It is clear that any correction table built into the field probe hardware/firmware/software is time domain only, so linearity correction factors based on amplitude, not frequency domain, because there is no frequency information unless you are looking at an entirely different kind of device designed to drive a spectrum analyzer. With that sort of system (suppliers of which I am aware include Rohde & Schwarz and Narda), it is possible to correct in in the frequency domain, but again not a single standard out there is based on the use of such, as they are quite recent developments.
Ken Javor Phone: (256) 650-5261 From: Edward Price <e...@jwjelp.com> Reply-To: Edward Price <e...@jwjelp.com> Date: Tue, 6 Mar 2018 01:27:07 +0000 To: <EMC-PSTC@LISTSERV.IEEE.ORG> Conversation: [PSES] Field probe calibration Subject: Re: [PSES] Field probe calibration This is interesting, as Mr. Chen stated in ³Practical Considerations on EMC Measurements using Field Probes² that: ³Modern probes have correction table built into the probe. Microcontrollers inside the probes apply linearity correction. As a result, probe reading reflects the true field value for CW signals. A user need not to correct for this manually.² http://ieee.rackoneup.net/rrvs/10/Zhong%20Probe.pdf I believe Mr. Chen was referring to the Lindgren HI-6005 probe in this example. It wasn¹t clear to me if he meant that the probe had an internal correction table for the frequency domain, the amplitude domain or both. I would think that isotropicity would have to be proven, not claimed, through actual measurements at time of calibration. These probes are operating at frequencies where even a block of Delrin can distort an E-field. In that document, Mr. Chen presents data for the HI-6005 which shows a +/- 14 dB variation in isotropicity (at 400 MHz & 1 GHz, but what about 6 GHz); that¹s very impressive. I wonder if the probe¹s internal microprocessor applies any correction factor to smooth the isotropicity? The amplitude and frequency linearity must also be measured, because even tiny variations in construction of the probes and electronics can cause resonances or couplings. · There once was a time when we just measured whatever came out of the manufacturer¹s antenna. · Then we believed that all of the manufacturer¹s antennas had the same factory response. · Then we required calibration data for each antenna. · Then we realized that antennas can change, so periodic calibration became a must. · And then we realized that calibrations needed to be done ³end-to-end² starting with a uniform applied RF field. · And now we realize that ³several points per octave² is not good enough resolution. · And now that we have microprocessors plucking fudge factors off an inaccessible table, we have yet another layer on this data onion, and we have to know what it does to our raw data. Ed Price WB6WSN Chula Vista, CA USA From: Patrick [mailto:conwa...@gmail.com] Sent: Monday, March 05, 2018 1:36 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Field probe calibration A great presentation on field probes can be found on the web. The author is Zhong Chen, an engineer with one of the probe manufacturers. I was lucky enough last year to be in the audience for a live presentation of this at our local EMC Chapter. I found it by searching: "ets lindgren e field probe theory" It states, among other things, that frequency response correction is applied during end use! Unfortunately, it doesn't state the amount of correction needed, nor the frequency resolution needed (doh!). But, it does answer questions on whether modern probes are frequency dependent devices. It is an interesting presentation, and I highly recommend it for anyone that wants to learn more about their test equipment. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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