My instruments are lying to me!!! Or I have used different settings to look at different SSC signals. And like the proverbial bumblebee that was not told he cannot fly because theory says so, these stupid instruments did not read the textbooks. I gotta get a cheaper instrument to see reality. Those R&S boat anchors are ignoring the textbooks. I'm not disagreeing, as much as being disagreeable, ;-), The automotive tests ask for their own criteria in testing. And I remember the automotive days - fondly!
Where, for the first time, I saw those lying instruments show me a QP higher than the Peak. And the instruments were CISPR 16 compliant! Again it was an instrument setting issue - the difference in the spec's that were being tested to! Changing the RBW will give information about the modulation technique, triangle, herseys kiss, digital steps, etc. and will also show different amplitudes depending on conditions. I "assumed" the usual for me. The usual or common, but that depends on what industry is being considered, frequency sweep over time, kinda like dialing a receiver over a frequency range only to find that this SSC noise pops in now and then, to provide a brief moment of interference. The "protected" folks seem to care only about interference in the time domain. They say don't make a chirp in my broadcast! And that happens at any moment in time when the SSC crosses over the licence holders frequency. The automotive guys might be concerned with not deploying the airbags when the SSC crosses over the trigger frequency, or some such situation. Or the sarcastic remark we'd make is that it is broadcasting on all frequencies for everyone's listening enjoyment! ________________________________ From: Ken Wyatt <k...@emc-seminars.com> To: neve...@comcast.net Cc: EMC-PSTC@LISTSERV.IEEE.ORG Sent: Friday, February 10, 2012 2:31 PM Subject: Re: [PSES] Spread-Spectrum Clock Question Hi Neven, I can also confirm that you should see a decrease in amplitude in peak mode for SS clocking. I use my simple handheld Thurlby Thander PSA2701T peak-reading spectrum analyzer to demo this during my EMC seminars. _______________________ Kenneth Wyatt Wyatt Technical Services LLC Woodland Park, CO Email Me! | Web Site | Blog Subscribe to Newsletter Connect with me on LinkedIn On Feb 10, 2012, at 12:16 PM, Neven Pischl wrote: I would like to thank sincerely to all who responded, I appreciate it. I am not going to react to any discussions on whether it is cheating or not :), it was not anywhere in my mind when I posted the question and I hope this topic does not degrade :). > >But, I'd like to summarize a little: > >1. I do care about the Pk measurements, not only about QP and Avg, because >that is in the specs I am dealing with (some automotive emission requirements) > >2. I found out, as I suspected and was confirmed in some replies, that if I >change the modulating frequency up to over 20 kHz, then I see reduction with >100/120kHz RBW also, not only with 1kHz RBW. Hence, there is an effect of the >modulating frequency and the RBW combination on the measured Pk results. > >3. SSC by using frequency modulation of the clock actually does reduce the >peak value. I have seen some replies saying it does not, and over many years I >have come across people who said the same. However, if you look in any >textbook on FM, you can see that - in the frequency domain - FM causes the >power of the carrier to be distributed into the side-bands, with the total >power the same with or without the modulation. Therefore, because the power >power stays the same, it must be that each of the components in the spectrum, >i.e. the carrier and the two side-lobes, must have a lower amplitude than the >unmodulated carrier. Please, do not confuse the individual amplitudes of >individual spectral components with the amplitude of the signal in the >time-domain, which indeed stays the same. > >In case of a digital pulses, the "carrier" is the fundamental as well as each >of the harmonics. > >Because of the above, and if you look with the infinitely small RBW (i.e. do >the math), SSC does indeed reduce the peak value of each harmonic (and >fundamental). BTW, the "speed" or modulating freqeuncy does not have a bearing >on the level of reduction of the peak values, in such an ideal case. Only the >modulatioin index (similar to "depth") is important, as it defines how much >power of the carrier is put into the side-lobes. > >The issue I was facing was that under the test conditions of the EMC >specification I have to use a specified "wide" RBW. Under that condition, the >modulating frequency is important too - as I found out. > > >Best regards to all, > >Neven- >---------------------------------------------------------------- > >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>
