Hello – Like Neven, we are in the process of building a compact semi-anechoic chamber and have just finished the NSAs on it. I concur with everything that Neven wrote in his email and would like to amplify on one or two points. First, it is essential to do the volumetric NSAs even in a CAC. Yes its difficult but with some care this will tell you the size of the quiet zone in the chamber. Second, you will need an EdMax calculator to get the ideal NSA above 1GHz.
Best Regards Charles Grasso ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, May 03, 2010 10:00 AM To: [email protected] Subject: Re: compact semi-anechoic chamber Jan, I have had it before and I am in a middle of getting one now. The difference is that years ago I used a fully-anechoic CAC and this time I am getting a semi-anechoic CAC. 3m test-distance in any case. Depending on what your needs are, a CAC can be very cost-effective and reliable tool. It can reduce your dependence on and cost you pay to the external test house by a large amount. You'll still need to use an external lab for the radiated emission tests (I recommend you go to 10m chamber only in that case). You should be able to run the radiated immunity test without going to an external lab. Of course, if you need formal certificates, you'll need an accredited lab for the final tests and reports. The main drawback of a CAC compared to a standard-size chamber is that in the lower frequency range, from 30MHz up to 200-300 MHz (depending on the chamber) the NSA will deviate more than you'd like. It is typically +/- 6dB, and in fact it does typically deviate full-swing from -6dB to +6dB, then it settles to the mid-range of the tolerance once it reaches 200-300 MHz. For a contrast, the NSA of the 10m or 3M of fully-complian chambers is required to be within +/- 4dB, but in reality it can be much tighter than that in a good (and large) chamber. Keep in mind, however, that the NSA is typically measured with dipoles. If your DUT is large, it will couple differently (and stronger) with the chamber, increasing the uncertainty of the measurement. On the other hand, if it is much smaller, the effect of the coupling between the DUT and the chamber is lower and you will have a chance of getting much more precise results (when compared to a "perfect" chamber). The size of your DUT includes the cables that are attached to it. See if you can discuss what ferrite absorbers your vendor would install. It can make a large difference. I have not done it, but I wish I had. I am not sure if they would be willing to even consider that option to discuss, since they are pretty much tied to the ferrite-vendors. But I know that there are different tiles around, not all the same in the lower-frequency range. Long ago, ~18 years go I participated in comparative measurements, Toyo grid absorbers were by far the best you could get. I think they were also much more expensive and that it may have been the reason why they are not seen in the chamber. I am not sure what the situation is now. My currently-built chamber is almost completed, and so far I have had a very good experience with Panashield. Best, Neven From: "Mobers Jan (ST-VS/ENG1)" <[email protected]> To: [email protected] Sent: Monday, May 3, 2010 2:28:30 AM GMT -08:00 US/Canada Pacific Subject: compact semi-anechoic chamber Dear EMC-PSTC-ers, Has anyone some positive or negative experience with a Compact semi-anechoic chambers ? At the moment we searching for a enlargement of our EMC workbench set-up. We want to use such a COMPACT semi anechoic room for as well radiated-immunity and emission tests on small products (20x10x 10cm) and units with a dimension of 50x45x20 cm. There are a lot of manufacturers in this world, but we looking forward for a 2 or 3 m antenna distance. Maximum fields strength 20V/m in a freq range 30 MHz till 3 GHz. I would appreciate to receive some feedback of users of such Compact semi anechoic chamber, or even some advice and attention points to look for. Many thanks in advance. Jan Mobers - 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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]> - 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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]> - 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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]>
