Asymmetry in the performance of high-frequency radiotelegraph circuits

It is sometimes found that the performance of a trans-equatorial radiocommunication circuit in the high-frequency band differs considerably, at certain times of day, from that in the opposite direction. This phenomenon has been referred to as `circuit asymmetry' and, in the cases considered, it cannot be accounted for in terms of differences in the performance of the terminal equipment. Evidence is produced which tends to show that the asymmetry is sometimes due to the decrease in the signal/noise ratio in one direction which can occur when a distant thunderstorm area, lying in the direction of the main beam of the receiving aerial, reaches its diurnal activity maximum.