When I think of how well a simple AVC circuit in an AM radio receiver works, I assumed that an extension of that would serve well as a QP filter (with TC for both charge and discharge) If the tuned signal fell within the range of the IF amplifier string, I thought that would have been enough protection against saturation and overload effects. _______________________________________ _____________________________________________
Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Compliance Engineer From: Ralph McDiarmid/Canada/Schneider To: EMC-PSTC@LISTSERV.IEEE.ORG List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: 03/24/2010 10:26 AM Subject: Re: the QP detector ________________________________ Thanks to John, Michael, Robert and Ken for shedding some light on a topic which I suspect many of the rest of us don't understand as well as we would like. It seems like such a simple option to the detector of an EMI receiver or spectrum analyser, I'm surprised it's not found in all of them. _______________________________________ _____________________________________________ Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Compliance Engineer From: John Woodgate <j...@jmwa.demon.co.uk> To: EMC-PSTC@LISTSERV.IEEE.ORG List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: 03/23/2010 02:26 PM Subject: Re: [PSES] the QP detector ________________________________ In message <OF055749D9.17851873-ON882576EF.00699E5B-882576EF.0069F5B7@US.Schneider-E lectric.com>, dated Tue, 23 Mar 2010, ralph.mcdiar...@ca.schneider-electric.com writes: >Here is a link to an interesting historical note on the Quasi-peak >Detector. Hopefully, someone on this forum can answer one or more of >the questions at the end of the article to enlighten the rest of us. > >http://www.ieee.org/organizations/pubs/newsletters/emcs/summer01/pp.bron <http://www.ieee.org/organizations/pubs/newsletters/emcs/summer01/pp.bron> >augh.htm Well, Ed Bronaugh was much closer to the early development than I, but I may throw in a few points, without claim of correctness. 1.Who actually designed the first QP detector and why QP? I don't know who designed it, but I suspect QP was found to correlate best (out of the types of detector tested) with, and this is important, the subjective disturbing effect of the noise on a wanted (audio) programme signal. This is certainly true for the ITU BS468-4 noise meter. 2. For many years CISPR QP and ANSI QP were different. How did this happen and why was the ANSI QP dumped in favor of the CISPR QP? I suspect that the CCIF (as it was then) also studied the subject and influenced the outcome. 3. How were the charge and discharge time constants selected for the first QP detectors and why were they changed over the years? See the answer to Q 1. By experiment. How was the bandwidth selected? [Note: the 9 kHz bandwidth was the prevalent bandwidth of radio receivers for sound broadcast reception at the time. EdB] Indeed. 4. The dynamic range of the first CISPR meters was less than 15 dB, whereas the first Stoddart meters had a dynamic range of 40 dB. Why did the CISPR meter have this limitation and how did Stoddart get around it? Again, I suspect that the first meter design was barely adequate to cover a subjective range from 'just about acceptable' to 'unusable'. For AM radio, a range of around 26 dB is necessary to accommodate the ITU-R 'not perceptible' bound. I know nothing of Stoddart, but a second design is often much better than a first one. For example, in search of more dynamic range in the 1930s, one might choose battery operation to eliminate mains hum 4. Who put together this first board of listeners? What were they asked to do and what meters with what detectors were used in this work? I guess they were asked to listen to different audio programmes with different levels of interference superimposed, and compare meter readings in some way with their subjective assessments, perhaps on a 5-point scale. The detectors would have been all that could be made at that time, rectified average, approximate r.m.s. and QP - device limitations would have made true peak (e.g. 10 us response time) difficult. These detectors would operated on the **audio** signal, not the carrier. Was the QP detector really designed as a result of this work? Almost certainly. 5. When CISPR extended the QP technique to a broader range of frequencies, how did they come up with the time constants in this meter since they are not the same as the time constants for the lower frequency meter? Probably related to the increased measurement bandwidth at higher frequencies. There is an interesting PDF of a Power Point presentation, including relatively recent developments, at: resource.npl.co.uk/docs/networks/.../071129/cispr.../medler.pdf - 6. What about the T&D Committee of the IEEE PES "board of listeners" that evaluated TV reception in the presence of power line interference several years ago? Who knows? With the proliferation of communication systems, one could easily ask if any single detector can adequately predict the interference effect of all the various disturbances on all the various communications systems. See the Medler paper for a discussion of that. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK I should be disillusioned, but it's not worth the effort. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com>
