Ken:
Whenever I wrote an EMCTP, I typically included a 10 dB pad for CE102, especially if I felt (yes, a very subjective guess) that the system would be relatively quiet. And when I actually got into a test, if the system was extraordinarily quiet, I would suggest going to a 3 dB pad. Interesting that you prefer placing the pad at the LISN output port for matching reasons. I typically have done that, but only for the reason of not liking to convey any higher amplitude signals through a coax than is necessary. It's always a weird feeling to find you have been doing the right thing for the wrong reason. That's an unfortunate prediction about the keepers of 461; I had thought that they lived and worked in the real world, where such data (when and if you can get your hands on it) is regularly used to guess integration risk. I can assure those "officials" that, for instance, if I were evaluating three power supplies to integrate into my system, and all claimed 461 compliance, I would still want to review their actual test data. All others things aside, I would much rather buy the 30 dB under model than the 7 dB under model. Ed Price El Cajon, CA USA From: Ken Javor [mailto:[email protected]] Sent: Thursday, April 12, 2012 8:06 AM To: [email protected] Subject: Re: [PSES] 461 CE102 Attenuator Value Ed, I don't recall why the specific value of 20 dB was selected, but you have hit on all the reasons a pad is necessary. The first reason is the issue of protecting the EMI receiver/analyzer, and I suspect the largest pad was chosen for that job that would maintain the required sensitivity. As you say, modern EMI receivers/analyzers are a good match to 50 Ohms as longs as there is some attenuation in front of the mixer; if zero attenuation is selected there is a problem with match, but that isn't the case for CE102, but only the stricter RE102 limits. The 20 dB pad is important in converting the LISN EMI port to 50 Ohms; I have been complaining for a number of years that the 20 dB pad needs to be placed at the LISN EMI port rather than somewhere else. See Figure CE102-3 between -461E vs. -461F as a result of such complaints. All MIL-STD-461 limits/test methods are tailorable, so if there is some good reason to reduce the 20 dB pad to a lower value, that may be suggested to the customer. Finally, while I sympathize with and share your desire to use EMI test data not just for pass/fail compliance but for information, that is most assuredly not the official reason for MIL-STD-461, and any assertion otherwise will be met with withering condemnation, from any official source. Ken Javor Phone: (256) 650-5261 - ---------------------------------------------------------------- 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 <[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]>
