Alternating-current tests on high-speed telegraph cables

This paper is concerned with the alternating-current characteristics of loaded telegraph cables and their relation to transmission capacity. The general principles of transmission are reviewed, and by the use of periodic theory the performance which may be expected from a cable of given a.c. characteristics is estimated. Methods of testing are described by which complete data of the a.c. constants may be obtained during the process of manufacture. The effects of frequency, current, temperature and pressure are investigated, and the results of tests on the core for a long high-speed cable are discussed and used to estimate the performance of the cable when laid. Apparatus and alternative methods for testing the laid cable are detailed and a method of deducing the primary constants from attenuation and propagation-time tests is developed; values determined are compared with results of factory tests. Deductions regarding the value and regularity of the inductance loading are made from impedance tests. Departure and arrival curves for loaded cables are constructed from theory and compared with records obtained by test. Finally, the assumed criteria for satisfactory working, expressed in terms of attenuation, are verified by transmission tests.