Specifications

126 Chapter 14
Demodulating and Viewing Television Signals (ESA-E Series Option B7B)
Measuring Depth of Modulation
Demodulatin
g
and Viewin
g
Television Signals (ESA-E Series
Option B7B)
Measuring Depth of Modulation
The depth of modulation provides a measure of the percentage of
amplitude modulation (AM) on the visual carrier. With Option B7B, the
analyzer can be used to measure the horizontal synchronization pulse
level and vertical interval test signal (VITS) white level on an
individual TV line from which a calculation of percent AM can be made.
Note that this measurement method will not be valid for some types of
scrambled video signals.
This procedure measures depth of modulation on an individual TV line.
For more information on TV trigger setup see the concepts chapter “TV
Trigger Setup Menu Functions” on page 154.
NOTE Before continuing, be sure you have performed the steps in
“Demodulating and Viewing Television Signals” on page 122 at the
beginning of the section to display a TV waveform with linear scaling.
Step 1. Trigger on a TV line that has a test signal containing the reference
white level within the waveform (100 IRE) such as the FCC, NTC-7 or
ITU Composite Test Signal (typically found at or near line 17 within
field 1 or field 2):
Press
Trig, TV, and enter a line number.
Step 2. Set the sweep time to 80 µs (option AYX or B7D required) to view a
complete TV line:
Press
Sweep, Sweep Time, 80, µs.
Step 3. Set the resolution bandwidth and the video bandwidth to 1 MHz:
Press
BW/Avg, Res BW, 1, MHz.
Press
BW/Avg, Video BW, 1, MHz.
Step 4. Turn on video averaging to 10 averages:
Press
BW/Avg, Average (On), 10, Enter.
This minimizes the waveform variations caused by the presence of
additional RF signals near the picture carrier, as well as waveform
noise or jitter.
Step 5. Enable a normal marker and using the front-panel knob move the
marker within the sync tip (NTSC or PAL waveforms) or the white level
(SECAM waveforms) at the top of the waveform:
Press
Marker, Normal, then rotate the front-panel knob (or press Peak
Search
).