It really depends on the impedance of the wire or cable it’s clamped around. If the impedance is low, compared to the ferrite Z, then you’ll get some benefit. If it’s high, for example, 100 Ohms, then a 100 Ohm ferrite won’t do anything.
A good reference is Würth Electronics, Trilogy of Magnetics, which I reviewed some time ago on The EMC Blog: http://www.edn.com/electronics-blogs/emc-emi-rfi-esd/4395583/Review--Trilogy-of-Magnetics-by-W-rth-Electronics <http://www.edn.com/electronics-blogs/emc-emi-rfi-esd/4395583/Review--Trilogy-of-Magnetics-by-W-rth-Electronics> The basic equation is: Attenuation = 20log((Zin + Zferrite + Zload)/(Zin + Zload)), where Zin is the impedance of the interfering source and Zload is the impedance of the interfering load. Cheers, Ken _______________________ Kenneth Wyatt Wyatt Technical Services, Inc. 56 Aspen Dr. Woodland Park, CO Phone: (719) 310-5418 Email Me! <mailto:k...@emc-seminars.com> | 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 Mar 3, 2015, at 10:38 AM, Grasso, Charles <charles.gra...@echostar.com> > wrote: > > Hello all, > > It is generally reported (at least as far as I can remember) that a ferrite > bead clamped on a cable > will provide – typically- only about 3db of improvement as a general rule. I > am now in a position > of looking for the source of that “common knowledge” .. Does anyone have > such a reference? > > Best Regards > Charles Grasso > Compliance Engineer > Echostar Communications > (w) 303-706-5467 > (c) 303-204-2974 > (t) 3032042...@vtext.com <mailto:3032042...@vtext.com> > (e) charles.gra...@echostar.com <mailto:charles.gra...@echostar.com> > (e2) chasgra...@gmail.com <mailto:chasgra...@gmail.com> > > - > ---------------------------------------------------------------- > 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 <mailto:emc-p...@ieee.org>> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > <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/ > <http://product-compliance.oc.ieee.org/> can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ <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 > <http://www.ieee-pses.org/listrules.html> > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org>> > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org>> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org>> > David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com>> > - ---------------------------------------------------------------- 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>
