Importance

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Abstract

A method and apparatus for measuring a change in the insertion loss of a transmission line in a communication system is disclosed. The method provides feeder cable insertion loss detection in a transmission system without interfering with normal operation. The method includes injecting a non-interfering signal at a predetermined frequency onto a cable providing normal operating signals to a narrowband device at a predetermined frequency, measuring the amplitude of the injected signal, measuring the amplitude of a reflected signal, the injected signal being reflected by the narrowband device and processing the amplitude of the injected signal and the amplitude of the reflected signal to derive a current insertion loss for the cable. In addition, the method further includes comparing the current insertion loss to a prior insertion loss and determining the cable to be defective when the current insertion loss differs from the prior insertion loss by a predetermined amount and replacing the cable when the current insertion loss differs from the prior insertion loss by the predetermined amount. The injecting further includes selecting a signal for injection having a frequency and power that does not interfere with the normal operating signals and which causes the signal to reflect back from the narrowband device. The frequency of the selected signal for injection causes the narrowband device to appear to the selected signal for injection as a short or an open. The narrowband device is an antenna, a low noise amplifier, a power amplifier, a filter or a RF-to-light converter for a fiber optic distribution network.

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First Claim