There is a theoritical NSA program on the ETS website that will calculate the NSA for any given distance and scan height. I used it to generate numbers for a compliant 3m site (1 to 4m recieve scan height) and then ran the numbers with the transmit and recieve antenna heights at something like 30 meters. The difference was a nominal 6dB. Bob R.
--- On Thu, 12/22/11, Sundstrom, Michael <[email protected]> wrote: From: Sundstrom, Michael <[email protected]> Subject: RE: [PSES] Semi-Anechoic Chamber Question - Correction Factor To: "Bill Owsley" <[email protected]>, "[email protected]" <[email protected]> Date: Thursday, December 22, 2011, 8:54 AM Bill, I’d 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:[email protected]] Sent: Wednesday, December 21, 2011 11:02 PM To: [email protected] 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" <[email protected]> To: Jim Hulbert <[email protected]>; "[email protected]" <[email protected]> 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) [email protected] (e) [email protected] (e2) [email protected] From: [email protected] [mailto:[email protected]] On Behalf Of Jim Hulbert Sent: Monday, December 19, 2011 2:27 PM To: [email protected] 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. 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To post a message to the list, send your e-mail to <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
