Patrick: The probe manufacturer says something like “keep the probe box away or out of the field” or “best results are obtained with the probe placed on a slant.” But then they show us isotropicity data that promises +/- ¼ dB. It seems like those are contradictory statements. Back around 2002, I decided to dissect a dead Narda 8762(?) probe which a customer helped me drop. The Narda was a white Fiberglas, 300 MHz to 1 GHz probe that looked like a very elegant German “potato masher” hand grenade equipped with a cable that plugged into an IFI EFS field sensor. I wish I had taken some good pictures of the project, as few people venture that deep into such expensive territory. The head contained the orthogonal three-dipole array, with the conductive arms looking like gold foil on a thin Fiberglass substrate. The length of each dipole was about 1.5 inches. The sensing elements might have been thermocouples, thermistors or diodes, and they were mounted in the dipoles. Each sensor was also connected to a pair of very high resistance plastic wires (possibly doped with carbon like automotive spark plug wires) that ran to the far end of the stalk where an analog signal conditioning amplifier summed the three channels and provided a DC output proportional to field strength. I was struck by the delicacy of the sensor head, looking at what must have been a very labor intensive assembly. BTW, the signal conditioning amplifier was enclosed in a ¾” diameter by 4” long section of tubular steel, so it was obvious that this conductive mass (not to mention the shielded, multi-conductor power & signal cable) would distort the measured field and degrade the isotropicity.
Ed Price WB6WSN Chula Vista, CA USA From: Patrick [mailto:conwa...@gmail.com] Sent: Tuesday, March 06, 2018 7:37 AM To: Edward Price Subject: Re: [PSES] Field probe calibration Hello Ed - Good morning! You are correct - the factors stored in the probe correct for the non-linearities of the diode detector. ( as a side note- hearing a presentation live, and asking/answering questions, is always more educational than a sterile slide deck. i wish we all could sit through this presentation, ask questions, and have dialog. ) Did you notice the warnings about errors possible in the calibration process? For instance, the "probe on a stick" is calibrated at an angle??? And for that probe they say the electronics box should be kept out of the field??? I understand the reasons, but keeping the box out of the field is nearly impossible for most of our semi-anechoic chamber applications!! And I rarely see them used at the same angle as calibrated. How does one quantify those effects? (...a topic for another thread ?) But, getting back to the frequency response question... Here is what I recall- ... As shown in the slides, the detector is connected across a small (tiny?) dipole. the size of the dipole has some real-world limits. large enough to capture enough power to make a measurement possible. small enough to minimize disturbance in the field. the three orthogonal dipoles have to be close enough to represent the same physical space. So the size, placement and response is a compromise away from "ideal" (i.e. not flat ). ... IMHO, there is nothing revolutionary in that information. But, maybe I missed something? Let me know your thoughts. I would encourage local chapters to contact ETS, and ask them if they could present at the local chapter meeting. (DISCLAIMER - I have no affiliation with ETS, I just like the idea of learning something new about something that was thought to be settled...) - ---------------------------------------------------------------- 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>
