The accuracy of sky-wave delay measurements

The paper describes an experimental investigation of the limitations imposed by the ionosphere upon the accuracy of sky-wave path-time measurements. The measurements were made at intervals between August, 1942, and the middle of 1944, covering the frequency range 2¿16 Mc/s, and consisted of observations at vertical incidence and at oblique incidence over ranges up to 6000 km. The limiting accuracy of path-time measurement at vertical incidence was found to be of the order of ± 5 ¿sec, while at oblique incidence it was in the region of ± 10 to ± 20 ¿sec under normally favourable conditions. The instrumental techniques involved in the various phases of the work are briefly described, and the probable mechanism of the shortperiod variations about the mean path-time is discussed.