On 09/06/2021 13:12, Andrew wrote:

A Google of 'Tropospheric Ducting' and 'Sporadic E' will tell you all.

Yes, but would that explain the almost complete absence of any
signal from 4 of the muxes, hardly any on 48 (BBC SD) but
29 (Quest) was perfectly normal ?.

You have co-channel interference on certain muxes, caused by the
abnormal propagation.

Bill