Hi All, Thanks for all your input. I believe I have a better handle on it now.
Kind Regards, Sam Wismer Engineering Manager ACS, Inc. Phone: (770) 831-8048 Fax: (770) 831-8598 Web: www.acstestlab.com -----Original Message----- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of John Woodgate Sent: Friday, December 28, 2001 1:31 PM To: emc-p...@majordomo.ieee.org Subject: Re: Field Strength - Substitution Method I read in !emc-pstc that Cortland Richmond <72146....@compuserve.com> wrote (in <200112280904_mc3-ec2a-3...@compuserve.com>) about 'Field Strength - Substitution Method', on Fri, 28 Dec 2001: >This isn't the issue. The receiving antenna, as you say, can't tell. The >problem is the substitute antenna. > >We assume the source is a dipole (or, here, a bilog) at every frequency. >Our substitute antenna has a simple pattern (even a bilog - we spend a lot >of money to get it, too). The source is not so simple. Even if it IS a >half-wave dipole at (say) 100 MHz, at harmonics it is a wavelength long or >more, and radiates in sheaves of cones oriented at some angle along the >axis of the wire (a LP does NOT do this!) - most of which may miss the >receiving antenna completely on an OATS. The angles along the wire decrease >as the frequency increases. It will have gain over a dipole; the lobes off >its ends narrower and stronger than those from a dipole fed with the same >power, and at high enough harmonics, close enough to the axis of the >conductor that they are again directed towards the receiving antenna as we >turn the EUT. > >This will bias calculations which assume the source has a simple pattern at >_every_ frequency. It doesn't. I just don't buy that. The receiving antenna is measuring the field strength at its position (actually some sort of average over its volume). How that field strength is produced is irrelevant - whether it comes from the bilog or the EUT. Besides, limits are based on the direct measurement of field strength by a receiving antenna. Only the changes of height and polarization search the actual emission pattern of the EUT, with a VERY broad brush. Emissions in narrow lobes in other directions and emissions at harmonic frequencies are not measured, but that is not an error - they are either measured at another stage (higher frequency measurements or during rotation of the EUT) or are not required to be measured. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.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: No longer online until our new server is brought online and the old messages are imported into the new server. ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.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: No longer online until our new server is brought online and the old messages are imported into the new server.
