Hi David,
An interesting set of results! I'm going to ask some questions that I'm sure you've already considered so please bear with me being Captain B. Obvious. Do your field probes use frequency correction? I'm not familiar with a wide range of probes but my Narda PMM field probe has an internal calibration table; you tell it what the field frequency you are applying is and it makes the appropriate correction. However, looking at the typical correction data from the manual (see PDF page 12 of this doc: https://www.emctest.it/public/pages/strumentazione/elenco/Narda/EP%20600/Man uali/EP600-EP601EN-90302-2.02.pdf) it doesn't look like a large difference. Is there a difference in the probe construction between the probes used? Some probes like the Narda one above have two antenna per axis whereas ones like this Amplifier Research probe - https://www.arworld.us/html/18200.asp?id=636 only have one antenna per axis. Perhaps the proximity of copper plate makes a difference. On the subject of copper plate, what are the differences without this present? What are the dimensions of it and are they significant at the frequencies selected? Have you acquired just spot readings or a full frequency sweep? There may be some patterns in the frequency sweep data that give you more of a clue as to what's happening. An interesting puzzle and I look forward to hearing about your results further! All the best James From: Schaefer, David [mailto:[email protected]] Sent: 04 March 2018 05:22 To: [email protected] Subject: [PSES] Field probe calibration I took data with 4 field probes, 3 different models. All calibrated. Two calibrations by the manufacturer, two by a reputable cal house. 200-1000 MHz data, 10 MHz step size, 60 V/m level. I recorded the forward power, and all equipment and software in the setup was the same, barring only the measuring field probe and associated probe factors. Composite values only. No 3-axis data as I don't have 3-axis calibration data for all probes. Probes were 10 cm above a copper bench, DRG antenna 90 from the bench. The results are not encouraging. The tables below show the results in watts of forward power for select frequencies. Antenna Horizontal - values in Watts Probe 1 Probe 2 Probe 3 Probe 4 Max-Min(Watts) 200 MHz 85.17 144.4 135.9 97.75 59.23 220 MHz 92.81 171.6 157.4 113.5 78.79 500 MHz 21.7 34.93 28.58 26.94 13.23 900 MHz 25.57 37.25 25.6 32.42 11.68 Antenna Vertical - values in Watts Probe 1 Probe 2 Probe 3 Probe 4 Max-Min(Watts) 200 MHz 18.94 25.12 22.55 18.82 6.3 330 MHz 34.1 40.69 46.29 39.41 12.19 780 MHz 35.52 53.03 29.87 32.83 23.16 930 MHz 56.63 47.01 64.26 107.7 60.69 There are trends in the data. Probe 1 was usually the lowest. Probe 2 was usually the highest, rarely the lowest. If you want to talk field strength effects this will mean, depending on the probe, you could have an E-field 40% higher between two 'identical' calibrations. The large variance between which probe was highest or lowest based on freq. is troubling, as is the clear difference between horizontal and vertical. I took additional data with two probes of the same model rotated around a center axis. I don't have that all compiled, but just comparing one probe against itself, laying on the left, right, and bottom sides, results in up 20% difference in required power. I have not read IEEE 519, but plan to soon. So my question to this group - do you think field probe calibrations are accurate? How can we have confidence in our results with such widely varying results? Thanks, David Schaefer - ---------------------------------------------------------------- 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 <[email protected] <mailto:[email protected]> > 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) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <mailto:[email protected]> > David Heald <[email protected] <mailto:[email protected]> > - ---------------------------------------------------------------- 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 <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
