Comparison between the measurement and prediction of HF radio signals propagating along the mid-latitude trough

Between October 2000 and January 2002, measurements of the carrier-to-noise density ratio, time-of-flight and direction of arrival were made for radio signals in the lower HF band received over a path from Uppsala, Sweden, to Leicester, UK. These observations were compared with the corresponding predictions given by VOACAP with the following results: during the summer at all times, and during the day in winter, there is a very good agreement, while at night (in winter) the agreement is poor. The poor agreement arises because of the off-great circle path propagation often found at these times. The off-great-circle propagation is consistent with the signal being scattered from irregularities in the north wall of the mid-latitude trough.