I¹m working for a customer. The customer bought the GTEM cell used. I¹m sure the manufacturer would be willing to sell the software at a price, but right now my goal is to figure out if he needs a low noise preamplifier to augment his spectrum analyzer, and if so, what noise figure and gain. For that I need a transfer function between field intensity and rf potential at the GTEM cell EMI port.
Complicating this is the customer is working to CISPR 25, i.e., automotive, which measures emissions at one meter, whereas the typical GTEM cell software for predicting emissions assumes a far field at three or more meters distance... Ken Javor Phone: (256) 650-5261 From: John Woodgate <[email protected]> Reply-To: John Woodgate <[email protected]> Date: Tue, 13 Aug 2019 15:46:19 +0100 To: <[email protected]> Subject: Re: [PSES] GTEM cell used for RE measurement Won't the manufacturer tell you? Best wishes John Woodgate OOO-Own Opinions Only J M Woodgate and Associates www.woodjohn.uk <http://www.woodjohn.uk> Rayleigh, Essex UK On 2019-08-13 15:27, Ken Javor wrote: > Re: [PSES] GTEM cell used for RE measurement I understand how the GTEM cell > works for immunity. That is quite simple, as you say. It¹s not as simple for > emissions. I think an analogy is the equation for transmitting from an antenna > is not reciprocal with receiving. One is simply a function of gain, the other > involves frequency/wavelength. I too worked with GTEM cells in the past and > understood better, and I too did a search and found the very complex formulae > (!) but now I need to be able to get from a field intensity limit to the > coupled potential at the cell coax connector, and I¹m not finding that, nor a > way to get there. > > Ken Javor > Phone: (256) 650-5261 > > > > > From: "James Pawson (U3C)" <[email protected]> > <mailto:[email protected]> > Reply-To: "James Pawson (U3C)" <[email protected]> > <mailto:[email protected]> > Date: Tue, 13 Aug 2019 07:47:56 +0100 > To: <[email protected]> <mailto:[email protected]> > Subject: Re: [PSES] GTEM cell used for RE measurement > > Hello Ken, > > Thinking aloud here: would such a factor exist as a generic formula? If I > think about this the other way round, putting 1V of RF into the coax connector > will generate 1V between the septum and ground (or between the septums? > septii? in the case of a differential GTEM like a Laplacell). > > This 1V will be spread over the distance between septum and ground, dictating > the overall field strength. This means cells with different dimensions will > have different factors. This is leaving aside the frequency response / VSWR of > the cell. > > I do recall seeing some formulae for correlation between GTEM and OATS/SAC > but that was a while ago. A quick google on the subject shows a few papers > with lots of big equations. > > I no longer have my old copy of EN 61000-4-20 but there might be some > interesting reference material in there. This standard also notes that many of > its provisions only apply to ³small EUTs² which is anything below a certain > size in relation to the GTEM volume or anything with cables attached (which > are ³under consideration²) > > > More practically, you could generate your own factors using an RF generator > and an isotropic field probe and using reciprocity to flip this around to get > a Volts out field inside factor. > > > Additional: There¹s also this NPL / York EMC guide on ³The Use of GTEM Cells > for EMC Measurements² which has some interesting info in. Its been a long > while since I¹ve read it in any depth though. > https://www.npl.co.uk/special-pages/guides/gpg65_gtem > > > Hope some of this is useful. > All the best > James > > > > James Pawson > EMC Problem Solver > > Unit 3 Compliance > Design for EMC / Pre Compliance / Problem Solving / EMC Testing / Consultancy > / Environmental & Vibration > www.unit3compliance.co.uk <http://www.unit3compliance.co.uk> > <http://www.unit3compliance.co.uk/> -- 07811 139957 > Opening Hours: Tuesday to Friday, 0830 to 1800. Closed Monday. > > > From: Ken Javor <[email protected]> > <mailto:[email protected]> > Sent: 12 August 2019 15:44 > To: [email protected] > Subject: [PSES] GTEM cell used for RE measurement > > Does anyone out there have a simple transducer factor that yields rf > potential at the GTEM cell vertex coaxial connector for a given vertical > electric field component coupling to the cell septum? Purpose is to calculate > gain/noise figure specs for a preamplifier used between spectrum analyzer and > GTEM cell to measure RE. > > Thank you. > > Ken Javor > Phone: (256) 650-5261 > > > - > ---------------------------------------------------------------- > 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]> <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) <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]> > Mike Cantwell <[email protected]> > > > For policy questions, send mail to: > Jim Bacher <[email protected]> > David Heald <[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) <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]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[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]>
