National Physical Laboratory

Why does my radio-controlled clock receive the MSF signal less well at night? (FAQ - Time)

The 60 kHz frequency used by the MSF service was chosen so that users within about 1000 km of the transmitter receive predominantly the ‘ground wave’ signal, which follows the Earth's surface and so has a highly stable path. However, there is also a residual ‘sky wave’ which is reflected off the ionosphere. The ‘sky wave’ component is stronger in winter than summer, and much stronger at night than during daytime. It combines vectorially with the ‘ground wave’ component, and can result in a total received signal that is either stronger or weaker depending on a range of factors including distance from the transmitter, time of day, time of year, and the level of solar activity. The net effect is that the signal strength received during daytime should remain fairly stable, but at night it may vary significantly and give either better or worse reception than usual.

Last Updated: 25 Mar 2010
Created: 9 Aug 2007


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