Abstract: A method for measuring the transmission characteristics of a transmission line during gaps in communications on said transmission line consists of monitoring the transmission line for a gap in communication thereon, and applying an identifier signal followed by a test pulse to the input of the transmission line when such a communications gap is recognized. An output of the transmission line is monitored and when the identifier signal is recognized, the test pulse which follows the identifier is evaluated. The test pulse is made up of a plurality of component frequencies at equally spaced intervals, and evaluation of the test pulse at the output yields the attenuation of phase characteristics of the transmission line for each component frequency, without interfering with communications on the line.

Abstract: Cross-talk attenuation characteristics and/or other transmission characteristics are measured by means of a method which applies a test pulse to the input of an object under test, the test pulse being composed of a plurality of component frequencies having predetermined amplitudes and initial phase angles, with the output of the test object being evaluated by means of Fourier analysis, using an FFT processor. The effective noise is substantially reduced by transmitting plural test pulses, and calculating the mean value of plural results produced sequentially by the FFT processor. Alternatively, the effective noise is reduced by reducing the widths of the effective pass bands of the evaluation by carrying on the evaluation over a period which exceeds the period of a single test pulse, or by setting the amplitudes of some components of the test pulse to zero and increasing the amplitudes of the remaining components.