Service manual

STP 11-25R13-SM-TG
S - 18
Section VI. THE NTSC COLOR TELEVISION SYSTEM
S-18. General.
The NTSC is a research group set up by the leading equipment manufacturers and broadcasters.
The NTSC examines all aspects of television, such as frequency, bandwidth, quality, power, color and
method of transmission.
a. A review of the standard bandwidth breakdown of a TV channel is presented now so that you
can associate it with the bandwidth of the color signal when it is presented later (see Figure S-17).
(1) Bandwidth is 6 MHz.
(2) Video carrier is 1.25 MHz above the vestigial sideband.
(3) The sound carrier is 4.5 MHz above the video carrier.
(4) Video information must be compressed within the 4.2 MHz band above the video carrier.
Figure S-17. TV Bandwidth
S-19. Frequency Interleaving.
The color information must be contained within the same 4 MHz band as the monochrome signal.
How is this done? The answer is to be found in the nature of the television signal. The fact was
discovered as far back as 1929 that a monochrome 4 MHz video signal does not occupy every cycle of
the 4 MHz assigned to it. Rather, this signal appears as clusters or bursts of energy located about the
harmonics of the 15,750 Hz lines scanning frequency.
a. Figure S-18 indicates that in a TV scene, the electrical signal (that is, the repetitious line signal)
consists of bursts of signal energy at the line harmonics with harmonics of 30 (frame rate) and 60 (field
rate) Hz 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 S-18 it can be seen that half of the
video spectrum is unused.