Hi Ken/Chas, I forwarded your Q&A to a consultant friend of mine who specializes in wireless and co-existance, Dr. Robert Morrow. Here's his comments.
802.11b has a bandwidth of around 22 MHz, and the slower data rates of 1 and 2 Mb/s have some spread spectrum processing gain (about 10 dB) that can cut the effect of jamming signals. The 5.5 and 11 Mb/s data rates don't have much processing gain but the receivers are usually pretty good about rejecting interference and the 802.11 network can always drop to the lower speeds if necessary. 802.11g has a bandwidth of about 17 MHz, and as long as a harmonic isn't hitting one of the four pilot frequencies they usually perform well because a few of the jammed subcarriers can be recovered via error correction. Also, 802.11g can drop to 802.11b speeds in situations of poor channel conditions. Newer 802.11n works the same way with automatic backoff to lower data rates of 802.11g and 802.11b if necessary, and it can also operate in both the 2.4 and 5 GHz bands. The very latest 802.11ac that's showing up in computers today operates in the 5 GHz band only. When the interfering signal is of a different structure than the desired signal to be analyzed, the only sure way to test performance is empirical, either over-the-air or via cables and attenuators. Hope this helps, Ken _______________________ Kenneth Wyatt Wyatt Technical Services LLC 56 Aspen Dr. Woodland Park, CO Phone: (719) 310-5418 / Toll Free: (877) 443-9275 Email Me! | Web Site | Blog The EMC Blog (T&M World) Subscribe to Newsletter Connect with me on LinkedIn On Aug 30, 2013, at 9:27 AM, Ken Javor wrote: > Just some basic observations. In order for a dithered clock to solve a > regulatory problem, the frequency shift must be greater than the measurement > bandwidth. In order for the dithered clock to solve an EMI problem, the > frequency shift must be larger than the potential victim’s bandwidth. > > In an ideal world, the measurement and victim BW are the same. This is > realized, for instance, in the FM BCB, but not in the television bands. > > So the immediate question is what is a WiFi channel BW, relative to the 1 MHz > (?) BW of the CISPR measurement above 1 GHz. The WiFi BW is considerably > larger than 1 MHz in order to support download speeds these days, so it is > quite possible for a dithered clock to push the frequency outside the > measurement BW but still remain in the WiFi channel, where it can cause > mischief. > > Ken Javor > Phone: (256) 650-5261 > > > From: "Grasso, Charles" <charles.gra...@echostar.com> > Date: Fri, 30 Aug 2013 14:39:15 +0000 > To: "emc-p...@ieee.org" <emc-p...@ieee.org> > Conversation: Spread Spectrum clocking and adverse WIFI effects > Subject: Spread Spectrum clocking and adverse WIFI effects > > Hello all, > > Spread spectrum clocking has a *wonderful* effect on radiated emissions > especially DDR generated noise. > > My question is: Given the high degree of integration in today’s products: > > Does anyone have concrete experiences of degraded WiFi performance as a > result of using SSC? > > Best Regards > Charles Grasso > Compliance Engineer > Echostar Communications > (w) 303-706-5467 > (c) 303-204-2974 > (t) 3032042...@vtext.com > (e) charles.gra...@echostar.com > (e2) 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> > > 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://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <emcp...@radiusnorth.net> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <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://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > For help, send mail to the list administrators: > Scott Douglas <emcp...@radiusnorth.net> > Mike Cantwell <mcantw...@ieee.org> > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <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://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
