Please, Let me jump in. A Low Cost Pre-Compliance Test Area (LCPCTA) can give results almost as good as an Open Air Test Area (OATS) if you know three things 1.) The test area is free of metal and is large enough. 2.) The test area is STABLE, as in no metal moves, ground conditions do not change or are minimum, etc. 3.) How your test area compares with your commercial EMC lab. What I have done in the past is set up a test area in a warehouse (32x32 ft. with a 22 ft. high metal roof) purchased a battery powered comb generator that provided an output at 5 MHz. and every 5 MHz up to 1.5 GHz. Scanned the warehouse picking at least one frequency in each octave, like the site attenuation frequencies (80, 100, 200, etc.). Then sent the comb generator to a commercial EMC lab and have them scan the same frequencies. Now you have two sets of numbers, and from there you can determine have far off your test area is. You will need to rework the difference back into your correction factors for each lab you use. This is a simple explanation but it works and as long as there are no large changes in response at your site, you should be able to correlate. Also, use the EMC lab where you sent the comb generator for your testing. Using this method I was able to correlate with four commercial labs (OATS) and one Anechoic chamber to within 2 dB. P.S. My test area had No ground plane. I set up this pre-compliance lab for a large semiconductor company's remote design group and it is still in use today. Al Patrick, Sr. EMC Engineer - EMC lab Manager Scientific-Atlanta Inc.
-----Original Message----- From: Gary McInturff [mailto:gmcintu...@packetengines.com] Sent: Friday, July 30, 1999 11:21 AM To: 'Green, Henry'; 'Qu Pingyu'; 'emc' Subject: RE: cost effective EMC facility TEM cells large enough for a very small computer are, I believe, available. I don't have the sales literature in front of me and I haven't seen it for awhile, but in my opinion you would be better served if you invest in pre-compliance equipment, a small ground screen etc, even with a less than ideal site. Both units will take time for you to learn how to interpret the data and how it compares with the OATS you'll eventually have to us. The TEM cell will required constant manipulation of the unit to expose the various fronts to the "antenna". The pre-compliance equipment is going to have some problems because of ambient noises and lack of a proper environment, ground screen, full antenna mast height, etc. But I think you can get closer to the OATS with this equipment if you can control the electrical ambient at all, and you have considerably more flexibility at working on the EUT etc during this phase of testing. Either of these methods are only going to give you an A/B type test with just enough information to make a good educated guess as to when you are ready to go for a formal test, but having used both methods - the TEM cell much less - I'd much prefer the small parking lot type of pre-compliance system. That obviously is a personal opinion. Neither my wife or children listen to it so maybe you shouldn't either. Thanks Gary -----Original Message----- From: Green, Henry [SMTP:henry.gr...@gateway.com] Sent: Friday, July 30, 1999 6:08 AM To: 'Qu Pingyu'; 'emc' Subject: RE: cost effective EMC facility I do not believe that the GTEM is a suitable option for testing a PC due to the size limitations of the GTEM. The GTEM has, for lack of a better term, a "sweet spot" that the EUT has to occupy for optimum results. Although you might be able to place your EUT in the GTEM, it would not necessarily be confined to this "sweet spot." This being the case, the repeatability, and accuracy of your measurements would be questionable. Another consideration is the requirement that you have correlation to an OATS. Just my 2-cents worth. Henry E. Green Gateway Regulatory Compliance -----Original Message----- From: Qu Pingyu [mailto:pin...@ime.org.sg] Sent: Friday, July 30, 1999 3:38 AM To: 'emc' Subject: cost effective EMC facility Hello, everyone: I posted an question several weeks ago asking about GTEM. Thanks those who share with me your experience. I may not address my problem very clearly thus I would like to come back to you one more time. We are a R & D orgnization in Singapore mainly dealing with semiconductor industry. Since there are some requirements from our industry partners in the area of EMC design, we are considering setting up some EMC measurement capabilities. At the intial stage, we will only consider equipment for radiated emission/susceptibility testing. Our objective is to evaluate the EMC performance of the product from our customers, being of PCB level or system level. Based on those results, we can help our customers to improve their product EMC design so that their product can pass the final compliance testing. The EUT could be small, such as integrated circuits on PCB, but it can also be large such as a PC. Due to our budget constraint, I think GTEM maybe a good choice. Do you guys agree ? If not, any other suggestions ? Thanks in advance. Best Regards Qu Pingyu --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
