Some observations on VLF standard frequency transmissions as received at Sydney, N. S. W.

The phase and amplitude of standard frequency transmissions from G.B.R. (16 kc) and N.B.A. (18 kc) are recorded continuously by comparison with a local standard. Equipment developed for this purpose is described briefly and includes a novel digital gear box used to correct the local standard. Diurnal phase variations throughout the year are shown for both stations. Over a 24-hour interval frequency comparisons to better than 1 in 10
¹⁰
are possible although frequency differences between G.B.R. and N.B.A. are not consistent with published comparisons to this order. Some variations due to ionospheric disturbances are noted including the high altitude bomb test on July 9, 1962. Multimode transmission gives rise to interference effects and in the case of N.B.A. the 1-second modulation has been used to differentiate between the long and short path transmissions. Interference between these two transmission paths can lead to an apparent gain or loss of a cycle per day and would present difficulties to an automatic clock synchronizing system based on these transmissions.