Specifications

64 Chapter 8
Making Time-Gated Measurements
Gated Video Measurement (ESA)
Making Time-Gated Measurements
Gated Video Measurement (ESA)
This procedure utilizes gated video to gate the FM signal. For concept
and theory information about gated video see “How Time Gating
Works” on page 135.
Step 1. Set the ESA center frequency, span and reference level:
Press
FREQUENCY Channel, Center Freq, 40, MHz.
Press
SPAN X Scale, Span, 500, kHz.
Press
AMPLITUDE Y Scale, Ref Level, 0, dBm.
Step 2. Set analyzer sweep time to 2005 ms:
Press
Sweep, Sweep Time, 2005, ms.
For gated video, the calculated sweep time should be set to at least
to ensure that the gate is on at least
once during each of the 401 sweep points. In this example, the PRI is
5 ms, so you should set the sweep time to 401 times 5 ms, or 2005 ms. If
the sweep time is set too fast, some trace points may show values of
zero power or other incorrect low readings. If the trace seems
incomplete or erratic, try a longer sweep time.
NOTE Good practices for determining the minimum sweep time for
gated video:
In the event that the signal is not noisy, the sweep time can be set to
less than (as calculated above).
Instead of using PRI in the previous sweep time calculation, we can use
the “gate off time” where sweep time equals . In
our example we could use a sweep time of 401 points times 4 ms or
1.604 s. Increase the width of video bandwidth to improve the
probability of capturing the pulse using “gate off time”. If trace points
are still showing values of zero power, increase the sweep time by small
increments until there are no more dropouts.
Figure 8-5 Viewing the Pulsed-RF FM Signal (without gating)
# sweep points PRI (pulse repetition interval×)
# sweep points PRI (pulse repetition interval×)
# sweep points gate off time ×