Abstract:
A coupler for attaching customer-owned equipment to the telephone network permits any customer signal below a prescribed signal level to pass without distortion or attenuation but linearly attenuates signals exceeding the prescribed level. The coupler measures the mean power of the customer''s signal and utilizes the results to switch the proper attenuating load across the line. The switch circuit of the coupler has a hysteresis characteristic to prevent distortion of the customer''s signal by repeated switching between different alternating modes when the customer''s signal has slight variations about the prescribed threshold level.
Abstract:
A time division multiplex system for use with subscriber stations utilizes a pilot tone to control switches which connect subscribers to the common line during designated portions of each cycle. The pilot tone taken from the line is changed in frequency before being used to control subscriber connection time to eliminate problems of feedback and crosstalk. Further, each subscriber station set is powered by the subscriber''s power during normal operation to further improve crosstalk performance. Service is maintained, however, if any subscriber''s power fails by reverting to line power and party line operation for the duration of the power failure. Private line service is automatically returned when subscriber power reappears.
Abstract:
A FREQUENCY MULTIPLYING CIRCUIT UTILIZES TRANSISTORS HAVING MATCHED CHARACTERISTIC TO ELIMINATE THE EFFECTS OF TEMPERATURE VARIATIONS. THE INPUT SIGNAL IS CONNECTED TO ONE TRANSISTOR OF A MATCHED PAIR OF TRANSISTORS HAVING IDENTICAL BIAS CIRCUITS. THE VOLTAGES OF THE EMITTER TERMINALS AND THE COLLECTOR TERMINALS OF THE TWO TRANSISTORS ARE RESPECTIVELY COMPARED AND COMBINED BY AN OUTPUT CIRCUIT. THE RESULTING OUTPUT SIGNAL CONTAINS FREQUENCY HARMONICS OF THE INPUT SIGNAL. TEMPERATURE EFFECTS ARE SUBSTANTIALLY CANCELLED IN THE VOLTAGE COMPARISON PROCESS AND THUS DO NOT AFFECT THE OUTPUT SIGNAL.
Abstract:
A telephone set equipped with a tone ringer includes an FM slope detector circuit and a following AM detector circuit. A difference amplifier receives outputs from a tone ringer signal amplifier and from the AM detector. The tone ringer thus serves a dual purpose as a ringer and as a speaker that is responsive to detected voice FM signals. The set may be employed for on-hook paging or emergency voice announcements.