STERLING TELEPHONE AND ELECTRIC Co. Ltd
SINGLE LINE SECRET CONVERSATION INTERPHONES
MANY attempts have been made to design an Interphone System which will provide secrecy of conversation, that is, a System in which there is no induced cross talk and in which it is impossible for a conversation to be tapped by manipulation of the line selectors. Some of these systems have been very successful, but extremely costly, involving the use of specially constructed Telephones and expensive double wring.
Taking these and other points into careful consideration we have designed our Single Line Secret Conversation System which we have found entirely satisfactory for all practical purposes, and which can be offered at reasonable prices. In this System it is impossible to cut in on an engaged line, and as the talking circuit consists of the two Telephones connected in a metallic loop, the effects of induction are eliminated,
A means is provided by which the user can ascertain whether the station wanted is engaged on otherwise with out removing the Telephone from it's Switch Hook, thus avoiding the annoying waste of of time generally unavoidable with Interphone Systems.
The wiring is exactly similar to that of our ordinary "Primax" System except that the number of conductors required at the Cable is only two more than the total number of stations, and heavy extra leads for the battery are not required.
The Conductors should he not less than No. 20 S.W.G.
The Batteries required are two cells at each station for speaking and one common battery of four cell for ringing. These figures are for normal distances and may require to be varied in specific cases.
It is of great importance that the speaking batteries should be of high efficiency, and that they should be maintained in good condition. We therefore recommend "Invicta" Cells for this system, although our "Ceevox" Dry Cells can be used if preferred in consideration of first cost.
No. U 452
Automatic Single Line Secret Conversation Interphone. Wall Pattern ( Radial
Switch Type) comprising:
Metal Parts are Nickel Plated and Woodwork Solid Walnut.
Available for 10, 20 or 30 lines.
Taken from the Sterling Catalogue No. 11 & 12
Last revised: April 28, 2021