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Abstract

A test object, such as a communication path used for data transmission, is examined by applying to its input a measuring signal M consisting of several simultaneously or sequentially generated test frequencies which may be harmonically interrelated, extracting from the output of the test object a distorted version E of the measuring signal, locally generating a compensation signal K with frequency components matching respective test frequencies, and subtracting the two signals E and K from each other to obtain a residual signal R=E-K. The compensation signal K is produced by one or more local oscillators and as many frequency converters under the control of regenerating circuitry which locks each of its components in phase and amplitude to the corresponding test frequency. Regeneration takes place in a different frequency range to which the residual signal R is transposed and from which the compensation signal K is retransposed with the aid of a locally generated carrier. Various transmission coefficients can be derived from the three signals R, E, K as well as from control voltages produced in the regenerating circuitry for the amplitude lock.

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First Claim