At the AST research location in Irvine, California, there exists what I believe may be the only commercially deployed bipolar gigahertz field chamber. This is a patented design by Dr. Andrew Podgorsky, in this case conversion of an existing, small, semi-anechoic chamber to a form of TEM cell in which uniform fields can be accurately generated over a relatively large volume. The corollary to this is, fields can be accurately measured in the at volume, and Jozef Baran, leader of the EMC group at AST, who had this built, was able to obtain FCC recognition as equivalent to an open-air test site.
If you want more information on this device, look in the annual IEEE EMC Symposium papers. Search on the inventor, Andrew Podgorski, the term "BGF", and for the installation at AST on the names Jozef Baran, and Mark Frankfurth. I had the great good fortune to work at AST while the BGF chamber was being installed, and to later see the final configuration after all testing and tweaking had been completed. While not a compete replacement for open air sites -- there IS a volume limitation -- it seems to me for for desktop and laptop computers to offer not only the promise of accurate readings without ambients, but also the possibility of automating testing (if a standard peripheral and cable configuration can be agreed on as satisfactory). Cortland Richmond ====================== Original Message Follows ==================== >> Date: 18-Jun-99 15:28:05 MsgID: 1068-84459 ToID: 72146,373 From: Gary McInturff >INTERNET:[email protected] Subj: RE: NEAR/ FAR FIELD CORRELATION ISSUES Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 The closest thing I have heard about was a claim by one of Chris Kendall's engineers that he could get correlatible data between a small ferrite shielded room and an OATS site. It did however, have to develop and antenna height factor, if you will. The room is roughly 10 by 12 by 20 feet (for Europe that's about as useful as furlongs per fortnight but anyway...) The biggest problem was the inability to raise the antenna. With some mathematically trickery they were able to apply this factor and claimed to be within a dB of the actual OATs measurement. The article didn't describe the complexity of the equipment under test so there could be a whole raft of problems there, and you would have to be of the short that believes that the FCC 3 meter testing is valid and many do not. The good news is that the cost of such a chamber starts to fall more in-line with what people can afford and even more important could be put in many buildings that already exist in every city. Now at least EMC vendors could move near us, rather than we having to travel to them, plus the other benefits that such a room can bring to the table. The bad news is that they have a long way to go in convincing the appropriate people that it really works, and they still had some problems at th 30 to 60 MHz region and were looking for some acceptance of a fudge factor in this range. Before the scoffing begins at my useless optimism, I might point out that not long ago the same problems existed for the large chambers, but many of the big kids are quite happily qualifying stuff in those. It is a long shot but I would certainly wish them success if they can do it, and any start is a good start. I haven't been in touch with them lately to know of their progress. Gary -----Original Message----- From: Roman, Dan [SMTP:[email protected]] Sent: Friday, June 18, 1999 12:29 PM To: '[email protected]' Subject: RE: NEAR/ FAR FIELD CORRELATION ISSUES I also have been following this thread with interest, but even more practical and technically less challenging alternate methods of testing take too long for acceptance in my opinion. Forget near-field measurements with probes, I'd like to see quicker movement on acceptance of standards like EN50147-3 for fully anechoic compact chambers. I'm not going to get greedy and look for (or expect) near field or cable clamp measurement acceptance in the near future. Since I mentioned it, does anyone know if there is movement or progress in the area of standards tailored specifically for compact chambers like EN50147-3? -- Dan Roman, Compliance Engineer * mailto:[email protected] *Voice: +1 (973) 993-3000 ext. 6485 Fax: +1 (973) 993-8466 --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). ====================== End of Original Message ===================== --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
