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Making Measurements Using Spectrum Analyzer Mode
Using the Time-Gated Spectrum Analyzer Capability Without the Gate Utility (Option 107 only]
Introducing
the
Time-Gated
Spectrum
Analyzer
Capability
As the spectrum analyzer takes a measurement sweep, it displays a specific
frequency as it sweeps across the frequency range of the spectrum analyzer.
Since signals can vary in tune, the spectrum analyzer can miss an event
at one frequency because it is sweeping at a different frequency when the
event occurs. With the time-gated spectrum analyzer capability, the spectrum
analyzer can provide a “window” of what is going on with a signal at any
specific tune, since the analyzer has the capability to selectively acquire data
based on an external trigger signal. The “window” represents a periodic
timed event during which data acquisition is enabled.
The following figures demonstrate how the time gate can be used to view a
signal. For example, you could have two signals at the same frequency in
alternating tune slots so they can share a common system. You can use an
oscilloscope to determine whether there are two signals (see Figure 5-16).
However, you could not use a standard spectrum analyzer since both
signals would contribute to the displayed frequency spectrum. By using the
time-gate functions, you can use a spectrum analyzer to mask out one signal
at a time and measure each of the two signals separately. (See Figure 5-17.)
NOTE
When the time-gated spectrum analyzer capability is enabled, it interrupts the internal signal path of
the spectrum analyzer, so several spectrum analyzer functions may not be available under all conditions.
These conditions include: marker noise
IMK
BOISE
OM
OFF
1,
sample detection while in the
frequency span mode, and AM/FM demodulation and TV sync trigger. The marker counter function
IMK
COUNT ON OFF
I
is not directly affected by the operation of the time-gated spectrum
analyzer capability, but many signals that are appropriate for time-gating
(for
example, pulsed RF
signals) will not be counted correctly by the marker counter function.
5-34