Telephone privacy device

Details Telephone privacy device Telephone privacy device

1975-03-31

1976-12-28

Claffy, Kathleen H.

179 18DA, 179 99, 179 39, H04M 168

Patent

active

040003760

ABSTRACT:
A privacy device for a telephone to prevent, unless desired, another telephone from being connected to the pair of incoming lines to which the telephone is connected. The privacy device employs voltage responsive means which is effective upon the telephone being connected to the incoming lines to establish a low impedance connection to the telephone only if the voltage across the incoming lines has initially at least a predetermined value. The low impedance connection drops the voltage across the incoming lines so that other telephones with the privacy device cannot be connected thereto. Means are provided for temporarily increasing the impedance across the lines to increase the voltage so that another telephone can be connected to the line when desired. This is done in a manner not to interrupt the connection between the lines but to maintain a minimum amount of current flowing therethrough so that the central office equipment does not detect an interruption in the line.
The privacy device is also equipped with means for turning it on regardless of the voltage across the lines when it is desired to use the telephone for intercommunication purposes within an office. When the intercommunication switch is pushed, the privacy device is caused to become conductive even though the value of the voltage across the lines is below the predetermined value.

REFERENCES:
patent: 2677018 (1954-04-01), Logan
patent: 2741667 (1956-04-01), Schweider et al.
patent: 2873316 (1959-02-01), Power
patent: 3035123 (1962-05-01), Nomura
patent: 3155776 (1964-11-01), Kawo et al.
patent: 3499121 (1970-03-01), McIntosh et al.
patent: 3530253 (1970-09-01), Bierman
patent: 3725601 (1973-04-01), Jetzt et al.
patent: 3760120 (1973-09-01), Moorehead
patent: 3860763 (1975-01-01), Sudon et al.
patent: 3961144 (1976-06-01), Hirate

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