Brent, I'm a little confused by your statement. I think you are confusing the constant-field <-> constant-power methods (it confuses me sometimes, too).
The constant-field method requires leveling, at each probe position, to the required level (18v/m for a 10v/m test level). It does not matter where you start, you have to do them all. The constant-power method (which I prefer) requires a starting point, where the field at that point is leveled to 18v/m, then the same power levels are replayed at the other probe positions and the field levels recorded. Yes, for the constant-power method, I have run into the situation where the position I started with was in a null at one or more frequencies, but that problem is discovered quickly at the very beginning of the calibration and a different starting location can be selected. However, if you start with the constant-field method, you will end up with the same problem anyway, but it might not be until after you have already collected the data for 15 probe positions -- that ends up being the biggest waste of time. And even if you make it through, the chance that the varying harmonics levels affects the probe readings is greater. IMHO, it would be a better method to operate the amp at some constant level (lets say, approximately 50% of its rated power or the rated power of the antenna) at each frequency and record the probe readings at each location. No problems with a position being in a null at any frequency. Determine how much the power has to be adjusted to equal the required test level. At any frequency where the power had to be increased to reach this level, run the required linearity check and make the necessary harmonics calculations. It would never take longer to run the calibration, but would possibly take less time. JMHO. Cheers, Bob R. --- On Wed, 2/1/12, Brent G DeWitt <[email protected]> wrote: From: Brent G DeWitt <[email protected]> Subject: RE: [PSES] IEC 61000-4-3 Field Uniformity Measurement To: "'Bob Richards'" <[email protected]>, [email protected] Date: Wednesday, February 1, 2012, 10:39 PM I’ve been in the same situation Bob. My solution was simply to chose a different starting point in the array. I don’t believe the standard requires any specific point in the array to be used as the starting point. Brent DeWitt Milford, MA From: Bob Richards [mailto:[email protected]] Sent: Wednesday, February 01, 2012 6:46 PM To: [email protected] Subject: Re: [PSES] IEC 61000-4-3 Field Uniformity Measurement Brian, According to the standard, there is a linearity check that must be performed to insure the amp is not in saturation. This check must be performed regardless of which method is used. Granted, you will know at the end of the constant-field method that you might have a power problem, without having to run the linearity check, but it still needs to be done so you don't really save time. I've tried the constant field method before where one of the outlying points was in a null and the amp did not have enough power to pull it up to 18v/m. The only way I could complete the calibration was to use the constand power method, so at least in this scenario I had wasted time with the constant-field method. I wish I had a better chamber and bigger amp, but management just would not buy them for me. :-) Bob R. --- On Wed, 2/1/12, Kunde, Brian <[email protected]> wrote: From: Kunde, Brian <[email protected]> Subject: RE: IEC 61000-4-3 Field Uniformity Measurement To: "EMC-PSTC" <[email protected]> Date: Wednesday, February 1, 2012, 10:38 AM Do you only want to determine Field Uniformity or do you also want to determine the power you need for testing? If you use the constant power method, it works good to determine uniformity but I feel the data collected is not the best for determining test power. Using the Constant Field Strength method and storing all the data, you can determine field uniformity and better determine your test power in one test which can save time. The only thing is you have to know you have a good setup and enough power to perform the test with your amps operating well within their linear range (no clipping). The Other Brian -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of WNya Sent: Wednesday, February 01, 2012 4:36 AM To: EMC-PSTC Subject: IEC 61000-4-3 Field Uniformity Measurement Dear Experts, Two methods are mentioned in the standard - constant power calibration and constant field strength calibration. Is there a preferred method (benefits?) of one over the other? If yes, why? What would be the considerations to use constant field strength instead of constant power? Is it related to the equipment setup? Our system integrator recommended constant power method because he is, as he claimed, more familiar with it. Although both achieved the same purpose, what are the engineering differences between them? Sent from Wendy.Nya iPhone - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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Thank you. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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