METHOD OF AND APPARATUS FOR GENERATING A MULTITONE TEST SIGNAL

摘要

The invention consists in an apparatus for and a method of generating a test signal (T'), the method comprising the steps of generating at least first and second main signals (f1, f2), the first main signal having a frequency component at a first predetermined frequency, and the second main signal having a frequency component at a second predetermined frequency, combining said main signals to form a composite test signal (T') containing one or more intermodulation components, characterised in that the method further comprises the step of introducing at least one cancelling signal (2f1-f2, 2f2-f1) at a frequency substantially equal to that of one of the intermodulation components so as to suppress that intermodulation component in the composite signal. The cancelling signal may be combined with a main signal or the test signal, or may be introduced by modulating one of the main signals. The modulating signal (f2-f1) may be a composite modulating signal so as to generate two or more cancelling signals. Also, each of two or more main signals may be modulated by a respective modulating signal, or two main signals may be modulated by a modulating signal equal to the difference in frequency between them.