There are two reasons for spread spectrum techniques. One contributed to by the lady movie star, for avoiding detection and interference and which is used by all sorts of digital communications today as directed by several standards. The other, patented by IBM, is used deliberately to reduce QP measurements within the QP defined parameters of nominally steady state emissions, such as a clock. The second was originally implemented in an analog fashion using a version of FM, as in radio. The not so famous "hershey kiss" shape for time spend per frequency unit. The first was done digitally jumping among a list of random frequencies for brief moments. A hybrid came about with analog FM being implemented digitally by a list of frequencies describing a type of shape over time.
A common interpretation by a test house is looking at the peak hold of a QP detector over time and frequencies and comparing to the limits. However, a QP measurement is done at single frequencies, each one individually, at the defined BW, and time dwell. ps. if the excursion over the limit is seldom, rarely, an argument that it is a "click" can used. Some devices have a brief overshoot when jumping among frequencies. Get another device, but by time this is discovered, one may be somewhat committed to that device. That sucks. A "hershey kiss" shape will give a flat top smooth shape on the peak or QP hold detector. Analog FM will give a smooth shaped top where a digital modulation will give an indication of the individual frequencies in the list by the bumpy top. A common appearance of any mod but the "hershey kiss" looks like batman ears. The frequency high and low ends of the modulation will be a bit higher than the middle due to added dwell time within the BW. Those two ears are often the failing frequencies. Now all the debating and teeth gnashing begin. Remember it is the manufacturer, not the test house, that is responsible. And here is a real life story. Long ago, worked on a system that operated at 58 kHz +/- 200 hertz with about 15 kW of energy.Was informed by an outside agency, that it was well over the limit around 5.8 GHz. Never previously measured there as not required nor anticipated. Put the system in a reverb chamber with the receiver, detector in the diagonal corner. Saw nothing initially. BUT on peak hold and a long scan, overnight, some measurements over the limit were detected. Eventually the bandwidth detected displayed an amazing range of frequencies for nominal 400 hz. The combination of brief transmissions with the scan rate of the spec an, made detection rather rare. Asked agency what standard is required to meet? No answer. They went away. On Tuesday, December 7, 2021, 2:21:43 AM EST, Amund Westin <am...@westin-emission.no> wrote: Thanks guys. I checked out the actual case yesterday and was told that the reason for observing QP for a longer time was that the product had used a spread spectrum technique. Best regards Amund Fra: Paasche, Dieter Sendt: 6. desember 2021 16:35 Til: EMC-PSTC@LISTSERV.IEEE.ORG; Amund Westin <am...@westin-emission.no> Emne: RE: [PSES] Max Hold Quasi-peak ? Hi, I agree with the statements mentioned. It depends on the nature of the disturbance and you would have to find out what is happening during that period of time. I would also suggest to review CISPR 16-2-1, specifically to the definition of continuous disturbance. Section 3 continuous disturbance RF disturbance with a duration of more than 200 ms at the IF-output of a measuring receiver, which causes a deflection on the meter of a measuring receiver in quasi-peak detection mode which does not decrease immediately Section 6.5 Interpretation of measuring results. 6.5 Interpretation of measuring results 6.5.1 Continuous disturbance The following steps shall be applied when interpreting the results for continuous disturbance measurements: a) At each frequency for which the level of disturbance is close to the limit and not steady, the reading on the measuring receiver is observed for at least 15 s for each measurement; the highest readings shall be recorded. Some product standards allow the exclusion of isolated clicks, which shall be ignored (e.g. CISPR 14-1). There are more conditions in this sections. Sincerely, | | | | | | Dieter Paasche Senior Product Developer Electrical / EMC Compliance | | | dieter.paas...@christedigital.com Work: (519) 744-8005 Ext. 7211 www.christiedigital.com | | | 809 Wellington St. N. Kitchener, Ontario N2G 4Y7 Canada | | This e-mail message (including attachments, if any) is confidential. Any unauthorized use, distribution or disclosure is prohibited. If you have received this e-mail message in error, please notify the sender by reply e-mail or telephone and delete it and any attachments from your computer system and records. From: Charles Grasso <charles.gra...@dish.com> Sent: Monday, December 06, 2021 10:08 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Max Hold Quasi-peak ? | | CAUTION:This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe. | Interesting topic! Completely agree with Brent!. I would only add the "quality" of the signal can also contribute to the variation - by that I mean if there is any kind of modulation on the signal then that will contribute to the measurement difficulties. It is also not unusual for a lab to sit on a signal if the signal has a noted time variance (this is from experience). On Sun, Dec 5, 2021 at 11:46 AM Amund Westin < wrote: This message originated outside of DISH and was sent by: owner-emc-p...@listserv.ieee.org Some weeks ago I went to a test lab as an observer on a CE marking project (IT product). I participated on the radiated emission testing and some frequencies were above the limit line during the scan (peak measurement). Later on, the Quasi-Peak measurement lowered the values significant and therefore with the result Passed. Later on, I was told that they continued the testing by 10-15 minutes and was logging the maximum Quasi Peak value (repetitive QP meas) on spike with the highest value. During these 15 minutes, one or two QP measurement was above the limit and the result was changed from Passed to Failed. I have not seen this test procedure before. I’m familiar with just one QP measurement on each frequency and not Max Hold QP on each for 10-15 minutes. Anyone who have experienced the same? Is it a CISPR procedure or just some overzealous lab engineers? Best regards Amund - ---------------------------------------------------------------- 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> -- Charles Grasso Dish Technologies (c) 303-204-2974 (h) 303-317-5530 (e ) charles.gra...@dish.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://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> - ---------------------------------------------------------------- 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> - ---------------------------------------------------------------- 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>