# How Analogue Colour Televisions Works: the Coding and Decoding Process Show Video

it must have a frequency that ensures the chroma nut signal occupies the frequency space between the luminance horizontal spectral lines and this could be achieved by making the subcarrier frequency an odd multiple of half the horizontal frequency so the subcarrier frequency FSC is 455 times 15.734 kilohertz divided by 2 which is equal to 3.579545 megahertz in conventional amplitude modulation the signal modulates the subcarrier as shown the frequency spectrum of the amplitude modulated signal is then shown on the right hand side of the picture the Spectrum consists of the subcarrier frequency and the sidebands that contain signal information the problem with using this is the sub carrier frequency could appear as a pattern on the luminance signal ntsc uses suppressed carrier quadrature modulation in this technique the subcarrier is suppressed so that the Spectrum just contains the color information in the side bands and thus the interference to the lunar signal is minimized this diagram shows a luminance signal Y and the two color different signals R minus y and B minus y for a line of a color bar image these signals now need to be modulated onto the subcarrier to create the chrominant signal in the ntsc system the r minus y and B minus y signals are used to modulate the subcarrier using a circuit known as a balanced modulator which suppresses the subcarrier and so the resulting output from each modulator consists of the sidebands that contain the color information for the B minus y signal the subcarrier is shifted in Phase by 90 degrees compared to the r minus y signal the two signals are then combined and the result is called the chrominant signal the complete ntsc coder takes the red green and blue signals and adds them together in The Matrix circuit to create the luminant signal y it also produces the r minus y and B minus y signals which are fed to the balance modulators to create the chrominant signal as previously explained the chrominants and lumina signals are then combined to form the composite video signal this diagram shows the B minus y voltage for the color bars below this is the sub carrier and below this is the output from the balance modulator you can see that there's no output when there's no color information for example when the color bar is white or black you can also see the phase changes as the color bars change it is easier to understand the chronic signal than the vector diagram is shown the color sub carrier carries the color in two ways the vector diagram shows all possible positions of the color Vector representing an individual color any one of which is related to the phase is the unmodulated sub carrier the saturation of the color I.E the