a. The color information is contained within the same 4.2 MHz band as the
monochrome signal. It was discovered that a monochrome 4 MHz video signal does not
occupy every cycle of the 4 MHz assigned to it.
Rather, this signal appears in
forms of clusters or "bursts" of energy located in harmonics of the 15750 Hz line-
scanning frequency.
b. Figure 1-13 indicates that in a TV scene, the electrical signal consists of
bursts of signal energy at the line harmonics with harmonics of 30 Hz (frame rate)
and 60 Hz (field rate) clustered on either side. Other frequencies are attenuated
so much that the space in between is considered to be unoccupied by any electrical
signal. From Figure 1-13 it can be seen that half of the video spectrum is unused.
Since the scanning rate for the chrominance and for the luminance signals are the
same, the concentrations of energy produced by both are spaced at the same
intervals. It is feasible, therefore, that the bands of concentrated energy of the
chrominance signal could be spaced between the bands of the luminance signal. As
seen in Figure 1-13, the spaces in the frequency occur at odd multiples of one-half
the line frequency.
Figure 1-13.
Distribution of energy in the frequency spectrum of
a standard monochrome signal
c. If a subcarrier frequency equal to an odd multiple of one-half the line
scanning frequency is chosen, the chrominance and luminance signals are
interleaved. This practice is followed today (fig 1-14).
5. Color signal components.
A color signal consists of two components; a
monochrome signal and the signal which carries information concerning color. Each
component will be examined separately.
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