Some experiments on the accuracy of bearings taken on an aural-null direction-finder

The paper describes some tests to determine how the accuracy of a bearing taken on an aural-null rotating H-Adcock direction-finder depends on the width of the minimum and on the receiver output noise-level. The results pertain to bearings taken on a steady tone-modulated signal by an experienced observer working under good conditions. They indicate that bearings taken under these conditions will have a standard deviation of between 1/40 and 1/20 of the arc of silence except for very small arcs, even when the bearings are derived from very few oscillations of the aerial system. Accuracy is improved if the number of complete oscillations is greater than about five. Differences of at least two to one in the standard deviation of observed bearings may occur between different observers and with one observer at different times. Compared with these changes, any changes due to the use of different receiver output noise-levels are considered to be small. Accuracy is degraded if the angle through which the aerial is swung is increased to improve the quality of the signal at the limits of the swing.