chapter  15
28 Pages

Different Issues

WithBoris Levin

Reliable underground radio communications are required for many applications, example for communication between people, working below ground and on the ground surface. The ratio between the two signals at the receiving point depends on a distance between the correspondents, on a placement depth of transmitter and receiver, and on electromagnetic characteristics of the ground layers along the channel. As a rule, the signal, propagating by the first way, is greater. Electromagnetic interference in communication channels is caused not only by cable asymmetry, but also by asymmetry of excitation and load, which provokes the emergence of the in-phase currents in cables. The wire capacitance per unit length also varies only slightly, that is, the twisting wires have no effect on the wave impedances of a structure. The line asymmetry in a real cable can cause in the two-wire line a change of the wave impedance and a change of the input impedance.