302 N5511A Phase Noise Test System User’s GuideEvaluating Your Measurement ResultsProblem SolvingProblem SolvingDiscontinuity in the graphBecause noise distribution is continuous, a break in the graph is evidence of ameasurement problem. Discontinuity in the graph will normally appear at thesweep-segment connections.Table 14-2 identifies the circumstances that can cause discontinuity in thegraph.Table 14-1 List of topics that discuss problem solving in this chapterIf you need to know: Refer To:What to do about breaks in the noise graph Discontinuity in the GraphHow to verify a noise level that is higher than expected High Noise LevelHow to verify unexpected spurs on the graph Spurs on the GraphHow to interpret noise above the small angle line Small Angle LineTable 14-2 Potential causes of discontinuity in the graphCircumstance Description Recommended ActionBreak between segments whereclosely spaced spurs are resolved inone segment but not in the next.Closely spaced spurs that are resolved inone sweep-segment but not in the next cancause an apparent jump in the noise wherethey are not resolved.Use the Real-time Monitor toevaluate the noise spectrum at thebreak frequency on the graph. Toeliminate the break in the graph, youmay find it necessary to change theSweep-Segment Ranges so that themeasurement resolution remainsconstant over the frequency rangewhere the spurs are located.Erratic Noise: One or more segmentsout of line with the rest of the graph.This occurs when the noise level of thesource being used is inconsistent over time.The time-varying noise level causes theoverall noise present when one segment isbeing measured to differ from the levelpresent during the period when the nextsegment is measured.Repeat the noise measurementseveral times for the segment thatdoes not match the rest of thegraph, and check for a change in itsoverall noise level.
