Pat, I use a TEM cell for some IC measurements and can answer a couple of your questions. My answers are in BLUE below. Dave Cuthbert Micron Technology
From: [email protected] mailto:[email protected]] On Behalf Of [email protected] Sent: Wednesday, November 17, 2004 12:19 PM To: [email protected] Subject: Using TEM cells for radiated emissions at 30MHz Hi: I was given some literature by management recently advertising the use of a TEM cell for radiated emissions: http://www.wavecontrol.com/index2004.php?idioma=2 Our people have the impression that a TEM cell small enough to fit on a table-top could eliminate the need to go to the local OATS. I don't think it's that simple, but I need more solid information. The products I test are component power supplies, using CISPR 22 Class A & Class B limits. Most of our emissions are in the range of 30-100MHz. 1) I've heard TEM cells need correlation to an OATS. Is this a one-time correlation (like a calibration), or is it tied to the model being tested? 2) The dimensions of the TEM cell appear small compared to a wavelength at 30MHz. Does the issue of near-field and far-field zones still apply in a TEM cell? If so, how do you correlate the two? There appears to be no issue with this. I believe the E and H fields assume the impedance ratio of the cell as the energy propagates along the cell. I would like to hear what others say about this. 3) The product appears to have pyramid absorbers inside (no reverberation). Does this mean the EUT needs to be repositioned several times during the test? Yes, unfortunately it must be repositioned in six orientations if you want to cover all possibilities. However, since a DUT is normally placed in one plane only (I.E. on the feet) at an OATS, I suppose the DUT needs only four orientations in a TEM to mimic a DUT being rotated at an OATS. Comments? 4) How do the TEM cell correlation factors and noise floor of the spectrum analyzer interact? Do I need a certain maximum noise floor in order to make measurements? The same as any other SA measurement. At least a 6 dB S/N ratio is needed and preferably >10 dB. I'm looking for a TEM cell tutorial, or maybe a book or paper titled 'TEM Cells For Dummies'. I wrote to the vendor, but they haven't responded. On a slightly different note, has there been any progress for accepting emissions measurements from reverberation chambers (IEC 61000-4-21)? Thanks in advance, Pat Lawler EMC Engineer Condor DC Power Supplies, Inc. -------- ------------------------------------------------------- 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 [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
