This is interesting, as Mr. Chen stated in “Practical Considerations on EMC Measurements using Field Probes” that:
“Modern 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.” 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 wasn’t 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 +/- ¼ dB variation in isotropicity (at 400 MHz & 1 GHz, but what about 6 GHz); that’s very impressive. I wonder if the probe’s 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 manufacturer’s antenna. · Then we believed that all of the manufacturer’s 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 “end-to-end” starting with a uniform applied RF field. · And now we realize that “several points per octave” 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. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
