Figure 2-72 Spectrum Analyzer Display - Agilent Technologies 8560E User Manual

Making Measurements
Example 11: Time-Gated Measurement
Figure 2-72 Spectrum Analyzer Display
Notice that the gated spectrum is much cleaner than the ungated
spectrum. The spectrum you see is the same as would be seen if the
signal were on continually. To prove this, turn off the pulse modulation
in the signal generator by pressing ; the spectrum
SHIFT PULSE OFF
does not change. In both cases, you can see the two low-level
modulation sidebands caused by the narrow-band FM. Without gating,
these sidebands had been obscured by the pulse spectrum.
Using the Edge Mode and the Level Mode for
Triggering
Depending on the trigger signal that you are working with, you can
trigger the gate in one of two separate modes: edge or level. This
gate-trigger function is separate from the normal external trigger
capability of the spectrum analyzer, which initiates a sweep of a
measurement trace based on an external TTL signal.
Edge Mode
Edge mode lets you position the gate relative to either the rising or
falling edge of a TTL trigger signal. To trigger on the rising edge, press
, , so that EDGE is underlined,
SWEEP GATED VIDEO GATE CTL LVL EDGE
so that POS is underlined. With the equipment set
EDGE POL POS NEG
up as in the previous example, the oscilloscope screen should appear as
shown in Figure 2-73. By activating so that NEG is
EDGE POL POS NEG
underlined and decreasing the gate delay, the oscilloscope should
appear as shown in Figure 2-73, where the falling edge initiates the
gate delay.
Chapter 2 141