Time-Domain Reflectometer

A method of time domain reflectometry comprising:

• transmitting a test signal through at least one line feed resistor to the ends of an electrical cable under test;
• receiving a line signal from the cable at those ends;
• and
• filtering the line signal to enhance a portion of the signal indicative of any fault on the cable by balancing the signal according to the electrical characteristics of a normal cable of the same type as the cable under test, by applying a filter function, to generate and output a filtered signal.

A time domain reflectometer for testing an electrical cable, comprising:

• test signal generator means;
• at least one line feed resistor means, connected between the test signal generator means and a pair of terminals, for connection to the ends of an electrical cable under test;
• and
• a means for processing signals, connected to the terminals, to receive a line signal including a reflection of a test signal transmitted into the cable under test,
• wherein the means for processing signals is programmed to filter the line signal to enhance a portion of the signal indicative of any fault on the cable by balancing the signal according to the electrical characteristics of a normal cable of the same type as the cable under test, by applying a filter function:
• 1+Rf.Y(s) to the reflected signal, where Rf is the resistance of the feed resistor, and Y(s) is an estimate of the input admittance of the transmission line, s being the Laplace variable, and acquiring at least one estimate of Y(s) from known or estimated electrical characteristics of the cable under test selected from the variables:
• C, the distributed line capacitance per unit length
• L, the distributed line inductance per unit length
• R, the distributed line resistance per unit length and
• G, the distributed line conductance per unit length
• or functions of these variables,
• in the equation for input admittance in the Laplace domain:
• Y(s)=√((sC+G)/(sL+R)).