Sunspot-cycle variations in the discrepancies between predicted and observed frequencies for use in radiocommunication

A marked variation occurs over the sunspot cycle in the discrepancies between predicted F2-4000km m.u.f. and the observed times of fade-in and fade-out on an 18.4Mc/s Bombay-London circuit. This is particularly marked in summer and is attributed to the influence of the sporadic-E layer, although there is no marked sunspot-cycle effect attributed to this layer. Any assessment of the accuracy of predictions analysed on the assumption of F-layer propagation must be considered in relation to the phase of the sunspot cycle to which it refers