The Twisted Pair Telephone Transmisson Line

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  • Author: Richard LAO
Telephone line is abalanced twisted-pair transmission line, and like any electro-magnetic transmission line, its characteristic impedance Z 0 can be cal-culated from manufactur-ers’ data and measured on an instrument such as the Agilent 4395A (formerly Hewlett-Packard HP4395A) net-work analyzer. For lowest bit-error-rate (BER), central office and customer premise equipment should have analog front-end cir-cuitry that matches the telephone line impedance. This article contains a brief math- ematical derivation and and a computer pro-gram to generate a graph of characteristic impedance as a function of frequency.