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>
