FAQs from Rohde & Schwarz

How to define Limit Lines with Steps and resulting Frequency Mismatches


I would like to define Limit Lines with steps. This does mean I would like to create a limit with two points at the same frequency. How make those cases clear for data reduction and final measurements based on the given limit?


This chapter describes what you should note when you define limit lines with steps.

Generally you can make those cases clear by not using the same frequency for both points at the limit line's step.

Rather you should shift one of these two points by e.g. 1 Hz or 10 Hz.

Of course the limit line still must comply with the details in the standard, which should explicitly describe the actual limit value at the frequency of the limit step.

Such a modification will not be visible in the graphics diagram, but you get clear conditions for calculating the margin values.

A similar approach should be applied for the definition of scan/sweep template subranges (start/stop frequencies) which are stringed together.

That prevents you from running into another dependency:

A test receiver may automatically adapt its measurement bandwidth at the frequency edges of the CISPR bands, when doing measurements with a CISPR detector.

As long as the frequency shift of a subrange border or of a limit line interpolation value is smaller than the scan/sweep frequency resolution, you should always still comply with the rules.

You may however see those shifted frequencies when listing the subranges or the limit line table in a report, although normally some kind of number rounding should make them look straight.