Abstract :
The problem dealt with is the calculation of the effective e.m.f. induced in a receiving antenna from the field of a neighbouring transmitting antenna. It is assumed that the distribution of the current in the transmitting antenna is known. In this connection the author has shown that, for the simple antennae usually met with in practice, the current distribution can bereadily calculated. The various parts of the problem are taken separately. First, the formulae for the field at a point due to any element of current are given, and it is shown that the wave-form of the field varies with the distance from the antenna. The next point deals with the polar diagram at large distances of an antenna. With regard to the wave-form, it is pointed out that the usual spectrum of the current of a radio station consists of a number of peaks at frequencies which are whole multiples of the first, each peak havinga fairly rapidly decreasing intensity for a comparatively small range of frequency on each side.The peaks correspond to the fundamental and the harmonics, and on each side are the side bandsof the modulation. It is pointed out that the polar diagram of the harmonics may differ very considerably from each other, but that, for the frequencies of the side bands, the directions of the maxima of radiation would not be appreciably different from the directions of the maxima of the corresponding harmonic. The effect of the conductivity and dielectric constant of the earth is next considered, the image due to any given element of current being taken as the exact image of the current element, but having K times the intensity. The factor K
