Learning Event 3:
DEFINE AND DESCRIBE THE ENCODER
1.
Encoder: The encoder produces a composite color television signal from
the various individual signals originating in a color television system.
The complex circuits of the unit perform the following essential functions
necessary for transmission of the TV signal according to the FCC
specifications:
a. Cross-mixing or matrixing is taking the red, blue, and green video
signals from a color TV camera chain, for a color slide camera or from a
color bar generator, in proper proportion to produce a luminance signal in
the three tube system to produce a two-color difference or chrominance
signal.
b. Filter the chrominance signals to maintain their required bandwidth.
c. Compensates for delays in the signals introduced by filtering the
chrominance signals.
d. Amplitude and phase modulate the color difference signal.
e. Add E1A sync signals to the video and color information.
f. Produce a burst signal for color synchronization.
g. Shift phase of incoming 3.58 MHz subcarrier through 360 degrees to
allow matching of several encoder outputs with respect to subcarriers phase.
h. Maintain carrier balance automatically.
2.
The essential circuits of an encoder are basically a matrix and delay,
modulator, burst generator, and an adder circuit. In the matrix and filter
section, the red, green and blue signals are fed to the unit. There they
are transformed to a luminance (Y), and two color-difference (I and Q)
signals which are then adjusted with respect to bandwidth and delay.
a. In the modulator section, the two color difference signals are
modulated in phase and amplitude to form the chrominance signal. Burst flag
is formed and/or processed and used to key the color sync burst into the
composite output.
b. In the adder circuit, the operation needed to produce a composite
signal from the chrominance, luminance and synchronizing signals is
accomplished.
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