In the words of an old colleague, "chambers and race cars are alike in that there is no substitute for cubic inches."
That said, absorber material works best when the angle of incidence is a close to straight in as possible. Thus, for a given separation distance between transmit and receive antennas (or source/EUT and receive antenna) the wider and taller the chamber, the better (within practical limits, of course). Other answers are noted below in red. Best of luck. Have fun! Ghery S. Pettit Pettit EMC Consulting gh...@pettitemcconsulting.com (360) 790 9672 From: Pawson, James [mailto:james.paw...@echostar.com] Sent: Friday, April 29, 2016 12:14 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] Anechoic Chamber Questions Hello all, I have some questions about anechoic chambers that I need some help with and I'm sure there is some expertise in this group that can help. 1. My understanding is that an anechoic chamber is meant to simulate a reflection-less, free space environment. Therefore if you move a source towards / away from the antenna, the signal level should follow the inverse square law - correct? That is the theory, anyway. J 2. When comparing absorber types (hybrid + ferrite tile vs. foam absorber) the return loss characteristic gives the amount of absorption at a particular frequency - correct? Correct 3. If I wanted to compare effectiveness of foam absorber with hybrid + tile absorber is it just a case of adding the return loss of the hybrid to the return loss of the tile to achieve a final figure? My understanding is that the hybrid helps match the wave impedance from free space to that of the tile. Is the return loss of hybrid + tiles _together_ greater than the individual return losses of the separate components? Manufacturers that I've looked at list the data separately. The only number that really matters is the performance of the combination. I'm not sure that you can simply add them. 4. I have been told that the distance between absorber and a reflective metal backing is important for ensuring that the returning wave is in anti-phase (or at least as much as possible) with the incoming signal. However information on acceptable limits for this distance seems sporadic or in rarefied scientific papers behind paywalls. Does anyone have any info or experience on this point? While this might be true, keep in mind that the required distance would be a function of frequency. So, I wouldn't lose too much sleep over this question. Many thanks for your time, I'm trying to get a handle on our chamber's performance and any answers will help. Regards, James - ---------------------------------------------------------------- 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://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> 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://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
