made in an hour or less. These results are described and some of the effects of solar flares and magnetic disturbances are discussed. In addition, a brief description is given of four mechanisms that have been found useful in comparing the frequency of a local oscillator with that of a vlf standard transmission.