About Frequency

The parameters on the Frequency tab are used to configure the frequency parameters for a measurement.

Depending on whether the Show Center/Span check box is selected or cleared, frequency parameters in the Frequency tab and X-axis annotation on traces are expressed in terms of either:

Center and Span: X-axis is annotated with Center and Span.

Start and Stop: X-axis is annotated with Start and Stop frequencies.

Full span measurements view the entire available frequency spectrum on one display. Alternately, smaller slices of the frequency spectrum may be viewed.

Any number of different spans can be selected and positioned by specifying their start and stop frequencies or by specifying a center frequency and span size.

Changing one parameter causes other parameters to change. For example, changing start causes span and center to change. The following table shows how Start, Stop, Center, and Span interact:

If changed...	affects these...	Does not affect
Start	Span & Center Time Data (changes to Zoom mode)	Stop
Stop	Span & Center	Start
Center	Start & Stop	Span
Span	Start & Stop Time Data (changes to Zoom mode)	Center

An exception occurs when changing one parameter would set another to an invalid value. For example, if the Center Frequency is changed so that with the current Span the Start Frequency would be less than 0, the VSA adjusts the Span so that the Start Frequency is valid.