Now this is getting interesting. If you arbitrarily reduce the VBW until you see no time dependent amplitude variation, I think that leads to non-repeatability. That is, if my spectrum analyzer has a 1 Hz VBW, and yours has a 10 Hz VBW, we could get different answers. At least at one time, there was a specified time interval over which the averaging was to occur, which is another way of saying the the video bandwidth was specified.
I think the idea of average detection is to be able to get an accurate assessment of the value of a cw or near cw (AM) signal, possibly in the presence of broadband noise. Considering that "pulsed cw" was considered by the military to be a narrow-band signal, it would seem that the specific averaging time period would be very important. On the other hand, MIL-STD-461 has for almost forty years required peak detection of all signals, whether NB or BB. Go figure. I'm rambling on, but the point I am trying to make is that I believe average detection should have an associated time constant, somehow relating to the information content of the communication link protected by the radiated emission limit in question. > From: "Brent DeWitt" <bdew...@ix.netcom.com> > Reply-To: <bdew...@ix.netcom.com> > Date: Fri, 17 Dec 2004 18:39:11 -0800 > To: "Ralph McDiarmid" <ralph.mcdiar...@xantrex.com>, "ieee pstc list" > <emc-p...@ieee.org> > Subject: RE: Conducted Emissions PK/AVG > > Hi Ralph, > > The HP 8568 and 8566 have a "video averaging" function, which averages > multiple digital traces (up to 100 if I remember correctly). It can be used > in conjunction with a narrow VBW to get very close to a true "average" > measurement. I've always been rather empirical about the averaging > criterion. On a spectrum analyzer in zero span and linear detection, I > simply reduce the VBW and possibly add video averaging until I don't see any > more variation in the screen trace and call it done. > > Brent G DeWitt > Laboratory Manager > CKC Laboratories > Redmond, WA > email: brent.dew...@ckc.com > phone: 425-883-4757 > cell: 425-417-8228 > > >> -----Original Message----- >> From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf >> Of Ralph McDiarmid >> Sent: Friday, December 17, 2004 11:51 AM >> To: ieee pstc list >> Subject: RE: Conducted Emissions PK/AVG >> >> >> I suggest there is an important distinction between "video averaging" >> and "average detection using limited VBW". >> >> If this is correct, can someone enlighten those of us who are unsure? >> >> Ralph McDiarmid, ASc >> Compliance Engineering Group >> Xantrex Technology Inc. >> >> >> -----Original Message----- >> From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org] 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. 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Website: http://www.ieee-pses.org/ >> >> To post a message to the list, send your e-mail to emc-p...@ieee.org >> >> 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 emcp...@ptcnh.net >> >> For policy questions, send mail to: >> >> Richard Nute: ri...@ieee.org >> Jim Bacher: j.bac...@ieee.org >> >> 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 emc-p...@ieee.org > > 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 emcp...@ptcnh.net > > For policy questions, send mail to: > > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > 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 emc-p...@ieee.org 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 emcp...@ptcnh.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
