Thanks Ken. I would expect that 300+ MHz isn't much of a problem. I know that lower frequencies are a problem, especially if you start at ~27 MHz in a small chamber. I am not sure how much the small chamber loads the antenna, and how it affects the distribution of BOTH (i.e., E and H) EM field components in the intermediate range, about 80-150 MHz.
My concern is that the difference in the entire field distribution (E and H and their relation) between a small chamber and a large chamber is probably substantial up to some frequency, which depends in the first place on the characteristics of the chamber and the absorbers. Thus, the interfering EM field may be quite different in the two chambers, even though the E-field component is identical (within the E-field uniformity requirement). Knowing only the E-field seems not to be enough in case of non-plane non-uniform propagation. Ultimately, I believe that it may result in very different susceptibility thresholds in different chambers, when measured relative to the E-field only. It seems that there isn't much, if any, data published and available. Neven > > I made some measurements once in a 3 meter anechoic chamber built for > EN61000-4-3. I was interested in the disturbance a wire causes in a field > due to picking up the field, the resultant currents flowing in such a way as > to cancel the field that caused them, etc. In order to assess the effect, I > needed to monitor the undisturbed field. While EN61000-4-3 allows a x-y-z > field sensor total output to represent the field intensity, I needed to > measure the relative vector components. I found that in this tile-lined > chamber, that the only vector of any magnitude was that parallel to the > radiating antenna. I would say that given this kind of performance, a plane > wave has been established. > > But I was working at 300 MHz. I am suggesting that this simple test could > be performed at all frequencies of interest to assess the anechoic > properties of the room. > > > From: [email protected] > > Reply-To: [email protected] > > Date: Tue, 22 Jul 2003 02:35:08 +0000 > > To: [email protected] > > Cc: [email protected] > > Subject: 3m vs. 10m chamber for radiated immunity > > > > > > Has anyone investigated the difference in performance of different chamber > > sizes when performing the radiated immunity (-3) test at low frequencies > > (e.g., > > between 80 MHz and 100-150 MHz)? The field uniformity is calibrated in > > E-field, > > but I would expect the total EM field (E and H components) to have different > > distribution as a function of different chamber sizes. Specifically, keeping > > the distance between the antenna and the DUT constant at 3 m, I still expect > > different performances due to size (chamber loading the antenna and > > reflections/near field). Consequently, it seems that the interfering signal > > can > > be quite different in a small chamber vs. large chamber, with possibly large > > variations in the H-field components, even though they are both calibrated for > > the E-field uniformity, and both tests performed at the antenna distance of > > 3m. > > > > I know of a case in which testing in a smaller (3m) chamber makes product > > consistently fail at significantly lower level than in a larger, 10 m chamber > > (6 V/m vs. nearly 10 v/m). Fixing a product to pass the 10 V/m level (required > > by the customer) in the large chamber seems to be relatively easy and > > inexpensive, while fixing it to pass the same level in a small chamber may be > > very costly and time consuming. > > > > Is there any precedence like in case of the radiated emission, where 10m > > results prevail in case of a dispute? Any papers to support or dismiss my > > expectation from above? > > > > Thanks, Neven > > > > ------------------------------------------- > > This message is from the IEEE EMC Society Product Safety > > Technical Committee emc-pstc discussion list. > > > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > > > To cancel your subscription, send mail to: > > [email protected] > > with the single line: > > unsubscribe emc-pstc > > > > For help, send mail to the list administrators: > > Ron Pickard: [email protected] > > Dave Heald: [email protected] > > > > For policy questions, send mail to: > > Richard Nute: [email protected] > > Jim Bacher: [email protected] > > > > Archive is being moved, we will announce when it is back on-line. > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
