I must be missing something. The controlled impedance concept would work for me if the cable-under-test (CUT) were a single-wire-above-ground (swag) transmission line terminated at either end in its characteristic impedance. That is never the case. If a cable is shielded, then it is terminated at the equipment-under-test (EUT) in a low impedance and if it is not shielded its termination impedance reflects whatever circuit it is connected to, and whether that circuit is referenced to ground. Actually that statement about a shielded cable being terminated in a low impedance reflects my vehicle experience. Equipment designed for home or business use may well terminate a shield at an equipment chassis, but that chassis may or may not have a connection to ground, and even if it does it is a green wire of indeterminate, but not low impedance over the frequency range of the test (0.15 - 80 MHz). And ditto for an unshielded wire - the circuit to which it connects may be referenced to chassis but chassis is not well-referenced to the ground plane - in fact I do believe that CDNs built for power ports inject on phase, neutral, AND green wires simultaneously - clearly implying that the green wire is just one more fortuitous conductor.
If you are using a CDN or the injection clamp (the device that looks like an absorbing clamp but is used to inject) then the device does raise the impedance of the CUT looking toward the auxiliary equipment (AE). But that alone is hardly enough to prevent standing waves. The test technique does provide that injection should occur within a tenth wavelength at the highest test frequency, which should be sufficient to ensure that you know what level of signal gets into the EUT, provided the cable is unshielded. If the cable is shielded, what gets into the EUT is not strongly a function of the exact position of the injection device relative to the EUT, but where standing waves may be relative to shield discontinuities, such as shield terminations. In conclusion, while I don't have a problem per se with IEC-10004-6, I don't know why they went to the trouble of requiring the "vehicle-like" ground plane set up when the same set up as 1000-4-3 should have sufficed. But like I said at the beginning, maybe I'm missing something. ---------- >From: "Jim Conrad" <[email protected]> >To: "Ken Javor" <[email protected]>, "John Woodgate" <[email protected]>, <[email protected]> >Subject: RE: common mode immunity coupling units >Date: Thu, Nov 7, 2002, 6:37 AM > > Ken, > > The test set up is over a ground plane with controlled impedances to > make the test more reproducible. It is not perfect but it's better > than having the EUT 80 cm above the ground plane where the > impedances would be very high and harder to control. > > Best regards, > > Jim > > -----Original Message----- > From: [email protected] > [mailto:[email protected]]On Behalf Of Ken Javor > Sent: Wednesday, November 06, 2002 10:54 PM > To: John Woodgate; [email protected] > Subject: Re: common mode immunity coupling units > > > I have to agree with Mr. Woodgate's comment, as far as numbers go - > 150 Ohms > means the wire is very close to a well-defined ground plane if the > number > represents a transmission line characteristic impedance. However, > the IEC > 1000-4-6 test set up does not represent the real world, because it > requires > a well-defined low impedance ground plane underneath the entire test > set-up. > In my opinion, the set-up ought to look precisely like the IEC > 1000-4-3 set > up (80 cm above ground), since the purpose of 1000-4-6 is to > simulate the > results of radiated field-to-wire coupling at frequencies too low to > accurately simulate in a practical radiated set-up. > > I am curious to hear what Mr. Woodgate and others think about this > topic. > > ---------- >>From: John Woodgate <[email protected]> >>To: [email protected] >>Subject: Re: common mode immunity coupling units >>Date: Tue, Nov 5, 2002, 3:08 PM >> > >> >> I read in !emc-pstc that Ken Javor <[email protected]> > wrote >> (in <[email protected]>) about 'common mode > immunity >> coupling units' on Tue, 5 Nov 2002: >>>Because the Europeans think that is the right impedance to > simulate a >>>generic transmission line/antenna far from ground. >> >> Not 'far' from ground, AIUI, but 'not far' from ground. >> -- >> Regards, John Woodgate, OOO - Own Opinions Only. > http://www.jmwa.demon.co.uk >> Interested in professional sound reinforcement and distribution? > Then go to >> http://www.isce.org.uk >> PLEASE do NOT copy news posts to me by E-MAIL! >> >> ------------------------------------------- >> This message is from the IEEE EMC Society Product Safety >> Technical Committee emc-pstc discussion list. >> >> Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >> To cancel your subscription, send mail to: >> [email protected] >> with the single line: >> unsubscribe emc-pstc >> >> 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://ieeepstc.mindcruiser.com/ >> Click on "browse" and then "emc-pstc mailing list" >> > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > 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://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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