There is a fundamental difference between assigning an uncertainty factor that is in fact a hard number, like NSA, vs. something that has to be wagged, like the effect of cable placement on radiation efficiency in the direction of an antenna.
In fact, this is an excellent example of when a large, but uncontrolled uncertainty points us in the direction of another control altogether. The radiation efficiency of a cable, relative to its max efficiency, will vary >from something close to zero, up to one. Obviously some assumptions are made that place the actual efficiency somewhere in the vicinity of unity, with some uncertainty as to how close unity is approached, based on assumptions about the quality of test personnel, and the time they take to do the maximizing. This is an area where human engineering, or perhaps human factors has to be factored into the test equation. If a test sample is very quiet, some quick cable manipulations can be performed, and if no significant changes are observed, there is no point in further effort. Likewise, if a test sample is very noisy, there isn't any point in maximizing emissions. It is only when something is just passing that it is important to take time to move the cables to maximize emissions. It is precisely here, that to the test customer, it appears the test house is spending his money (time to manipulate cables and scan and re-scan) to fail him. A much better approach was promoted about thirty years ago by a European EMC engineer named Balint Szentkuti: control cable common mode emissions over the 30 - 1000 MHz band, perhaps using the absorbing clamp to give better accuracy at these frequencies than a current probe. The limit, in dBuA, would be derived to yield the radiated emission limit at three or ten meters based on a perfectly maximized cable radiation pattern. Once that test had been performed and passed, it would be on to the radiated emission test, where cable manipulation would no longer be part of the test regime, and any emissions in excess of the limit could be dealt with by looking at the test sample enclosure and or the circuitry within. Ken Javor Phone: (256) 650-5261 > From: John Woodgate <j...@jmwa.demon.co.uk> > Date: Tue, 10 Aug 2010 22:33:13 +0100 > To: <emc-p...@ieee.org> > Subject: Re: Calibration supplier for signal generator with pulse modulation > > In message <c8872923.84265%ken.ja...@emccompliance.com>, dated Tue, 10 > Aug 2010, Ken Javor <ken.ja...@emccompliance.com> writes: > >> That is all background. The unalterable fact, regardless of how MU has >> been misapplied and perverted, is that it applies to the measurement >> facility itself; something that inherently will have an uncertainty on >> the order of several dB. It does not apply to things that can be >> measured to tenths of a dB, or are not even spec?d in dB, such as the >> modulation waveform of a signal generator, or its frequency accuracy. > > CISPR 16-4-1 appears to disagree, citing things like the height of the > antenna and even 'routing of cables' as having uncertainty assessment > applied to them (clause 4.2.4). > -- > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk > John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > If at first you don't succeed, delegate. > But I support unbloated email http://www.asciiribbon.org/ > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > Graphics (in well-used formats), large files, etc. can be posted to that URL. > > Website: http://www.ieee-pses.org/ > Instructions: http://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <emcp...@socal.rr.com> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher: <j.bac...@ieee.org> > David Heald: <dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
