Tektronix WFM 601i, Руководство пользователя

Страница: 98 / 135

Measurement Theory
3–20
WFM 601i Serial Component Monitor
from the appropriate targets. Figure 3-10 shows how the decoded color
difference signals draw the vector display commonly used throughout the
television industry.
Note that color burst is not shown in Figure 3-10. It would normally be shown at
180
°
on the B–Y axis for NTSC or
"
45
°
from the negative U axis for PAL.
Although this measurement technique originated with composite video signals,
there is a great deal of information about the component signals that can be
derived from vector displays. Not only can the encoder accuracy for both phase
and amplitude be checked, but some rough approximations about the relative
timing delays between the color difference signals can be made.
In the composite domain the transitions between the vector tips display timing
differences. But, because these timing differences include the delay in the
decoder output filtering they are largely ignored, unless they become too gross.
In the component domain there is no decoding required and therefore useful
information can be derived from the color bar transitions. These variations in
timing between the two color difference signals show up as looping or bowing of
the transitions. Theoretically, it would be possible to measure the amount of
bowing and convert the results to a delay value, but there are better methods
available. If the transition looping appears to be too much, use the lightning
display to determine the full amount of delay.
R
MG
Y
G
CY
B
R–Y OR V
B–Y OR U
Figure 3-10: Vector display relationship of the R–Y (V) and B–Y (U).
The electronic graticule for the WFM 601i provides vector targets that are
$
2%
of B–Y and R–Y amplitudes. This differs from composite vectorscope targets,
which are sectors indicating a polar, magnitude and phase error. These are the
errors most often caused by the coding, transmission and decoding of the