Reflections in a coaxial cable due to impedance irregularities. An Experimental Study of the Correlation between Steady-State and Transient Measurements

The first part of the paper outlines the significance of impedance irregularities in a coaxial cable and develops the relations between the actual irregularities, the curve of input impedance against fre quency, and the echo response of the cable to a voltage impulse. The steady-state and transient methods of measurement are then compared theoretically, on the basis of resolving power, and are found to lead to the same result. These theoretical conclusions are proved experimentally by measure ments on an artificially faulty cable. Suggestions are made for the application of these results to factory production of cables; in particular the statistical aspect is considered and parameters giving the maximum correlation are discussed. A simple pulse-testing method, using two spaced pulses, is then described with particular reference to the testing of factory lengths of cable intended for television transmission. Although the results described in this paper are taken from work carried out between 1945 and 1948 the matter is still one of practical interest to manufacturers and users of cables and to all who are concerned with long-distance coaxial-cable transmission problems.