Skip to Main Content
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 `harmonicÂ¿ 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 Â£100 000 of capital, it was in that year effectively purchased by the New Phonopore Telephone Co. for Â£2000. The new company continued in existence, with an issued capital reaching no more than about Â£8000, until it was purchased for Â£175 in 1916 by the Phonopore Construction Co., which finally ceased operations soon after 1920.