Sam, You should also consider the radiation may be from multiple sources on the EUT. Polarization of the source may not be the same at the substitution antenna. Try 0, 45, and 90 degree polarization of the bi-con. A tuned dipole would also give you better results as a bi-con has a very high SWR. This gives you addition loose which you may not have accounted for.
Jim -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of Cortland Richmond Sent: Thursday, December 27, 2001 12:26 PM To: Sam Wismer; ieee pstc list Subject: Re: Field Strength - Substitution Method Sam, I think you did it right with one AF and one gain. There's a problem with that method. You need more information needed to make the _results_ right. Given a certain power at the antenna terminal, and a known gain and efficiency, you can calculate the free-space field strength at some distance due to RF applied to that antenna. Then you add loss or gain due to reflection from the ground plane. This gets you down to some fairly reliable way to estimate what field strength will be created over a ground plane at some distance from an antenna. 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. Cortland (my own opinion and not that of my employers) ------------------------------------------- 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: Michael Garretson: [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: 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [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: No longer online until our new server is brought online and the old messages are imported into the new server.
