The set up documented by your test lab was PEAK detection. Using a VBW smaller than the RBW gives some measure of averaging, but it would not correspond to a true average, because if you are using a log amplifier, you are averaging log response, which is not the same as averaging linear response (geometric vs. arithmetic mean). If the signal you are looking at is pure cw, it won't make any difference. Of course, a peak measurement will yield the same measurement for that as well. If you really need a precise average response, you would need the right averaging time constant (1/VBW) and you would have to be in linear mode, meaning before you switched >from log to linear you would need to adjust the reference level very close to the signal peak because the dynamic range in linear mode is so much smaller than that in log mode. This is time consuming. I would only do it at signals which had a broadband characteristic such that it would really matter. I would expect that most signals above 1 GHz would tend to be cw and it would be unnecessary.
> From: "Ridler, Samantha" <[email protected]> > Date: Mon, 23 Aug 2004 08:21:52 +0100 > To: "'[email protected]'" <[email protected]> > Subject: Average Detection > > Hello All > > FCC part 18 requires the use of an Average detector. For measurements above > 1GHz on a HP8593E EMC (Spectrum) analyser, would using a Video Average of > 100 or more be equivalent to taking a measurement with an Average detector? > > > It has been suggested to me by a test house that this is the case, but I > have not managed to find any rationale for this. > > The setup for the Analyser in question during the measurent was as follows > if this helps: > SPAN = 2GHz, RBW =1MHz, VBW = 3MHz, SWEEP =40ms > > Many thanks. > > Samantha Ridler BEng MIEE > Compliance Engineer > > ---------------------------------------------------------------- > 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: > > Ron Pickard: [email protected] > Dave Heald: [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: Ron Pickard: [email protected] Dave Heald: [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
