Television signal-to-noise ratio before and after demodulation

The reception of amplitude-modulated television signals is considered, under noise-limited conditions where the signal-to-noise ratio of the demodulated signal is controlled by the noise figure of the receiving equipment. The magnitude of the `demodulation factor¿, relating the signal-to-noise ratio on carrier to that at video frequency after demodulation, is discussed. It is concluded, from experimental evidence, and from consideration of the demodulation process, that for system I the value of the factor lies close to 3 dB.