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Abstract

A method and apparatus for measuring a characteristic of a communication signal modulated with a composite video signal without the need for a synchronizing device. Samples are taken of an intermediate signal derived from the received communication signal that represents the power spectrum of the communication signal at different instants of time. From a priori knowledge of the spectral characteristics of the communication signal modulated with a composite video signal, predetermined features of the communication signal are identified based on the relative values of the samples collected over a period of time equal to an entire frame of the composite video signal. The sample with the maximum value of a plurality of sample values collected for one frame is coincident with the occurrence of a vertical synchronization pulse of the composite video signal, which occurs when no modulation is present, and therefore is representative of the power of the communication signal at the visual carrier frequency. Once the sample with the maximum value sample is identified, the beginning of a frame is known, and therefore the power level of any other portion of the composite video signal can be measured based on the power level of the communication signal at a particular point in time with respect to the point in time that the maximum value sample occurred.

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First Claim