Like they say in some movies…”follow the money”. In the case of EMC issues, it’s usually “follow the current”. Both differential and common mode currents want to return to their sources in the most expedient (low-impedance) route. If designers fail to define a return path, invariably, some of that RF current radiates. Once the noise source(s) are identified, then what’s the return path? There will always be a return path…just not always the one you want.
Cheers, Ken _______________________ I'm here to help you succeed! Feel free to call or email with any questions related to EMC or EMI troubleshooting - at no obligation. I'm always happy to help! Kenneth Wyatt Wyatt Technical Services LLC 56 Aspen Dr. Woodland Park, CO 80863 Phone: (719) 310-5418 Email Me! <mailto:[email protected]> | Web Site <http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/> The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog> Subscribe to Newsletter <http://www.emc-seminars.com/Newsletter/Newsletter.html> Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt> > On Jun 28, 2017, at 11:35 AM, Ralph McDiarmid > <[email protected]> wrote: > > Rather than 'ground', perhaps 'RF return' or 'counterpoise' might be better > terms? > > I think the thing that makes EMC mysterious is that the complete RF circuit > is unseen and difficult to accurately define, given all the parasitic > elements. The experience of 'inside' verses 'outside' the chassis envelope a > prime example, something I encountered some years ago, but never fully > understood. > > Ralph McDiarmid > Product Compliance > Engineering > Solar Business > Schneider Electric > > > -----Original Message----- > From: Bill Owsley [mailto:[email protected] > <mailto:[email protected]>] > Sent: Saturday, June 24, 2017 8:33 PM > To: [email protected] <mailto:[email protected]> > Subject: Re: [PSES] USB dongle connector shield filtered grounding > > Ancient EMC mythology, well proven to be wrong and so abandoned decades ago. > And still it pops on occasion and often with new twists to revive the > mythology.So it gets ignored as those new to the stories, such that they > cannot figure it out, will need the lessons of 'on the job training'. > ps. the proper terminology needed to clearly enunciate the concepts is not > settled. > The physics is plain and simple but to describe it takes a lot words due to a > lack of commonly understood terminology. > For example 'ground' serves as the catchall term, for shielding, signal > return, power return, zero reference, analog return, digital return, chassis, > circuit, logic, cable, AND for Safety as in earth ground. > Now Maxwell's law's (made up by a mad Scotman back in the 1800's) dictate > that a so-called signal must be accompanied by its return signal, and further > more that return signal will couple as close as possible to the original > so-called signal. The two parts are inextricably intertwined and cannot be > considered separately, without great risk to ones grasp of reality. Just as > the alleged E-field and H-field are two aspects of the same thing, which > conveniently might be called the Poynting Vector, and are related by the > Impedance, the ratio of the two fields, which in free space, well away from > any conducting structures, is approximately 377 ohms. > > Now conducting structures, ones like a circuit 'ground', a chassis 'ground', > a shielding 'ground' and signal returns often called 'ground' and the concept > of 'inside' verses 'outside' which seems to ignore Maxwell, are all going to > make for a rich realm of mythology which is not well defined and so, all > sorts of imaginings are created to fill all the constructed voids from using > all these artificial concepts, when one simple concept is necessary and > sufficient to complete the structure. > > Aside: If that secret, the simple one, was to be 'leaked' to common > knowledge, we all would be out of a job in managing EMC since even the simple > digital guys could understand it. So we keep it under-wraps and obscure by > using mysterious language so that the neophytes and uninitiated think that > they understand and/or have no clue as to what is going on. > > Always the correct answer: "It depends!"- Bill > > > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > ______________________________________________________________________ > > - > ---------------------------------------------------------------- > 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]> - ---------------------------------------------------------------- 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]>
