By I. Switzer, P.Eng., Maclean-Hunter Cable TV Limited
Distortion in CATV amplifiers has been analyzed by several authors; notably Simons (1) who calculated the decibel relationships between various types of distortion products. Consideration of the practical implications of such an analysis leads to some potentially significant improvements in the subjective quality of television pictures transmitted through cable television systems subject to amplifier distortion. A reduction in the visibility of many third order distortion products is likely if the spacing 265 between adjacent visual carriers is properly controlled. A further improvement is likely to be obtained if all visual carriers are harmonics of a 6 MHz master oscillator. In such a case all second and third order distortion products are "zero-beat" and it is suggested that the subjective effect of interference in such a case would be substantially lower than is presently the case with present visual carrier frequency allocations.
The use of harmonic, coherent carriers will improve system performance and will also make possible some simplification of receiver tuners and converters.