Voltage or power, a dB is a dB. Constructive interference between the direct and reflected ray (given a perfectly conductive ground plane) can increase the field intensity by a factor of two if the phase difference between the two is a half-wavelength. That is 6 dB, whether you speak of the field intensity, or the signal power at the antenna port measured at the EMI receiver. Ken Javor
Phone: (256) 650-5261 From: "Sundstrom, Michael" <michael_sundst...@overheaddoor.com> Date: Thu, 22 Dec 2011 07:54:21 -0600 To: Bill Owsley <wdows...@yahoo.com>, "EMC-PSTC@LISTSERV.IEEE.ORG" <EMC-PSTC@LISTSERV.IEEE.ORG> Conversation: [PSES] Semi-Anechoic Chamber Question - Correction Factor Subject: RE: [PSES] Semi-Anechoic Chamber Question - Correction Factor Bill, I¹d guess 6dB as in voltage, with dBuV being used. Michael Sundstrom OHD / TREQ Dallas Electronic Lab Analyst, EMC Lead 2170 French Settlement Rd, Suite B Dallas, Texas 75212 (214) 579 6312 (940) 390 3644c KB5UKT Albert Einstein once said, "The definition of insanity is doing the same thing over and over again and expecting different results". From: Bill Owsley [mailto:wdows...@yahoo.com] Sent: Wednesday, December 21, 2011 11:02 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Semi-Anechoic Chamber Question - Correction Factor Go back, way back, to the paper by pate, german, smith, on the NSA. Go through all the details and calculations and surmise that there is the direct path, and the reflected path. The reflected path adds, or not, to the direct path, depending on wavelength (phase at receive antenna) and distance between antennas. A scan up to 4 meters will generally cover the apparent phase shift at the lower frequencies such that a "maximum" is recorded. This scan will certainly cover the apparent phase shift of higher freq's. The reflected wave verses the direct wave, will have a longer distance and thus a little more loss. In the worst case, it can be neglected. It will also suffer some loss at the reflecting surface, generally assumed to be a "perfect" boundary since it is unknown but defined as metal. Thus, the received voltage received via a direct path added with a reflected path, assuming no distance or reflection loss, would be 6 dB higher than the direct path alone. This direct path alone is the assumed field measured in a FAC, neglecting any chamber anomalies. Or is it 3 dB higher?? as in power? From: "Grasso, Charles" <charles.gra...@echostar.com> To: Jim Hulbert <jim.hulb...@pb.com>; "EMC-PSTC@LISTSERV.IEEE.ORG" <EMC-PSTC@LISTSERV.IEEE.ORG> Sent: Wednesday, December 21, 2011 4:29 PM Subject: RE: Semi-Anechoic Chamber Question - Correction Factor Professor Leferink published a nice paper that proposed a different correction factor for a SAC to a FAC. I tried to track it down but had no luck. Best Regards Charles Grasso Compliance Engineer Echostar Communications (w) 303-706-5467 (c) 303-204-2974 (t) 3032042...@vtext.com <mailto:3032042...@vtext.com> (e) charles.gra...@echostar.com <mailto:charles.gra...@echostar.com> (e2) chasgra...@gmail.com <mailto:chasgra...@gmail.com> From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Jim Hulbert Sent: Monday, December 19, 2011 2:27 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: Semi-Anechoic Chamber Question Thank you everyone for the helpful feedback. The consensus is clearly: Save my back and leave the absorber and ferrite tiles in place. Compare radiated emissions measurements in the chamber to those on the OATS (several suggested a comb generator for this purpose). Assign an adjustment factor to the chamber measurements to correlate as closely as possible to the OATS measurements (6dB has been suggested as a reasonable factor, although I need to confirm this through my own measurements). Jim - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
