The Accuracy of Frequency Standards disseminated by HF Radio Paths through the Ionosphere

Abstract

The 12 MHz VNG standard frequency transmitted from Lyndhurst has been phase compared with a local standard at Townsville over a total of 54 days. The Doppler shift introduced by the one ionospheric reflection has a diurnal trend which is predictable from the ionosphere parameters fo F2 and M3000F. The optimum time of day for frequency dissemination using VNG 12 is between 1100 and 1530 h. Faster fluctuations generally obscure the diurnal trend, however, and an accuracy of ± 0·1 Hz on the 12 MHz carrier is attainable only by averaging the incoming frequency over a 1 h period. Spectral analysis of the fluctuations in frequency show significant spectral amplitudes down to short periods of about 1 min where the time resolution of the measurements provides a cutoff.