1974-11-27
1976-12-14
Claffy, Kathleen H.
179 81E, H04M 168
Patent
active
039977374
ABSTRACT:
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 propagating down the telephone line when the subscriber station is on-hook. The security line card circuit allows the subscriber 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.
REFERENCES:
patent: 2975237 (1961-03-01), Abbott
patent: 3126452 (1964-03-01), Pettersson
patent: 3372236 (1968-03-01), Schwartz
patent: 3614334 (1971-10-01), Bonvallet
patent: 3629514 (1971-12-01), Flamini, Jr.
patent: 3703611 (1972-11-01), Kiyomiya et al.
patent: 3715514 (1973-02-01), Bell, Jr.
patent: 3758729 (1973-09-01), Everhart
Claffy Kathleen H.
Myers Randall P.
San/Bar Corporation
LandOfFree
Security line card circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Security line card circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Security line card circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1346081