Datasheet

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APPLICATION NOTEInterference Hunting
The spectrogram measurement is designed to address this
type of problem. Like the spectrum display it will show low
frequency on the left-hand side, and higher frequencies on the
right-hand side. Unlike a basic spectrum display, color is used
to represent amplitude, and all of this information is plotted
versus time on the y-axis. The spectrogram is effectively a strip
chart recorder showing the spectrum activity over time.
In a swept tuned analyzer this spectrogram will be disjointed
in time as the instrument is sweeping. The SA sweeps through
frequency meaning that trace points on the left side of the span
occur at earlier times than trace points on the right. As such,
there can be no timing relationships within a spectrogram
captured by a swept analyzer. A spectrogram created by a
RTSA is comprised of continuously recorded spectrum data
without sweeping.
The RTSA has the added benefit of complete domain
correlation, so information in the spectrogram can be directly
correlated with other measurements (i.e. modulation, power,
CCDF). This means that the RTSA is able to characterize time-
varying events in the spectrum, including the signatures of
transient RF signals.
Unattended monitoring
A useful way to find unexpected signals is by unattended mask
monitoring. When RF systems are being compromised with
interference it’s often time consuming to manually monitor
the spectrum waiting for something to happen. Mask Search,
a function built into SignalVu-PC, allows users to create a
graphical mask around their frequency of interest and then
trigger an action when the mask is violated.
Mask Search provides a number of trigger mechanisms:
• Signal > pre-defined level – this lets the user setup a
detection threshold for a signal
• Signal < pre-defined level – this provides a RF drop-out
trigger
• Signal inside a Mask – this provides a container to hold a
signal
• Signal outside a Mask – this provides a shield around a
signal
FIGURE 7. A real-time spectrogram lets you record data for hours and find
signals that otherwise could be missed.
FIGURE 6. The spectrogram shows how an RF signal changes over time.