R&S FSH
Spectrum Analyzer Mode
Configuring Spectrum Measurements
Operating Manual 1173.6275.12 - 30
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3.2.8 Using Limit Lines
Limit lines help you to identify if a signal complies with certain level characteristics.
A limit line is made up out of two or more points that are connected to a line. Each of
the points that define the shape of the limit line consists of two coordinates. One
coordinate defines the horizontal position (e.g. frequency), the other one the vertical
position. With the R&S FSH you can build limit lines that consist of up to 1000 points.
Values that define the horizontal characteristics of the limit line can be either absolute
values (e.g. frequency in MHz) or relative values whose reference is the center of the
measurement trace (e.g. the center frequency). Relative values are of advantage if
you, for example, measure modulated output signals and you change the center
frequency but need the limit line to remain the same. Absolute limit lines have the file
extension ".abslim" while relative limit lines have the file extension ".rellim"
Values that define the vertical characteristsics are always level values in dB. If the
scaling of the vertical axis is currently a linear one (units V or W), the R&S FSH
automatically switches to a logarithmic scaling after you turn on the limit line.
After turning on a limit line, the R&S FSH checks if the signal violates the shape of the
limit line. If one or more signal levels exceed the limit value, the R&S FSH features
several indicators that the limit check has failed.
● A general message in the diagram header that indicates if the signal violates the
limit line, including the trace that violates the limit:
● An audio signal that sounds every time a limit is violated
● The trace color turns red in areas of the spectrum that violate a limit
You can create and edit limit lines with the R&S FSH4View software package and then
transfer them into the internal memory of the R&S FSH. The number of limit lines you
can store in the memory depends on other datasets available on the R&S FSH or, if
you are using an external storage device (e.g. memory stick), the size of it.
For more information see "
3.2.8.1 Selecting a Limit Line
Before selecting a limit line, you need to decide if you want to use it as an upper or
lower limit line. In case of upper limit lines, the R&S FSH checks if the signal is above
the limit line. In case of lower limit lines, the R&S FSH checks if the signal is below the
limit line.
You also have to make sure that the limit line is compatible to the scale of the
horizontal axis.
► Press the LINES key.
► Depending on the application, press the "Upper Limit" or "Lower Limit" softkey.
The R&S FSH opens a dialog box to select the limit line.
► Select the "Load From File…" menu item.
► Press the "Sort/Show" softkey.
