My understanding is: Video Averaging is a function which is available on spectrum-analysers with digital displays. It averages the amplitudes of a programmable number of successive trace sweeps. The display must be showing a linear amplitude scale for the amplitude averaging to yield a meaningful result.
On the other hand, Video BW limiting is used to approximate the time-constant of an AVG detector when only PK detection is available. The reduced BW of the video amplifier mimics the time-response of an Average Detector. It does not rely on the log or linear display setting. Depending on the type of signal and its PRF, the two approaches may yield very different amplitudes. I think this distinction may have been missed in previous message threads on the general topic. This is a good discussion regarding AVG and Peak detection in the "EMC Handbook" Vol 2, by Don White Consultants Inc. Ralph McDiarmid, ASc Compliance Engineering Group Xantrex Technology Inc. From: [email protected] [mailto:[email protected]] On Behalf Of Cortland Richmond Sent: December 16, 2004 1:04 PM To: Alex McNeil; ieee pstc list Subject: Re: Conducted Emissions PK/AVG Alex McNeil asked: >> Is the problem that the Test House may have used "AVG BW 30KHz" and >> this should have been "AVG BW 9KHz" the problem << Sure looks like it from what you posted. There've been discussions here -- it comes up every so often -- how to to do averaging on a SA. Without knowing how they did, it's hard to say for sure, but it looks like you are close enough to hit the target with a hand grenade anyway. But are you sure it doesn't say 30 *Hz*? Narrowing the bandwidth 'way down is a method used to get averaging on a SA. (I will speculate that someone might have "learned" to -- incorrectly -- use video averaging in dB mode then increase BW to compensate for the error that causes.) Cortland Richmond This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
