Sorry for the delay in replying. It is clearly true that a given length of wire oriented in a particular direction could result in minimal radiation pick-up at some remote victim antenna. But in the same spirit of maximizing cable radiation during test, it is maxima for which we search.
The exact same situation arises in reverse with the relationship between requirement 61000-4-3 and 61000-4-6. If one were to measure the pick-up on an EUT-connected cable during 61000-4-3, what would be observed would be significant variation in current/potential as a function of frequency (and indeed as a function of position on the cable itself at any single frequency at which the cable is electrically long). But the 61000-4-6 limit represents the maximum of what can be picked up; there is no (futile) attempt to reproduce the precise pick-up at some point or points on the cable at each frequency. If a conducted emission cable bundle requirement were to be levied, it would be based on the same considerations. Note an important caveat, electrical length. 61000-4-6 tailors the start frequency of the test according to electrical length, recognizing that short cables are inefficient radiators. The same could and should be applied to a cable-bundle emission requirement. > From: John Woodgate <j...@jmwa.demon.co.uk> > Reply-To: John Woodgate <j...@jmwa.demon.co.uk> > Date: Tue, 8 Jul 2003 03:53:33 +0100 > To: emc-p...@majordomo.ieee.org > Subject: Re: cable maximization - do you or don't you?? > > > I read in !emc-pstc that Ken Javor <ken.ja...@emccompliance.com> wrote > (in <bb2f7186.2be2%ken.ja...@emccompliance.com>) about 'cable > maximization - do you or don't you??' on Mon, 7 Jul 2003: > >> I don't think it is at all complicated, at least in principle. Maybe a >> devil will emerge out of some details I am missing... > > It's a point worth discussing. >> >> I don't see how an end-driven wire can radiate more efficiently than a tuned >> half-wave dipole. That model can be used to convert from field intensity at >> X meters to peak current on the cable. > > Agreed that it can't be more efficient, but it can be less efficient to > a nearly unlimited extent, so making that assumption can be very > pessimistic indeed. >> >> For the case of multiple cables one could make various assumptions about the >> additive effect of emissions at X meters: >> >> A worst case assumption is that the same spectrum could appear on each cable >> and add in phase at the measurement point. This would require subtracting >> from the previously determined single cable current limit the factor: >> >> 20*log (number of cables). >> >> I think this is unreasonable, that the summing would be of random phase and >> the factor to be subtracted from the single cable current limit ought to be >> >> 10*log (number of cables). > > Agreed, as a first approximation. >> >> I am not trying to say that this approach is precisely correct and should be >> implemented as is. I do think it would be interesting to make some cable >> measurements using an absorbing clamp and compare to the corresponding OATS >> profile and draw some conclusions. > > Yes, I think that is justified, now that you have raised the subject. > Unfortunately, many such proposals are never investigated because no-one > has the time, even if the costs can be handled. > > I think we all look forward to your report of the first results. (;-) > -- > 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: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: emc-p...@hypercom.com > Dave Heald: emc_p...@symbol.com > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
