Why don't the Measure at Marker or Auto Measure peak detector values match the peak trace marker values on my EMC analyzer?
Two problems have been found that could cause the results of both the "Measure at Marker" and "Auto Measure" routines to be incorrect:
- A problem where the EMI Detector Auto-Ranging operation results in an incorrect setting of the reference level; yielding signals that are significantly above the top graticule and beyond the measurement range of the instrument. The Auto-Ranging operation is automatically invoked when either the Quasi-Peak or EMI Average detectors are selected during both the "Measure at Marker" or "Auto Measure" routines, and thus could affect the measurement results.
This can only be seen with signal levels greater than approx. 45dBuV that are four divisions or more from the top graticule on-screen before making the measurements.
- A problem where E7403A, E7404A, and E7405A instruments with Option AYX (fast zero span sweeptimes) perform the "Measure At Marker" and "Auto-Measure" functions using the incorrect detector.
This can only be seen if the signal being measured is at least 5 divisions down from the top graticule. When the "Measure at Marker" routine is run with all detectors selected (default configuration) the measurement may return a value for the EMI Average detector that is way too low.
Both of these problems could potentially cause the analyzer to return incorrect values for either the "Measure at Marker" or "Auto Measure" functions.
Item #1 could also cause the manual use of either the Quasi-Peak or EMI Average detector to auto-range the signal off the top of the screen.
A new firmware version has been released that corrects both of these problem. If you do not have firmware version A.14.01 or later follow the link below to the EMC firmware download site where the latest version can be downloaded free of charge.