Security line card circuit for key telephone system

Details Security line card circuit for key telephone system Security line card circuit for key telephone system

H - Electricity

04

M

379/33, 379/57,

H04M 1/68 (2006.01) H04M 3/22 (2006.01) H04M 9/00 (2006.01)

Patent

CA 1043916

ABSTRACT OF THE DISCLOSURE To prevent clandestine listening devices located in a key telephone subscriber station from utilizing the tip and ring leads of the subscriber station as a transmission path out of the subscriber's building, the subscriber station tip and ring leads are open circuited at the line card circuit during an on-hook or hold condition. Besides isolating the tip and ring leads from the subscriber station during hold and on-hook, the security line card circuit prevents high frequency signals from propogating down the telephone line when the subscriber station is on-hook. The security line card circuit allows the sub- scriber to exercise full supervisory control over the telephone lines and includes circuitry that controls the operation of audible and visual indicators of the associated key telephone.

239240

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