Original post answer from here - COST.
________________________________ From: Ken Javor <[email protected]> To: [email protected] Sent: Tuesday, December 6, 2011 5:11 PM Subject: Re: [PSES] Calibration practice for EMI test transducers Re: [PSES] Calibration practice for EMI test transducers This discussion has gone far a field from the original post. I’m assuming some sort of scan has been run and a continuous sweep is available. The question is, how densely does that sweep need to be digitized? Not as a practical matter, but as a matter of compliance with standards or standard practice. What manner of antenna would have performance as cited below where at 100 MHz the antenna factor is 10 dB and at 120 MHz it is 12 dB, but at 110 MHz it could be 20 dB? Let’s generalize the question to any closely spaced frequencies. Let’s look at the types of antennas available. 30-200 MHz: A half-wave tuned dipole is nowhere near that sharp. Neither is a biconical. 200 – 1000 MHz: A half-wave tuned dipole is nowhere near that sharp. Neither is a logperiodic, log-spiral, nor a Yagi. 1 GHz+: Logperiodic, log-spiral nor pyramidal horns act the way surmised. My conclusion, and the point here is to invite discussion, not close it out, is that no test-type antenna is a high “Q” device. Antennas can have arbitrarily high gains, depending on construction, but the high gain is a geometrical quality, not a high quality factor in the frequency domain. Ken Javor Phone: (256) 650-5261 ________________________________ From: <[email protected]> Date: Tue, 6 Dec 2011 11:25:43 -0800 To: "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> Cc: <[email protected]> Subject: Re: [PSES] Calibration practice for EMI test transducers Yet how far would you take that argument? If it's say 11.1db at 110MHz and 11.5dB at 112MHz, would you still worry about factor at 111MHz? At some point surly this all becomes rather silly. _____________________________________________________________________________________ Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Regulatory Compliance Engineering From:"ce-test, qualified testing bv - Gert Gremmen" <[email protected]> To:[email protected] Date:12/05/2011 10:06 PM Subject:Re: [PSES] Calibration practice for EMI test transducers ________________________________ If at 100 MHz your sensor indicates during calibration 10 dB and at 120 MHz 12 dB, how are you going to know the value at 110 MHz. It maight be 20 as well as 0 dB, you don't not know as you did not measure/ calibrate. This requires some knowledge about the behavior of the sensor, and the 1/BW is and indication of that. There is another aspect in EMI measurements. As the measuring receiver interpolates between the calibrated samples, the max interpolation error (lin interpolation) is 50% of the vertical differences between calibration points. If the measuring receiver is +/- 0.5 dB you should register a calibration each time the difference between previous and current sample is 0.5 dB. Then the total error will be slightly more than 0.5 dB. There are more sophisticated interpolation methods such as cubic spline and polynomial interpolation, and the error item is subject to higher mathematics..... Play with it at: http://terpconnect.umd.edu/~petersd/interp.html<http://terpconnect.umd.edu/~petersd/interp.html> or at http://www.ibiblio.org/e-notes/Splines/Lagrange.htm<http://www.ibiblio.org/e-notes/Splines/Lagrange.htm> you can actually move the points on the latter page. Gert Gremmen -----Oorspronkelijk bericht----- Van: [email protected] [mailto:[email protected]<mailto:[email protected]> ] Namens Cortland Richmond Verzonden: dinsdag 6 december 2011 3:01 Aan: [email protected] Onderwerp: RE: Calibration practice for EMI test transducers I recently had occasion to verify on an 8591EM generic factors for an EMCO current clamp during pretest, and used its tracking generator to see if with a short wire the result was a straight line on the screen. That simply called for paying attention to 1/BW. Cortland KA5S On 12/5/2011 5:33 PM, Ken Javor wrote: If an antenna, current probe or other transducer is going to be calibrated over its frequency range of operation, what determines the step sizes between measured frequencies, or if swept, what determines the density of test points reported? - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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