Which modulation method is used for color signals in the headend?

Which modulation method is used for color signals in the headend?

• A. Amplitude and phase modulation
• B. Frequency modulation
• C. Amplitude modulation
• D. Phase modulation

Answer: (A)

Color information is carried on the chrominance subcarrier using a two-dimensional modulation that varies both how strong the signal is (amplitude) and where its phase is pointing. This is Quadrature Amplitude Modulation, where two color-difference components (often described as I and Q) are encoded by modulating the subcarrier in quadrature (90 degrees apart). Because chroma requires conveying two independent pieces of information, changing both amplitude and phase is necessary to fit all color data into the channel bandwidth. If you used only frequency modulation, or only amplitude or only phase modulation, you wouldn’t be able to represent the two color components simultaneously. So combining amplitude and phase modulation is what makes color signals in the headend work correctly.

Color information is carried on the chrominance subcarrier using a two-dimensional modulation that varies both how strong the signal is (amplitude) and where its phase is pointing. This is Quadrature Amplitude Modulation, where two color-difference components (often described as I and Q) are encoded by modulating the subcarrier in quadrature (90 degrees apart). Because chroma requires conveying two independent pieces of information, changing both amplitude and phase is necessary to fit all color data into the channel bandwidth. If you used only frequency modulation, or only amplitude or only phase modulation, you wouldn’t be able to represent the two color components simultaneously. So combining amplitude and phase modulation is what makes color signals in the headend work correctly.