The effect of the shape of the transmitting aerial upon observed bearing on a radio direction-finder

For the explanation of the variable errors encountered chiefly at night on radio direction-finders, modern theory implies the reception of waves arriving at an appreciable angle of elevation and polarized so that the magnetic field has a horizontal component in the plane of propagation. Previous experimenters have shown that such abnormally polarized waves can be radiated from certain kinds of aerials when situated at a considerable distance from the earth´s surface, as in the case of an aeroplane transmitter, and that such waves when arriving at the earth´s surface can produce very appreciable errors on a radio direction-finder. The experiments described in the present paper were carried out to determine to what extent the emission of these abnormally polarized waves by aerials of different shapes from a ground transmitting station was responsible for the frequent occurrence of variable ¿night¿ errors at a ground direction-finding station. It is concluded that the frequency and magnitude of these errors are independent of the shape of the transmitting aerial, within the limits of this investigation, and that the use of a source of radiation which is, as far as possible, only polarized in the normal manner, in no way diminishes the night effects generally experienced.