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One might think that such a common term as signal-to-noise (S/N) ratio has only one definition, but this is unfortunately not the case. The definition depends upon what is meant by "signal" and what is meant by "noise" and these meanings determine how the measurement is made. To compare a National Cable Television Association (NCTA) S/N measurement made at VHF with an Electronics Industries Association (EIA) or International Radio Consultative Committee (CCIR) S/N measurement made at video baseband one must follow the vestigial sideband television signal through an ideal vestigial sideband demodulator. The resulting relationships show that there is only a small difference between the various definitions. Experimental results which back up the theoretical findings are described.