Qualifying telephone line for digital transmission service
First Claim
Patent Images
1. A method of qualifying a telephone wire pair for digital signal transmission, the wire pair consisting of a tip connection and a ring connection, the method comprising the steps of:
- applying an AC test signal to said wire pair, said AC test signal at a frequency greater than 200 Hz; and
measuring tip-to-ring capacitance of said wire pair by using the applied AC test signal at said frequency greater than 200 Hz.
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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 to the wire pair an AC test signal at 600 Hz. The test signal at this frequency minimizes errors due to line inductance and/or a ringing device connected to the wire pair. Reliable measurement of the length of the wire pair is achieved. Flaws in cable sheathing can also be detected based on measurement of tip-to-ground capacitance and/or ring-to-ground capacitance.
100 Citations
22 Claims
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1. A method of qualifying a telephone wire pair for digital signal transmission, the wire pair consisting of a tip connection and a ring connection, the method comprising the steps of:
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applying an AC test signal to said wire pair, said AC test signal at a frequency greater than 200 Hz; and measuring tip-to-ring capacitance of said wire pair by using the applied AC test signal at said frequency greater than 200 Hz. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Telephone cable test apparatus for estimating an effective length of a telephone wire pair, the wire pair consisting of a tip connection and a ring connection, the apparatus comprising:
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generating means for generating an AC test signal at a frequency greater than 200 Hz; means for applying to said wire pair said AC test signal generated by said generating means; and means for measuring tip-to-ring capacitance of said wire pair by using said AC test signal applied to said wire pair. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of detecting flaws in a telephone cable sheath, said sheath containing a plurality of twisted wire pairs each made up of a tip connection and a ring connection, the method comprising the steps of:
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selecting one of said twisted wire pairs contained in said telephone cable sheath; estimating a length of said sheath by first measuring tip-to-ring capacitance of said selected twisted wire pair; second measuring at least one of tip-to-ground (T-G) capacitance and ring-to-ground (R-G) capacitance with respect to the selected twisted wire pair; determining an expected T-G or R-G capacitance based on said estimated length of said sheath; and comparing said measured T-G or R-G capacitance with said expected T-G or R-G capacitance. - View Dependent Claims (21, 22)
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Specification