Non Reciprocal Ionospheric Propagation in the Medium Frequency Broadcasting Band

Measurements made in the U.S.A. suggest that east-west ionospheric propagation in the medium-frequncy broadcasting band is non-reciprocal. A possible explanation is put forward in the paper, which draws attention to the fact that the combination of polarisation-coupling loss and ground-reflection loss which occurs between hops on multi-hop paths depends, in general, on the direction of propagation.