Service manual

STP 11-25R13-SM-TG
S - 25
i. The readjustment of chrominance signal phases is called high definition color transmission and
is the system of color transmission used today. Since the chrominance axis in this system is not the
same as R-Y and B-Y, they have been given new titles. One is called the I signal since it is nearest in-
phase to the burst or the reference subcarrier; the other is called the Q signal since it is in quadrature with
the I signal.
j. Figure S-23 is a vector diagram of the I and Q color coordinates and their relationship to the old
R-Y/B-Y system. The I and Q signals are produced with their phase coordinates 90 degrees from each
other. The +1 signal is 57 degrees from the reference subcarrier, with -1 at 237 degrees (180 degrees)
from +I. The +Q signal is displaced 57 degrees (+90 degrees), or 147 degrees from the reference
subcarrier, with the -Q signal 180 degrees from it, or 327 degrees from the reference subcarrier.
Figure S-23. Vector Diagram
S-22. Formation of the Y, I, and Q Signals.
Color transmission begins at the camera where the light of the original scene is separated into three
primary colors: red, green, and blue. Three individual signals or electrical elements are provided by
means of three pickup tubes to represent the information of the three primary colors. The three electrical
signals representing the red, green, and blue hues of the televised scene are then routed to a device
known as an encoder (also referred to as a colorplexer in older equipment).
a. Encoders are sometimes referred to as the heart of the television system. This unit combines
the various individual signals originating at the camera into a composite color television signal. Figure
S-24 shows a typical encoder. As can be seen, the red, blue, and signals from the camera enter the
encoder and are fed to the matrix section.