Appendix, cont’d
VTG 400/400D • AppendixA-18
Phase anomalies of the burst manifest as a wavy appearance at the base of the
pulse region. Transmission line quality and length have more proportional effect
on the higher frequency pulse/burst combinations. Group delay effects may be
combated using a video processing amplifier or an equalizing network at the
termination end of the line.
PAL Multipulse
The 2T pulse is followed by a series of modulated pulses. (1) a 20T pulse
encompassing a 1 MHz sine wave burst, (2) a 12.5T pulse containing a 2 MHz
sine wave burst, (3) a 12.5T pulse containing a 4 MHz sine wave burst, (4) a
12.5T pulse containing a 4.43 MHz sine wave burst, and (5) a 12.5T pulse
containing a 5 MHz sine wave burst. Much like the multiburst signal discussed
earlier, each of these frequencies provides an intermediate bandwidth point for
consideration, including the color subcarrier and a frequency burst at the
bandwidth limit of the system.
The frequency burst inside each pulse is generated to fit within the pulse
symmetrically and have an amplitude which matches the pulse height and
duration without extending past its areal limits. Group delay in a television
distribution system will cause relative time shift between the imposed burst and
the encompassing pulse. Amplitude disturbance of the burst within each pulse
manifests as an upward or downward level shift, which appears as concaved
upward above black level (for low level) to convexed downward beyond black
(for excessive level). Phase anomalies of the burst manifest as a wavy
appearance at the base of the pulse region. Transmission line quality and length
will have more of a proportional effect on the higher frequency pulse/burst
combinations. Group delay effects may be combated using a video processing
amplifier or an equalizing network at the termination end of the line.
25. Transient Response
This pattern supports analysis of system transient response both
from black to white and white to black. Signal level transitions
from the extremes to middle gray require that the display system
response be carefully designed so that transition artifacts are not
visible on the gray background. Signal overshoot, undershoot, line distortion
(streaking), and ringing (trailing ghosts) manifest on the gray surround region
when system response is less than ideal.
The horizontal white and black bars emphasize lower frequency response issues.
Look for streaks trailing each of the horizontal bars. The short term vertical lines
represent high frequency transitions of time durations which will tend to show
up ringing problems within the high frequency response of the imaging system.
Ringing manifests as dark and light “ghosts” following the vertical lines and
bars in the test pattern.
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