Alex,
 
You are on the right track. However, even a VBW of 9 kHz will not yield a true
average measurement in this frequency range.
 
First of all, it is not likely that the spectrum analyzer meets CISPR
requirements as a test receiver. Second, using video averaging as a substitute
for an actual average detector requires a VBW that is significantly less than
the RBW, and the amplitude scale must be linear instead of log (the average of
the log is different than the average). This is a highlight of the most
important settings - CISPR 16 will have the detailed requirements from which
suitable and/or reasonable instrument settings can be determined.
 
It is not surprising to hear of these differences - the receiver measurement
definitely takes precedence over the spectrum analyzer.
 
Thanks,
Mike

From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of
Alex McNeil
Sent: Thursday, December 16, 2004 8:19 AM
To: emc-p...@ieee.org
Subject: Conducted Emissions PK/AVG


Hi Guys,
I had a product tested that failed the conducted emissions. The switch mode
power supply was the problem. It runs at approx. 200KHz. The failed readings
were in the 150KHz to 600KHz band. The peaks were over the Avg and below the
QPk, so the Avg test was done. This resulted in the failures. However, after
close examination of the Test lab results, the printout showed IF BW 9KHz AND
AVG BW 30KHz below the graphical and tabulated results. The tests were done on
a SA. I have a receiver here and my test results for PK are the same as the
Test Lab but for the Avg my test results are significantly lower than the Test
House.
 
Is the problem that the Test House may have used “AVG BW 30KHz” and this
should have been “AVG BW 9KHz” the problem or am I missing something here?
 
Thank you for your time, it is always appreciated.
 
Kind Regards
ALEX

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