The electrical properties of soil for alternating currents at radio frequencies

Abstract

A knowledge of the electrical properties of the ground is of importance in connection with several branches of physics and engineering. A complete study of soil physics, for example, should take account of the electrical, as well as of the other physical properties. In geodetic survey work, particularly when prospecting for oil and minerals, increasing use has been made during recent years of electrical methods, which depend for their success upon a detailed knowledge of the electrical conductivity of the materials of the earth. For the protection of electrical generating plant and distribution networks, it is necessary to provide adequate earth connections at specific points and to ensure that these connections are made in such a manner that their electrical resistance is very small. Similar considerations apply to radio transmitting and receiving stations using earthed aerial arrangements, where it is desirable to make the resistance of the earth connections as low as possible. Apart from these matters, an accurate and detailed knowledge of the electrical properties of the earth’s surface has become necessary in connection with the recent growth of radio communication. Until a few years ago, the main object was to obtain communication over comparatively great distances and on long wave-lengths, when the effect of the earth was not of major importance, but the progress during the past ten years has been such that the effect of the earth is now more obvious. In the majority of broadcasting systems, for example, the service area is generally that covered by radiation transmitted directly along the ground, and the decrease of field intensity with distance is controlled by the electrical properties of the earth. Furthermore, with the widespread use of short wave-lengths for communication, the design of both transmitting and receiving antenna systems is seriously affected by the electrical properties of the ground above which they are erected.