I assume the time-constant of the AVG Detector is specific in CISPR 16 and that this standard is called out in FCC Part 15.
I think if the VBW was placed before the LOG amplifier in the signal chain, it would yield the correct response. If placed after the LOG amp, the BW limit would not provide the desired effect. The UL EMC software we use has tick-boxes for AVG detection, but they have no noticeable affect on the receiver actions nor on the screen plot. Updated versions of this program from UL have also failed to provide a AVG detection function. It could be that this is not available on our 8568B. So, in the rather rare instance where we need to do an AVG conducted scan, we simply reduce the VBW in the test setup file to 10Hz. Ralph McDiarmid, ASc Compliance Engineering Group Xantrex Technology Inc. From: Brent DeWitt [mailto:bdew...@ix.netcom.com] Sent: December 18, 2004 8:02 PM To: Ken Javor; Ralph McDiarmid; ieee pstc list Subject: RE: Conducted Emissions PK/AVG Your point is well taken Ken, and this certainly is interesting. My approach to the concept of "average" does indeed run afoul of the limitations of measurement devices and the potential for instrument dependent results. To the best of my knowledge, the FCC is the most ill-defined with respect to the averaging time constant. That is what initially lead me to my stated empirical method. Other thoughts are welcomed! Brent > -----Original Message----- > From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On > Behalf Of Ken Javor > Sent: Friday, December 17, 2004 8:14 PM > To: bdew...@ix.netcom.com; Ralph McDiarmid; ieee pstc list > Subject: Re: Conducted Emissions PK/AVG > > > 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. 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 > > > > ---------------------------------------------------------------- > 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. 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