Some simultaneous observations on downcoming wireless waves

Abstract

The present communication deals with a series of observations on downcoming wireless waves made simultaneously at three receiving stations, situated at different distances from the wireless sending station. The original series of experiments, of which this series is a development, was carried out chiefly over a distance of transmission of about 80 miles. This distance was chosen because, for the 400-metre waves used, the intensity of downcoming waves, at night, is an appreciable fraction of the ground wave intensity, so that conditions are specially favourable for the detailed study of the various characteristics of downcoming waves by methods in which the ground waves are used as reference waves. There seemed, however, many reasons for making observations at shorter distances if downcoming waves could be satisfactorily detected there, while there was more to justify the simultaneous use of several receiving stations than the mere confirmations given by duplicate measurements. For example, it was realised that, according to the ionic refraction theory of the atmospheric deviation of wireless waves, the minimum electronic density necessary to bend back the waves increases as the angle of incidence is decreased, so that measurements of the equivalent height of the ionised layer at different distances might be expected to yield information relating to the gradient of ionisation in the layer, a subject on which precise information is entirely lacking. Further, the results of single station working between Teddington and Peterborough had suggested that, during the few hours before sunrise, the region of ionisation, which normally reflects 400-metre waves, often becomes penetrable for waves of a certain angle of incidence, there being, on such occasions, discontinuous changes in the results of a series of measurements of the equivalent path of the atmospheric rays. It appeared, therefore, of interest to test whether such phenomena were simultaneously observed for atmospheric waves of different angles of incidence such as would ultimately be received as downcoming waves at different distances. Finally, although estimates have been made of the reflection coefficient of the ionised region for particular distances of transmission, there were no data relating to the variation of the atmospheric wave intensity with angle of incidence, such as could only be obtained from simultaneous observations on the radiation from the same transmitter. It is obvious that this last-mentioned subject is of more than scientific interest for it has an important bearing on the practical problem of the prediction of the service areas of broadcasting stations at night. The account of these investigations, given below, is divided into two sections, numbered (2) and (3), dealing with the measurements of equivalent height and the measurements of reflection coefficient respectively. These are followed by a general discussion of results (Section 4).