Subscriber loop feed apparatus
First Claim
1. In a telephone system, apparatus for applying DC power from a source and for coupling audio signals to and from a two wire loop having a nominal characteristic impedance, comprisingmeans for connecting said source of DC power to said two wire loop at its feed point, said means including first and second non-inductive resistance means connected respectively between one wire of said two wire loop and one pole of said source of DC power, the value of each of said resistance means being substantially equal to half of the resistive component of said nominal characteristic impedance,means for coupling audio signals to and from said two wire loop, said means presenting an impedance to said two wire loop dependent on the impedance presented to said coupling means,means, including DC blocking means, for connecting said two wire loop at its feed point to said coupling means,means for connecting audio signals to be applied to said two wire loop to said coupling means, said means presenting a high impedance to said coupling means, andmeans for transmitting from said coupling means audio signals received from said two wire loop, said means presenting a high impedance to said coupling means, whereby the loop matching impedance is determined principally by said non-inductive resistance means.
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Accused Products
Abstract
Telephone loop feed apparatus in which a hybrid couples audio signals to and from the subscriber loop and presents a high impedance to the loop relative to the loop impedance. DC power is coupled to the loop by matched resistors which determine the loop feed matching resistance. DC power is blocked from the hybrid to avoid saturation.
49 Citations
8 Claims
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1. In a telephone system, apparatus for applying DC power from a source and for coupling audio signals to and from a two wire loop having a nominal characteristic impedance, comprising
means for connecting said source of DC power to said two wire loop at its feed point, said means including first and second non-inductive resistance means connected respectively between one wire of said two wire loop and one pole of said source of DC power, the value of each of said resistance means being substantially equal to half of the resistive component of said nominal characteristic impedance, means for coupling audio signals to and from said two wire loop, said means presenting an impedance to said two wire loop dependent on the impedance presented to said coupling means, means, including DC blocking means, for connecting said two wire loop at its feed point to said coupling means, means for connecting audio signals to be applied to said two wire loop to said coupling means, said means presenting a high impedance to said coupling means, and means for transmitting from said coupling means audio signals received from said two wire loop, said means presenting a high impedance to said coupling means, whereby the loop matching impedance is determined principally by said non-inductive resistance means.
Specification