Specifications

Operation
VTM-200 Installation and Operation Handbook 3-4
Making Digital Video Measurements with the VTM-200
The VTM-200 monitors analog NTSC/PAL composite and serial component digital
video.
Video adhering to the ITU-R BT.601/SMPTE 259 standards consists of three
component channels multiplexed into a single data stream. The three components are
luminance (or "Y") and two color difference signals (C
B
and C
R
). The color difference
signals are similar to the more familiar analog color difference components B-Y and
R-Y. The significant difference is in amplitude scaling, which leads to an important
point to remember when measuring serial component digital signals: All three
components of a 100% signal will have the same maximum peak to peak
amplitude. The VTM-200 graticule shows this maximum legal excursion as 0 volt to
+0.7 volt. For example, a 100% color bar signal with a white flag will have all three
components (Y, C
B
, and C
R
), ranging from 0V to +0.7 V. Y channel blanking level is
0 volt, and both C
B
and C
R
blanking levels are 0.35 volt. If a 75% signal with a 100%
white bar is viewed on the VTM-200, the Y channel will still range from 0 to +0.7 volt,
since the 75% refers to color saturation. In this case, peak-to-peak excursion for the C
B
and C
R
channels will now be 75% of 0.7 volt, or 0.525 volt peak-to-peak. This range is
centered on blanking level (0.35 volt), so the maximum excursion of C
B
and C
R
with
75% saturation is 0.0875 volt to 0.6125 volt. These are the only peak-to-peak
excursions for the color difference channels; there are not the range of standards with
serial component digital video that there are with analog component (Beta, MII, EBU,
SMPTE, etc.). Amplitudes are the same in both 50 Hz and 60 Hz serial component
digital video.
Another difference between viewing analog and digital component video is the
blanking portion of the signals. Unlike analog, a digital component has no sync pulse
or other synchronizing portion of the signal. There are synchronizing data words at the
beginning and end of blanking, but these do not look like sync pulses. Only the active
video portion of the signal is displayed on the VTM-200, but this is precisely
controlled so that timing measurements can be made relative to the first displayed
pixel. The first displayed pixel is the first active video sample after SAV (Start of
Active Video - the synchronizing words that appear at the end of blanking). A SETUP
menu item allows for the display or blanking of spikes representing the SAV and EAV
(End of Active Video) that indicate the beginning and end of each component.
The graticule scales change when displaying waveforms as RGB or composite signals.
The RGB display is useful for gamut checking—any portion of the signal that
extends more negative that 0 volts or more positive than +0.7 volts in a RGB
display is invalid and the cause of a GAMUT error. Displaying an input as a
composite signal is a quick check of its suitability for encoding. Still, 100% saturated
signals will not encode properly. A quick check when displaying a composite wave-
form is to examine whether the chrominance extends above or below the luminance
limits. Remember, the peak luminance for 60 Hz signals is 0.714 volt, slightly
above the 0.7 volt graticule line.