The Effect of the Earth´S Magnetic Field on Absorption for a Single-Hop Ionospheric Path

Magneto-ionic calculations show that deviative absorption is not necessarily negligible at vertical incidence for waves reflected from the E-region at frequencies considerably below the penetration value. Consequently, the value of absorption calculated by the conventional `non-deviative¿ formula for a short-wave oblique path from vertical-incidence absorption measurements tends to be too high. Deviative absorption on paths sufficiently oblique is, however, negligible. The calculations also show the effect of the earth´s magnetic field on Martyn´s absorption theorem to be similar to the effect of losses due to partial reflections: namely to make the absorption in decibels calculated from an oblique path from vertical-incidence measurements too low by a multiplying factor approaching the cosine of the angle of incidence. It is suggested that the absorption to be expected on a radio path might best be calculated by applying the conventional non-deviative formula to measurements made at oblique rather than at vertical incidence.