I think you have described the potential problems very well Bob. I have experienced the issue where the initial point was a worst case a particular frequency in the initial calibration frequency sweep. Pain in the backside for time lost in the process.
That said, I think an initial evaluation to the constant field method is a great diagnostic tool, especially if it is done at 80% over the required CW levels. It should quickly show off shortcomings/non-linearity/compression in the system that need to be addressed. As you note, it's also good to be able to use a spectrum analyzer to monitor the status of harmonics on a directional coupler from the power amp while the field probe data is coming back. Respectfully, Brent DeWitt Milford, MA From: Bob Richards [mailto:[email protected]] Sent: Wednesday, February 01, 2012 2:52 PM To: [email protected] Subject: Re: [PSES] IEC 61000-4-3 Field Uniformity Measurement Wendy, It is my belief that the best way to go is the constant power method. This is especially true if the chamber may be marginal with respect to uniformity, and also if the amplifier is operating close to its limit. Example: If you have a field uniformity situation where one of the corners is very low, you may not have enough margin with the amplifier to be able to drive that probe position to the required level. There is a good chance that this probe position will be lumped into the 25% that are discarded anyway. Driving the amp close to its limit will also drive up the harmonics in the field enough that the field probe may start responding to the harmonics instead of the fundamental, which is especially true with some of the bilog antennas at the lowest frequencies (I've personally witnessed this). This will cause errors in the uniformity calculations. Using the constant power method, you record the power required to level at one probe position (I pick one in the middle) then replay that level at all the probe positions and use the probe readings to calculate uniformity. Just make sure that the lowest probe readings are well above the probe's noise floor. Now if you have a REALLY good chamber, a really flat response antenna with a wide beamwidth, and an amplifier that is 4 times more than what is needed, either method will work well. :-) Bob R. --- On Wed, 2/1/12, WNya <[email protected]> wrote: From: WNya <[email protected]> Subject: IEC 61000-4-3 Field Uniformity Measurement To: "EMC-PSTC" <[email protected]> Date: Wednesday, February 1, 2012, 4:35 AM 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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