Qualifying a telephone line for digital transmission service

Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal

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379 6, 379 24, 379 26, 379 32, 324519, 324525, 324527, H04M 124, H04M 308, H04M 322

Patent

active

060849460

ABSTRACT:
A telephone wire pair is qualified for digital signal transmission by central office testing. The tip-to-ring capacitance of the wire pair is measured while applying an test signal in the 20-30 Hz range to the wire pair. The tip-to-ring capacitance is used to compute a first length, and the first length is compared to a pre-determined length. If the first length exceeds the pre-determined length, then the wire pair is qualified based upon another comparison of the measured capacitance to a pre-determined capacitance. On the other hand, the first length is less than the pre-determined length, the tip-to-ring capacitance is measured at a frequency of, preferably, 600 Hz. The test signal at this frequency minimizes errors due to resistive and inductive components of the primary constants of the wire pair and/or a ringing device connected to the wire pair. A final comparison between the pre-determined capacitance and the measured capacitance at the higher frequency determines whether or not the pair qualifies for digital transmission.

REFERENCES:
patent: 4862492 (1989-08-01), Zwick
patent: 5347225 (1994-09-01), Graham
patent: 5864602 (1999-01-01), Needle
patent: 5978449 (1999-11-01), Needle

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