Awhile ago, a criminal case was appealed on the basis that the fingerprint method used to convict the defendant had an unquantified aspect to it in that no one could say how accurate fingerprinting analysis really was. This was not a case of a partial print requiring human judgment, but rather a philosophical point: How do you KNOW that no two fingerprints (or substitute snowflakes) are alike? If you can’t quantify it, no matter how much circumstantial evidence there is to support it, then you don’t have a usable technique. That was the basis of the appeal. I don’t know how it turned out, but the fact that the appeal was allowed after over one hundred years of using fingerprints to track down and convict criminals, tells you that there has been a philosophical shift in how people think about these things, and this calibration vs. basic theory issue seems to me to be part and parcel of the same thought process. Ken Javor
Phone: (256) 650-5261 _____ From: Derek Walton <lfresea...@aol.com> List-Post: emc-pstc@listserv.ieee.org Date: Thu, 14 Feb 2008 14:13:54 -0600 To: Dennis Camell <cam...@boulder.nist.gov>, <emc-p...@ieee.org> Subject: Re: Standard Gain Horn Antenna Calibration Hi all, calibration has been an issue with me for a long time: specifically where and when it makes sense. The std gain horn is a prime example. I wonder if there is any calibration process that can be used, that is actually more accurate than maintaining mechanical dimensions of a horn modelled in some form of NEC program. Damage aside of course. So, in the case of something simple like a Std gain horn WHICH IS more accurate, the NEC model using tight mechanical dimensions, or some test method with very large measurement errors? We seem to be driven more by metrologists that do not fully inderstand practical limits.... Curious in Rockford, IL USA. Derek Walton ----- Original Message ----- From: Dennis Camell <mailto:cam...@boulder.nist.gov> <mailto:cam...@boulder.nist.gov> To: emc-p...@ieee.org Sent: Thursday, February 14, 2008 9:36 AM Subject: RE: Standard Gain Horn Antenna Calibration Dear members and Grace, C63.5-2006 states that all antennas, including horns, need to be calibrated. The earlier version (2004) had a sentence saying it was unnecessary to calibrate standard gain horns, but that was removed. The calibration of horns is a current topic of discussion at the C63.5 working group meetings and changes should be made in the next revision. The working group is always looking for new participants, so if you are interested contact C63® or me. I like Ed Price’s comments below. To me it’s like the difference between standard practice, verification and calibration. One possible verification check is the use of S11 measurements of the horn in question. This could extend the calibration cycle but may not eliminate it. Oh, and connector savers do make it easier to fix connector problems by reducing the wear on the adaptor connector. On the use of different horns; SGH have single lobed patterns, I do not know if the DRG have the same pattern across all frequencies. Regards, Dennis Camell National Institute of Standards and Technology 325 Broadway, MS 818.02 Boulder, CO 80305 USA Tel: (303) 497-3214 Fax: (303) 497-6665 _____ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Ken Javor Sent: Wednesday, February 13, 2008 10:41 AM To: Price, Edward; Untitled Subject: Re: Standard Gain Horn Antenna Calibration Ed makes an excellent point regarding the coax-to-waveguide adapter. A simple way to protect against damage is the use of an external adapter used as a “connector-saver.” Ken Javor Phone: (256) 650-5261 _____ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] <mailto:emc-p...@ieee.org%5d> <mailto:emc-p...@ieee.org%5d> On Behalf Of Grace Lin Sent: Wednesday, February 13, 2008 6:38 AM To: emc-p...@ieee.org Subject: Standard Gain Horn Antenna Calibration Dear Members, Does a standard gain horn antenna (htt ://www.ets-lindgren.com/manuals/3160.pdf) need to be calibrated when used for radiated emission measurement? A sales representative keeps telling me that calibration is not required for this type of antennas. This is against my understanding that all antennas for radiated emission measurement must be calibrated. A standard gain or pyramidal horn, with a waveguide feed, is a mechanically simple device. After an initial calibration, it should maintain its values without drift unless mechanically deformed. How much the gain will change with mechanical distortion is unpredictable, so I doubt that "period pictures" could reasonably document the antenna's condition. A double-ridged horn adds more mechanical complexity, making real periodic calibration verifications even more important. And then there is the waveguide-to-coax transition found on many lower frequency horns. You can electrically damage the little post inside the waveguide by arcing or excess heat or mechanical shock. Also, this post is often mounted to the rear of the coax adapter, and damage to the connector (from a bad cable connector) can translate into physical damage to the post location. Everything in this area is very mechanically sensitive, and also invisible to the user. I keep all of my horn antennas, both coax and waveguide feed models, on periodic calibration. Ed Price ed.pr...@cubic.com <mailto:ed.pr...@cubic.com> <mailto:ed.pr...@cubic.com> WB6WSN NARTE Certified EMC Engineer & Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (FAX) Military & Avionics EMC Is Our Specialty Grace Lin <graceli...@gmail.com> wrote: Dear Members, Does a standard gain horn antenna (http //www.ets-lindgren.com/manuals/3160.pdf) need to be calibrated when used for radiated emission measurement? A sales representative keeps telling me that calibration is not required for this type of antennas. This is against my understanding that all antennas for radiated emission measurement must be calibrated. Also, when measuring radiated emission, what is the difference between using a double ridge waveguide horn antenna ( ttp://www.ets-lindgren.com/pdf/3117.pdf, http://www.ets-lindgren.com/manuals/3116.pdf) and a standard gain horn antenna (http://www.ets-lindgren.com/manuals/3160.pdf)? I can find a double ridge waveguide horn antenna to cover frequency range of 18-40GHz. For standard gain antennas, I need at least two to cover the same range (more calibration cost if calibration is required). Thank you and look forward to hearing from you. Best regards, Grace Lin - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. - Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.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...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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