Precise T&F Inter-Comparison via VLF Phase Measurements

A. Sen Gupta, G.K. Goel, B.S. Mathur

Abstract: The Indian subcontinent does not fall in the ground wave range of any LORAN-C transmission. As such, at present the only alternative technique in this region for convenient and routine T & F intercomparison is via VLF phase measurements. At NPL, New Delhi, continuous phase recording of the 15 kHz transmissions from GBR (UK) is being made. In addition the published midday phase data of GBR from several laboratories-NPL (UK), RGO(UK), PTB (PRG) and USNO (USA) - are being received regularly. In the present paper we discuss T & F intercomparisons between the local time scale, UTC (India), at NPL and those at the above mentioned laboratories, using the VLF phase data. A major factor which limits the accuracy of long term comparison is the seasonal variation in the VLF propagation delay over long paths. It is shown that by taking into account the seasonal propagation delay variations in a semiempirical way the accuracy of T&F comparisons can be considerably improved. In fact over a one year period accuracy of few parts in 2014 in frequency and 1-2 sec in time have been obtained. The relative frequency offset difference between UIC (India) and UTC (PTB) evaluated in the present work as (7.0 + 0.1)x10-13 agrees very well with that obtained via the satellite experiment described in a companion paper.
Published in: Proceedings of the 12th Annual Precise Time and Time Interval Systems and Applications Meeting
December 2 - 4, 1980
Goddard Space Flight Center
Greenbelt, Maryland
Pages: 851 - 862
Cite this article: Gupta, A. Sen, Goel, G.K., Mathur, B.S., "Precise T&F Inter-Comparison via VLF Phase Measurements," Proceedings of the 12th Annual Precise Time and Time Interval Systems and Applications Meeting, Greenbelt, Maryland, December 1980, pp. 851-862.
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