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Phonopore and phonoplex F.D.M.telegraph systems used on railways in the late 19th century

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1 Author(s)
D. G. Tucker ; University of Birmingham, History of Technology, Faculty of Science & Engineering, Birmingham, UK

The phonopore and the phonoplex were both systems introduced in 1885 for providing additional telegraph channels (or, alternatively, in the phonopore system, a telephone channel) in the frequency range above that of the ordinary d.c. or Morse channels. The phonopore, developed by Charles Langdon-Davies in England, used a special kind of coupling transformer/condenser, which is here analysed but shown to have had few useful special properties, and used a `harmonic¿ telegraph channel, i.e. a keyed oscillatory signal. Edison's phonoplex used, for the highpass channel, signals derived from the transients produced by an induction coil. Both systems were made commercially, and had a certain success on railways. The Phonopore Syndicate (later Company) had an interesting but not successful history, here partially unravelled; from 1893, its managing director was C.E. Spagnoletti, F.R.S., Past-President of the Society of Telegraph Engineers, and newly-retired telegraph superintendent of the Great Western Railway. Although the company had, by 1895, raised around £100 000 of capital, it was in that year effectively purchased by the New Phonopore Telephone Co. for £2000. The new company continued in existence, with an issued capital reaching no more than about £8000, until it was purchased for £175 in 1916 by the Phonopore Construction Co., which finally ceased operations soon after 1920.

Published in:

Electrical Engineers, Proceedings of the Institution of  (Volume:121 ,  Issue: 12 )