The GTEM software with which I have worked was designed to correlate to 3 meters. Given that a test article that fits into a GTEM cell is physically small, the correlation to ten meters is then just a "20 log" extrapolation.
> From: [email protected] > Date: Mon, 18 Jun 2007 15:20:58 -0600 > To: "Bill Stumpf" <[email protected]> > Cc: "Kunde, Brian" <[email protected]>, [email protected], "Grace Lin" > <[email protected]> > Subject: RE: RE Measurement Distance per EU > > Has anyone correlated GTEM measurements to 10 meter data with acceptable > accuracy? > > Frank de Vall > HID Global Corporation > > > > > "Bill Stumpf" > <[email protected] > OM> To > Sent by: "Kunde, Brian" > [email protected] <[email protected]>, "Grace > Lin" <[email protected]>, > <[email protected]> > 06/18/2007 02:05 cc > PM > Subject > RE: RE Measurement Distance per EU > > > > > > > > > > We have an NSA compliant 3-meter chamber. We do not use it where 10-meter > compliance is called for. > > Bill Stumpf > D.L.S. Electronic Systems, Inc. > 166 South Carter Street > Genoa City WI, 53128 > 262-279-0120 > > > From: [email protected] [mailto:[email protected]] On Behalf Of Kunde, > Brian > Sent: Monday, June 18, 2007 2:33 PM > To: Grace Lin; [email protected] > Subject: RE: RE Measurement Distance per EU > > Grace, > > Do they make a fully compliant 3 meter semi-anechoic chamber? I wasn't > aware that a 3 meter chamber passed the NSA requirements down to 30Mhz. > > The purpose of having a Test Standard is to standardize on a method in > which testing is performed so the results can be repeated at other test > sites and hopefully have the same or similar results. When you stray from > what the standard calls out, then you take the risk of your results being > brought into question. > > I think your biggest problem with testing at 3 meter is going to be with > near field below 100Mhz. Because of the common differences seen when > testing a product at 3 meter verses 10 meter, I think there will always be > a high level of doubt in your test results. > > In my opinion, "compliance testing" can only be confidently done at a 10 > meter OATS or equivalent. > > BTW, the note in section 10.2.1 is a method to test signals that fall near > or on a high ambient. Most all OATS have at least a few areas with high > ambient and this section gives them a work around at only those > frequencies. It is not intended to allow full testing at distances than 10 > meter. In a chamber you wouldn't have any ambient signals so you couldn't > use this section to justify 3 meter testing. > > I am very curious to know the confidence level of 3 meter chambers are. > Maybe some who have such chambers will post. > > The Other Brian. > > > > From: [email protected] [mailto:[email protected]] On Behalf Of Grace Lin > Sent: Monday, June 18, 2007 1:43 PM > To: [email protected] > Subject: RE Measurement Distance per EU > > Dear Members, > > Is 3m measurement distance for radiated emission not accepted by EU? > > I propose a 3m full compliant chamber. A chamber manufacturer informs me > that EU only accepts 10m measurement distance. I checked EN 55022: 1998 > incorprating Corrigendum Nol 1 and A1 and A2. Clause 6 states: > > "The EUT shall meet the limits of Table 5 or Table 6 when measured at the > measuring distance R in accordance with the methods described in Clause > 10. ... " > > The title of Table 5 is: "Table 5 - Limits for radiated disturbance of > class A ITE at a measuring distance of 10m". The title of Table 6 is: > "Table 6 - Limits for radiated disturbanc eof class B ITE at a measuring > distance of 10m". Subclause 10.2.1 states: > > " > 10.2.1 Antenna-to-EUT distance > Measurements of the radiated field shall be made with the antenna located > at the horizontal distance from the boundary of the EUT as specified in > Clasue 6. > > NOTE If the field-strength measurement at 10m cannot be made because of > high ambient noise levels, or fo rother reasons, measurement of class B > EUT's may be made at a closer distance, for example 3m. An inverse > proportionality factor of 20 dB per decade should be used to normalize the > measured data to the specified distance for determining compliance. Care > should be taken in the measurement of large EUTs at 3m at frequencies near > 30 MHz, due to near field effects. > " > > I look forward to your comments. > > Best regards, > Grace Lin > Crestron Electronics, Inc. > www.crestron.com > > - ---------------------------------------------------------------- This > message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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