Hi all, Thanks for the input. For Ken's question as to why I am putting myself through this exercise is because a customer had asked me to, therefore I shall give it my best shot.
What I have learned from this is that there doesn't seem to be an industry standard method in performing substitution field strength measurements and that my deviation of up to 10dB doesn't seem to be surprising to many. John's comments below echo my thoughts exactly as to the radiation pattern of the EUT and the chosen substitution antenna. I don't understand all the discussion about the radiation pattern of the EUT versus the transmit bi-log. The transmit antenna and SG are set to reproduce the field strength of the EUT exactly(in magnitude and frequency), therefore the receive antenna really doesn't know anything has changed. I am no physicist so I could be way wrong on this. By the way, both antennas are matching bi-logs with very close antenna factors and I suppose SWR's. 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: Thursday, December 27, 2001 5:14 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 <200112271228_mc3-ec1b-a...@compuserve.com>) about 'Field Strength - Substitution Method', on Thu, 27 Dec 2001: >What you don't have -- and what, I think, is most difficult -- is a model >that reliably correlates a substitution antenna as a source with the >equipment under test. A rack seven feet tall and two feet on a side -- with >wires overhead and off to its sides -- will NOT radiate the same as a >dipole. And it will differ more from an antenna as its dimensions become >larger than the antenna. I would expect differences to become more >pronounced, in other words, at higher frequencies. This is what you saw. I don't think that's relevant. The EUT, whatever it is, produces X dB(uV/m) at the receiving antenna. The sig gen and bilog is then set up to produce the same field strength at the receiving antenna. The problem seems to be *independent of the EUT*. The calculated field strength of the sig gen and bilog doesn't agree with the *measured* value. Having said that, an EUT may have an entirely different radiation pattern from that of an antenna, but the normal OATS procedure is 'blind' to this, even if the EUT is large enough to subtend quite a large angle at the receiving antenna, so that the measured field strength is actually an average over a considerable volume of space. -- 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.
