An improved noise loading arrangement and method are disclosed capable of measuring low intensity intermodulation distortion products, such as introduced in the operation of individual wideband transmission repeaters. The improved arrangement and method also have the further capability of resolving individual orders of distortion products. The arrangement utilizes a noise signal generator that produces a pseudorandom signal made of several spectral components providing high spectral density throughout a large bandwidth to simulate a broadband message load obtained by frequency multiplexing several independent signal sources. The noise signal is shifted in frequency before a quiet band is produced in the signal applied to the transmission apparatus to be tested. The orders of intermodulation distortion products appearing in the quiet band of the output signal of the transmission apparatus are individually measured to evaluate same. Automation of the test sequence is provided by a computer which acts as a general controller. The computer also processes the test data obtained by using a conventional signal averaging technique.
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