Phase noise of oscillators such as local oscillators in modulators, receivers, set-top converters, etc., can introduce noise in TV pictures in a CATV system. Acceptable characteristics and the effects of phase noise are not recognized as readily as other more familiar and routinely measured distortions. The qualitative measure of phase noise is the perceptibility of phase noise in a TV picture. A quantitative measure is the baseband signal-to-noise ratio (SNR) and noise spectral density. This paper presents the theory relating the RF noise spectrum of an oscillator and the resulting video noise spectrum and SNR. Some representative data for oscillator noise in video modulators and set-top converters is given along with results of perceptibility tests.