Re: Q on Correlation of Votage ripple with a Spectrum Analyser
Mr. Novak makes some excellent points. I was under the assumption that the phrase voltage ripple implied conducted emission measurements at a LISN port. Hence my comments on mode separation. Across a spectrum of even 30 MHz, any normal scope probe I know of (1 or 10 M Ohm in parallel with 5/10/20 pF) will present a varying load to the measured waveform. I know there are some broadband active differential probes with low shunt capacity, but I have no experience using them. The scope should be made to look like a flat 50 Ohm load to help correlate to a spectrum analyzer. Instead of using long leads to make measurements from one point of the Vcc plane to another, I would make coaxial measurements from one point on the Vcc plane to chassis ground or the reference/image plane if one exists, and then make the same measurement at another point on the Vcc plane, and compare the waveforms, perhaps using a built-in math function if your scope has that. Of course this technique requires the reference/image plane/chassis ground to be an equipotential plane... By coaxial measurement I mean using coax rather than a scope probe, and terminating the shield at the reference point, while extending the center conductor just far enough to connect to the point of interest on the Vcc plane. Theoretically, an even better technique would be to have a place on the board where the power plane reference was available circumferentially around a Vcc via, and connect the coax shield to the reference plane and the center conductor to the Vcc contact. Given a 50 Ohm load at the other end (with a blocking cap to protect it), and an FFT capability with enough memory, I believe you could achieve correlation with the individual spectral components measured by a spectrum analyzer (which of course would also need a blocking cap with this config). From: istvan novak istvan.no...@worldnet.att.net Date: Sun, 27 Jul 2003 11:02:02 -0400 To: Charles Grasso cgrassospri...@earthlink.net, Ken Javor ken.ja...@emccompliance.com, Emc-Pstc emc-p...@ieee.org Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware today is so complex that you cant predict for sure its activity; it is a strong function of time. -tThe spectrum analyzer and scope will look at the same signal in different ways: analog spectrum analyzers have a seep time and settling time determining the frequency and aperture of visit each frequency. If you have a spectrumn analyzer used for compliance tests, probably the CISPR filter is on. Scopes on the other hand (digital scopes) undersample the signal, whether it is called real-time or not. Memory and displey refresh rate does not allow scopes to display and process all data points of high-frequency signals. Real-time scopes do it for a given time window, but it is usually way less than the time constant of a CISPR filter on the spectrum analyzer. - connection to the source makes a big difference. I assume when you calibrated the reading with a sine wave, a coaxial cable with coax connectors at both ends was used. Presumably the product does not have a coaxial connector on the Vcc plane, so you have to make your own connection or use a hand-held probe. This is very extra noise usually gets in the path, and the scope reading becomes unrealistically high. I have found no active scope probes so far, which would give a correct reading in a noisy environment. We hopefully should not see noise on the Vcc planes more than a few hundred mV. In contrast, many scope probes can pick up spikes as big as volts from the environment. If you want to measure noise levels below 100mVpp, double-shielded coax is necessary in noisy environments. Here the 'noisy environment' refers to the close vicinity of the point you test. The simplest test is: take your present probe, and hook up a good double-shielded coax to the same points. Check both readings on the same scope at the same time, and compare. I hope this helps. Best regards, Istvan Novak SUN Microsystems - Original Message - From: Charles Grasso cgrassospri...@earthlink.net To: Ken Javor ken.ja...@emccompliance.com; Emc-Pstc emc-p...@ieee.org Sent: Saturday, July 26, 2003 9:11 PM Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser Hi all, Actually I was using a good ole Spectrim Analyser so I sidestepped the windowing issue/software issues altogether. What I was(am)trying to do was match the max voltage as measured on a scope with the value as measured on a SA. I first calibrated myslef using a known source - a sine wave. The amplitudes fell in just as theory predicted. Encouraged, I then probed the Vcc plane on a product I was working on and was not so happy!! Any ideas? -Original Message- From:
Re: pulse modulation in reverb chambers
So if I am worried whether the 1 us pulse width can be sustained, and I don't know how to determine it analytically, my plan is as follows: I put a wire probe in the room, run it to a spectrum analyzer tuned to the transmit frequency, put the analyzer in zero span mode with a 1 or 3 MHz bandwidth and look at the modulation waveform. If it is significantly longer than 1 us, I know my constructive interference path delays are smearing the modulation away. Comments yea or nay? And thanks for all comments so far! From: John Woodgate j...@jmwa.demon.co.uk Reply-To: John Woodgate j...@jmwa.demon.co.uk Date: Sun, 27 Jul 2003 07:36:15 +0100 To: emc-p...@majordomo.ieee.org Subject: Re: pulse modulation in reverb chambers I read in !emc-pstc that Ken Javor ken.ja...@emccompliance.com wrote (in bb48596e.36a1%ken.ja...@emccompliance.com) about 'pulse modulation in reverb chambers' on Sat, 26 Jul 2003: What is the limitation on minimum pulse width in reverberation chambers? I expect it relates to room size, but does anyone have either a functional relation or a rough order of magnitude? Light travels 300 meters per microsecond, so I would think a 1 microsecond pulse width would work just fine, but nanosecond rise-times would be lost. Judging by what happens a million times slower in acoustics, I think 1 microsecond could be quite a bit short. Obviously it depends on the size of the chamber. If there is a paddle, it might be necessary to allow several turns of it to establish a cyclically stable field pattern. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
Zero span can show rep rate or modulation but it cannot correlate the MHz bandwidth waveform amplitude the scope sees with the amplitude of any particular spectral component to which the spectrum analyzer is tuned. Further, the spectrum analyzer is a much more sensitive device than the scope, and it typically has about 80 dB of on screen dynamic range, whereas an 8 bit oscilloscope has 48 dB of dynamic range. From: Cortland Richmond 72146@compuserve.com Reply-To: Cortland Richmond 72146@compuserve.com Date: Sat, 26 Jul 2003 20:45:18 -0400 To: Charles Grasso cgrassospri...@earthlink.net, ieee pstc list emc-p...@ieee.org Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser Charles Grasso wrote: What I was(am)trying to do was match the max voltage as measured on a scope with the value as measured on a SA. Try zero span on the SA. Compare THAT with the scope. Cortland --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
As I mentioned earlier, the waveform from a switching power supply has two distinct components, due to the fast rise-time driving current into ground (common mode) and the pulse itself which is differential mode. Separating modes allows you to time window properly to really resolve the waveform to be FFT'd. In my experience, that makes a world of difference. To specify further, I had maybe 32 k of memory. If you have infinite memory, you can FFT a 10 us pulse with a sub-microsecond rise-time, but with limited memory, you get better results doing a separate FFT on the rise-time and then the pulse. From: John Woodgate j...@jmwa.demon.co.uk Reply-To: John Woodgate j...@jmwa.demon.co.uk Date: Sun, 27 Jul 2003 07:46:29 +0100 To: emc-p...@majordomo.ieee.org Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser I read in !emc-pstc that Charles Grasso cgrassospri...@earthlink.net wrote (in ekeeipjkkmpklafoobmcoelhcfaa.cgrassospri...@earthlink.net) about 'Q on Correlation of Votage ripple with a Spectrum Analyser' on Sat, 26 Jul 2003: Has anyone tried correlating the voltage ripple as seen on a scope with the amplitudes measured on a Spectrum Analyser? More information, please. What voltage is it that has ripple on it? Do you mean the ripple voltage across a rectifier filter capacitor? I tried doing that the other day with ..umm. minimal success. I think that due to the comples convoltions that would have to occur when FFT'ing an irregular voltage shape. It's really no more difficult to FFT one waveform than another. The FFT doesn't 'know' whether the waveform looks regular or irregular to a human. If it is power supply ripple that you are considering, the waveform is approximately a sawtooth, but the short rising branch is a small section of the crest of a sine wave. If the ripple voltage is very small compared with the d.c. voltage and the ESR of the filter capacitor is very low, the spectrum of the ripple is often quite close to that of a sawtooth. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware today is so complex that you cant predict for sure its activity; it is a strong function of time. -tThe spectrum analyzer and scope will look at the same signal in different ways: analog spectrum analyzers have a seep time and settling time determining the frequency and aperture of visit each frequency. If you have a spectrumn analyzer used for compliance tests, probably the CISPR filter is on. Scopes on the other hand (digital scopes) undersample the signal, whether it is called real-time or not. Memory and displey refresh rate does not allow scopes to display and process all data points of high-frequency signals. Real-time scopes do it for a given time window, but it is usually way less than the time constant of a CISPR filter on the spectrum analyzer. - connection to the source makes a big difference. I assume when you calibrated the reading with a sine wave, a coaxial cable with coax connectors at both ends was used. Presumably the product does not have a coaxial connector on the Vcc plane, so you have to make your own connection or use a hand-held probe. This is very extra noise usually gets in the path, and the scope reading becomes unrealistically high. I have found no active scope probes so far, which would give a correct reading in a noisy environment. We hopefully should not see noise on the Vcc planes more than a few hundred mV. In contrast, many scope probes can pick up spikes as big as volts from the environment. If you want to measure noise levels below 100mVpp, double-shielded coax is necessary in noisy environments. Here the 'noisy environment' refers to the close vicinity of the point you test. The simplest test is: take your present probe, and hook up a good double-shielded coax to the same points. Check both readings on the same scope at the same time, and compare. I hope this helps. Best regards, Istvan Novak SUN Microsystems From: Charles Grasso cgrassospri...@earthlink.net To: Ken Javor ken.ja...@emccompliance.com; Emc-Pstc emc-p...@ieee.org Sent: Saturday, July 26, 2003 9:11 PM Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser Hi all, Actually I was using a good ole Spectrim Analyser so I sidestepped the windowing issue/software issues altogether. What I was(am)trying to do was match the max voltage as measured on a scope with the value as measured on a SA. I first calibrated myslef using a known source - a sine wave. The amplitudes fell in just as theory predicted. Encouraged, I then probed the Vcc plane on a product I was working on and was not so happy!! Any ideas? -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Saturday, July 26, 2003 4:19 PM To: Charles Grasso; Emc-Pstc Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser I presented a paper on that very subject about a decade ago at one of the EMC TD magazine EMC symposia. I used a Fluke Scopemeter and some FFT software that came with it. The Fluke interfaced to the PC through an optically isolated RS-232 protocol. It worked quite well from a pre-compliance or troubleshooting point-of-view. You could use time windowing to separate the signals deriving from leading and falling edges from the signals deriving from the pulse itself. I used LISNMATE and LISNMARK mode separation devices to show that the rising/falling edge signals were common mode, while the pulse itself generated differential mode signals. From: Charles Grasso cgrassospri...@earthlink.net Reply-To: Charles Grasso cgrassospri...@earthlink.net Date: Sat, 26 Jul 2003 16:18:36 -0700 To: Emc-Pstc emc-p...@ieee.org Subject: Q on Correlation of Votage ripple with a Spectrum Analyser Hi All, Has anyone tried correlating the voltage ripple as seen on a scope with the amplitudes measured on a Spectrum Analyser? I tried doing that the other day with ..umm. minimal success. I think that due to the comples convoltions that would have to occur when FFT'ing an irregular voltage shape. Charles Grasso Echostar Communications. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
I read in !emc-pstc that Charles Grasso cgrassospri...@earthlink.net wrote (in ekeeipjkkmpklafoobmcaelkcfaa.cgrassospri...@earthlink.net) about 'Q on Correlation of Votage ripple with a Spectrum Analyser' on Sat, 26 Jul 2003: I first calibrated myslef using a known source - a sine wave. Really? You calibrated yourself? The amplitudes fell in just as theory predicted. Encouraged, I then probed the Vcc plane on a product I was working on and was not so happy!! You really must write more clearly, and give much more information, if you want useful answers. What did you find that made you unhappy? Maybe we can tell you where it came from. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
I read in !emc-pstc that Charles Grasso cgrassospri...@earthlink.net wrote (in ekeeipjkkmpklafoobmcoelhcfaa.cgrassospri...@earthlink.net) about 'Q on Correlation of Votage ripple with a Spectrum Analyser' on Sat, 26 Jul 2003: Has anyone tried correlating the voltage ripple as seen on a scope with the amplitudes measured on a Spectrum Analyser? More information, please. What voltage is it that has ripple on it? Do you mean the ripple voltage across a rectifier filter capacitor? I tried doing that the other day with ..umm. minimal success. I think that due to the comples convoltions that would have to occur when FFT'ing an irregular voltage shape. It's really no more difficult to FFT one waveform than another. The FFT doesn't 'know' whether the waveform looks regular or irregular to a human. If it is power supply ripple that you are considering, the waveform is approximately a sawtooth, but the short rising branch is a small section of the crest of a sine wave. If the ripple voltage is very small compared with the d.c. voltage and the ESR of the filter capacitor is very low, the spectrum of the ripple is often quite close to that of a sawtooth. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: pulse modulation in reverb chambers
I read in !emc-pstc that Ken Javor ken.ja...@emccompliance.com wrote (in bb48596e.36a1%ken.ja...@emccompliance.com) about 'pulse modulation in reverb chambers' on Sat, 26 Jul 2003: What is the limitation on minimum pulse width in reverberation chambers? I expect it relates to room size, but does anyone have either a functional relation or a rough order of magnitude? Light travels 300 meters per microsecond, so I would think a 1 microsecond pulse width would work just fine, but nanosecond rise-times would be lost. Judging by what happens a million times slower in acoustics, I think 1 microsecond could be quite a bit short. Obviously it depends on the size of the chamber. If there is a paddle, it might be necessary to allow several turns of it to establish a cyclically stable field pattern. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Last day of manufacture EN60950: A4, A11
Ilan, The date of cessation as given in the Official Journal of the European Communities is not the last date for modifications but the last date on which a statement of compliance to a particular version of a standard offers a presumption of compliance with the safety objectives of the LVD (and the essential requirements of the RTTED, where applicable). If a manufacturer wishes to base their compliance with the LVD or RTTED on the fact that they comply with a certain version of a Harmonised Standard (EN60950 +A1 +A2 +A3 + A4 + A11 in your case) then the date of cessation effectively becomes last date of manufacture. Beyond the date of cessation the manufacturer either has to declare compliance with the safety objectives [essential requirements: RTTED] directly or they will have had to have had their product evaluated against a more recent version of the standard: they will also have had to update their Declaration of Conformity and Technical File accordingly. Regards, Richard Hughes Safety Answers Ltd.
Re: pulse modulation in reverb chambers
Sorry, but I don't understand the physics here. Could you please explain how a 10 us delay could add 0.01 us to a 1 us pulse? A typical pulse rep rate is 1 kHz. To me it seems that a 10 us delay would cause no interference effect at all, since the first pulse is over and another isn't due to arrive for another millisecond. What you said makes sense to me if you meant 10 ns, but that is not what your message said. Was that a typo? From: John Woodgate j...@jmwa.demon.co.uk Reply-To: John Woodgate j...@jmwa.demon.co.uk Date: Sun, 27 Jul 2003 21:20:07 +0100 To: emc-p...@majordomo.ieee.org Subject: Re: pulse modulation in reverb chambers I read in !emc-pstc that Ken Javor ken.ja...@emccompliance.com wrote (in bb4987fa.372a%ken.ja...@emccompliance.com) about 'pulse modulation in reverb chambers' on Sun, 27 Jul 2003: As long as those delays are much shorter than 1 us (path difference much less than 300 meters), the original modulation is received. Not really. If a reflection arrives with a delay of 10 us, the received pulse is 1.01 us long. Some 'rays' suffer multiple reflections, which increases the delay considerably, and the reflections in a reverberation chamber must be low-loss. How much stretching can you accept? This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
Charles, Instead of using the 1GHz single-ended scope probe, have you tried to connect the same coax cable that you made with the seriers 50 ohms for the SA to connect to the scope? With a 50-ohm input impedance setting on the scope, the loading of the planes would be exactly the same. As I mentioned earlier, we checked many scope probes, from Tektronix, Agilent, LeCroy, including some of the new 4-6GHz bandwidth single-ended and differential probes. They all pick up more or less noise from the environment, and not necessarily through the input connection pins or wires. You can take your scope probe, with its input pins open or shorted, and take the infinite persistance scope reading, while you move the probe close to a high-power, high-speed computer board (no connection, just put the probe an inch close). Or, just simply take a desktop light with a transformer in its base, and flip the switch a few times. You will be amased how much noise these probes can pick up through the unshielded (or poorly shielded) front-end amplifier and through the cable connecting to the scope. Best regards, Istvan From: Charles Grasso cgrassospri...@earthlink.net To: Ken Javor ken.ja...@emccompliance.com; istvan novak istvan.no...@worldnet.att.net; Emc-Pstc emc-p...@ieee.org Sent: Sunday, July 27, 2003 4:26 PM Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser This is getting pretty intense for a Sunday!! Both Mr. Javor and Mr Novak make excellent observations. Both center on the method of measurment as a point of concern. To measure the voltage ripple I used a high badwidth (1GHz) sigle ended probe with very short leads. In order to establish the error margin, I used the null experiment technique. (I don't have a diff probe with sufficient bandwidth to hand). I then used a piece of coax with very short leads (just like Mr Javor recommends) and a 50ohm resistor in series with the signal to feed the same voltage ripple to a SA. Clearly there is a voltage division here but thats easily accounted for. My concern is that the impedance of the planes is so much lower than the 50ohm input of the SA and I wanted to match that as much as possible. I belive I have taken care of as much of the measurement problem as possible. Still, the maximum voltages between the two measurments do not come close at all. -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Ken Javor Sent: Sunday, July 27, 2003 10:27 AM To: istvan novak; Charles Grasso; Emc-Pstc Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Mr. Novak makes some excellent points. I was under the assumption that the phrase voltage ripple implied conducted emission measurements at a LISN port. Hence my comments on mode separation. Across a spectrum of even 30 MHz, any normal scope probe I know of (1 or 10 M Ohm in parallel with 5/10/20 pF) will present a varying load to the measured waveform. I know there are some broadband active differential probes with low shunt capacity, but I have no experience using them. The scope should be made to look like a flat 50 Ohm load to help correlate to a spectrum analyzer. Instead of using long leads to make measurements from one point of the Vcc plane to another, I would make coaxial measurements from one point on the Vcc plane to chassis ground or the reference/image plane if one exists, and then make the same measurement at another point on the Vcc plane, and compare the waveforms, perhaps using a built-in math function if your scope has that. Of course this technique requires the reference/image plane/chassis ground to be an equipotential plane... By coaxial measurement I mean using coax rather than a scope probe, and terminating the shield at the reference point, while extending the center conductor just far enough to connect to the point of interest on the Vcc plane. Theoretically, an even better technique would be to have a place on the board where the power plane reference was available circumferentially around a Vcc via, and connect the coax shield to the reference plane and the center conductor to the Vcc contact. Given a 50 Ohm load at the other end (with a blocking cap to protect it), and an FFT capability with enough memory, I believe you could achieve correlation with the individual spectral components measured by a spectrum analyzer (which of course would also need a blocking cap with this config). From: istvan novak istvan.no...@worldnet.att.net Date: Sun, 27 Jul 2003 11:02:02 -0400 To: Charles Grasso cgrassospri...@earthlink.net, Ken Javor ken.ja...@emccompliance.com, Emc-Pstc emc-p...@ieee.org Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
Then the answer is the difference between the sum of all spectral components measured with the scope vs. the individual components themselves. If you want correlation you have to go the FFT route. From a strictly EMC point-of-view only the spectral components matter, the only point of measuring with a scope is if you don't have an analyzer and are going to perform an FFT anyway. From: Charles Grasso cgrassospri...@earthlink.net Date: Sun, 27 Jul 2003 13:26:40 -0700 To: Ken Javor ken.ja...@emccompliance.com, istvan novak istvan.no...@worldnet.att.net, Emc-Pstc emc-p...@ieee.org Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser This is getting pretty intense for a Sunday!! Both Mr. Javor and Mr Novak make excellent observations. Both center on the method of measurment as a point of concern. To measure the voltage ripple I used a high badwidth (1GHz) sigle ended probe with very short leads. In order to establish the error margin, I used the null experiment technique. (I don't have a diff probe with sufficient bandwidth to hand). I then used a piece of coax with very short leads (just like Mr Javor recommends) and a 50ohm resistor in series with the signal to feed the same voltage ripple to a SA. Clearly there is a voltage division here but thats easily accounted for. My concern is that the impedance of the planes is so much lower than the 50ohm input of the SA and I wanted to match that as much as possible. I belive I have taken care of as much of the measurement problem as possible. Still, the maximum voltages between the two measurments do not come close at all. -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Ken Javor Sent: Sunday, July 27, 2003 10:27 AM To: istvan novak; Charles Grasso; Emc-Pstc Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Mr. Novak makes some excellent points. I was under the assumption that the phrase voltage ripple implied conducted emission measurements at a LISN port. Hence my comments on mode separation. Across a spectrum of even 30 MHz, any normal scope probe I know of (1 or 10 M Ohm in parallel with 5/10/20 pF) will present a varying load to the measured waveform. I know there are some broadband active differential probes with low shunt capacity, but I have no experience using them. The scope should be made to look like a flat 50 Ohm load to help correlate to a spectrum analyzer. Instead of using long leads to make measurements from one point of the Vcc plane to another, I would make coaxial measurements from one point on the Vcc plane to chassis ground or the reference/image plane if one exists, and then make the same measurement at another point on the Vcc plane, and compare the waveforms, perhaps using a built-in math function if your scope has that. Of course this technique requires the reference/image plane/chassis ground to be an equipotential plane... By coaxial measurement I mean using coax rather than a scope probe, and terminating the shield at the reference point, while extending the center conductor just far enough to connect to the point of interest on the Vcc plane. Theoretically, an even better technique would be to have a place on the board where the power plane reference was available circumferentially around a Vcc via, and connect the coax shield to the reference plane and the center conductor to the Vcc contact. Given a 50 Ohm load at the other end (with a blocking cap to protect it), and an FFT capability with enough memory, I believe you could achieve correlation with the individual spectral components measured by a spectrum analyzer (which of course would also need a blocking cap with this config). From: istvan novak istvan.no...@worldnet.att.net Date: Sun, 27 Jul 2003 11:02:02 -0400 To: Charles Grasso cgrassospri...@earthlink.net, Ken Javor ken.ja...@emccompliance.com, Emc-Pstc emc-p...@ieee.org Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware today is so complex that you cant predict for sure its activity; it is a strong function of time. -tThe spectrum analyzer and scope will look at the same signal in different ways: analog spectrum analyzers have a seep time and settling time determining the frequency and aperture of visit each frequency. If you have a spectrumn analyzer used for compliance tests, probably the CISPR filter is on. Scopes on the other hand (digital scopes) undersample the signal, whether it is called real-time or not. Memory and displey refresh rate does not allow scopes to display and process all data points of high-frequency signals. Real-time scopes do it for a given time window, but it is usually way less than the
Re: pulse modulation in reverb chambers
That mostly makes sense, except I'm not sure about this part: I'd expect a pulse to excite many modes within a chamber as long as either its length or its transition times are shorter than the time it takes a wave to travel across the chamber and back. That'll smear the pulse. My thinking is just the opposite. The duration of the pulse should be long relative to the time it takes to travel from transmit to receive antennas. Then there is no smearing. I also recall work using network analyzers and time windowing to electronically create an anechoic chamber out of an unlined screen room. From: Cortland Richmond 72146@compuserve.com Date: Sun, 27 Jul 2003 16:44:20 -0400 To: Ken Javor ken.ja...@emccompliance.com, ieee pstc list emc-p...@ieee.org Subject: Re: pulse modulation in reverb chambers Ken, A recent article on reverberant chambers mentions a Q of 83,000 or so. I'd expect a pulse to excite many modes within a chamber as long as either its length or its transition times are shorter than the time it takes a wave to travel across the chamber and back. That'll smear the pulse. On the other hand the FIRST pulse received shouldn't be smeared unless the pulse is longer than the time it takes a reflected wave to arrive at the antenna. If I recall correctly, there've been some papers on time gating to take advantage of this. Cortland This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: pulse modulation in reverb chambers
Ken, A recent article on reverberant chambers mentions a Q of 83,000 or so. I'd expect a pulse to excite many modes within a chamber as long as either its length or its transition times are shorter than the time it takes a wave to travel across the chamber and back. That'll smear the pulse. On the other hand the FIRST pulse received shouldn't be smeared unless the pulse is longer than the time it takes a reflected wave to arrive at the antenna. If I recall correctly, there've been some papers on time gating to take advantage of this. Cortland This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: pulse modulation in reverb chambers
I read in !emc-pstc that Ken Javor ken.ja...@emccompliance.com wrote (in bb4987fa.372a%ken.ja...@emccompliance.com) about 'pulse modulation in reverb chambers' on Sun, 27 Jul 2003: As long as those delays are much shorter than 1 us (path difference much less than 300 meters), the original modulation is received. Not really. If a reflection arrives with a delay of 10 us, the received pulse is 1.01 us long. Some 'rays' suffer multiple reflections, which increases the delay considerably, and the reflections in a reverberation chamber must be low-loss. How much stretching can you accept? But if delays are too long, then the pulse smears. Yes. How long is 'too long' for you? If you can find someone who has ray-tracing software for either electromagnetic **or acoustic** applications, you can run some simulations. Just remember if you use acoustic to treat seconds as microseconds. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Last day of manufacture EN60950: A4, A11
I read in !emc-pstc that Ilan Cohen ico...@itl.co.il wrote (in 2D1037012914D4118DB8204C4F4F502045FE06@ITLLTD01) about 'Last day of manufacture EN60950: A4, A11' on Sun, 27 Jul 2003: Can anyone point me to the specified last day of manufacture for products tested under EN60950: A4 and A11. (In the official Journal you may find the date of 1/08/03 as the last date for modifications, but the last date for manufacture is not listed) I will be very thankful if any one actually points to the official document that specifies the date. The DOCOPOCOSS for a specific standard is given (normally) in the next edition, in this case that is EN 60950:2000. The 'dow' given there is 2005-01-01, and the Commission has not, AFAIK, notified a different DOCOPOCOSS. BUT, there is also EN60950-1:2002, which can be used now and in which the 'dow' of EN 60950:2000 is given as 2006-07-01. You may find it advantageous to use this standard rather than the 2000 edition. DOCOPOCOSS - date of cessation of presumption of compliance of the superseded standard. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Q on Correlation of Votage ripple with a Spectrum Analyser
This is getting pretty intense for a Sunday!! Both Mr. Javor and Mr Novak make excellent observations. Both center on the method of measurment as a point of concern. To measure the voltage ripple I used a high badwidth (1GHz) sigle ended probe with very short leads. In order to establish the error margin, I used the null experiment technique. (I don't have a diff probe with sufficient bandwidth to hand). I then used a piece of coax with very short leads (just like Mr Javor recommends) and a 50ohm resistor in series with the signal to feed the same voltage ripple to a SA. Clearly there is a voltage division here but thats easily accounted for. My concern is that the impedance of the planes is so much lower than the 50ohm input of the SA and I wanted to match that as much as possible. I belive I have taken care of as much of the measurement problem as possible. Still, the maximum voltages between the two measurments do not come close at all. From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Ken Javor Sent: Sunday, July 27, 2003 10:27 AM To: istvan novak; Charles Grasso; Emc-Pstc Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Mr. Novak makes some excellent points. I was under the assumption that the phrase voltage ripple implied conducted emission measurements at a LISN port. Hence my comments on mode separation. Across a spectrum of even 30 MHz, any normal scope probe I know of (1 or 10 M Ohm in parallel with 5/10/20 pF) will present a varying load to the measured waveform. I know there are some broadband active differential probes with low shunt capacity, but I have no experience using them. The scope should be made to look like a flat 50 Ohm load to help correlate to a spectrum analyzer. Instead of using long leads to make measurements from one point of the Vcc plane to another, I would make coaxial measurements from one point on the Vcc plane to chassis ground or the reference/image plane if one exists, and then make the same measurement at another point on the Vcc plane, and compare the waveforms, perhaps using a built-in math function if your scope has that. Of course this technique requires the reference/image plane/chassis ground to be an equipotential plane... By coaxial measurement I mean using coax rather than a scope probe, and terminating the shield at the reference point, while extending the center conductor just far enough to connect to the point of interest on the Vcc plane. Theoretically, an even better technique would be to have a place on the board where the power plane reference was available circumferentially around a Vcc via, and connect the coax shield to the reference plane and the center conductor to the Vcc contact. Given a 50 Ohm load at the other end (with a blocking cap to protect it), and an FFT capability with enough memory, I believe you could achieve correlation with the individual spectral components measured by a spectrum analyzer (which of course would also need a blocking cap with this config). From: istvan novak istvan.no...@worldnet.att.net Date: Sun, 27 Jul 2003 11:02:02 -0400 To: Charles Grasso cgrassospri...@earthlink.net, Ken Javor ken.ja...@emccompliance.com, Emc-Pstc emc-p...@ieee.org Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware today is so complex that you cant predict for sure its activity; it is a strong function of time. -tThe spectrum analyzer and scope will look at the same signal in different ways: analog spectrum analyzers have a seep time and settling time determining the frequency and aperture of visit each frequency. If you have a spectrumn analyzer used for compliance tests, probably the CISPR filter is on. Scopes on the other hand (digital scopes) undersample the signal, whether it is called real-time or not. Memory and displey refresh rate does not allow scopes to display and process all data points of high-frequency signals. Real-time scopes do it for a given time window, but it is usually way less than the time constant of a CISPR filter on the spectrum analyzer. - connection to the source makes a big difference. I assume when you calibrated the reading with a sine wave, a coaxial cable with coax connectors at both ends was used. Presumably the product does not have a coaxial connector on the Vcc plane, so you have to make your own connection or use a hand-held probe. This is very extra noise usually gets in the path, and the scope reading becomes unrealistically high. I have found no active scope probes so far, which would give a correct reading in a noisy environment. We hopefully should not see noise on the Vcc planes more than a few hundred mV. In contrast, many scope probes can pick up spikes as big as volts from the environment. If
Re: pulse modulation in reverb chambers
You were correct in your initial interpretation. I am wondering if a 1 us pulse can be established and not smeared over a longer period of time. The source antenna emits a coherent wave with this pulse modulation envelope, but many different rays taking different paths converge at the receive antenna at different arrival times. As long as those delays are much shorter than 1 us (path difference much less than 300 meters), the original modulation is received. But if delays are too long, then the pulse smears. What I was looking for was how to relate the smearing to room size. As Mr. DeWitt pointed out, the dependence is not on room size alone, but also on the Q of the room. Since I don't know how to analytically predict any of this, and I don't know the Q of the room, I was asking if the previously submitted check seemed reasonable. From: John Woodgate j...@jmwa.demon.co.uk Reply-To: John Woodgate j...@jmwa.demon.co.uk Date: Sun, 27 Jul 2003 18:52:33 +0100 To: emc-p...@majordomo.ieee.org Subject: Re: pulse modulation in reverb chambers I read in !emc-pstc that Ken Javor ken.ja...@emccompliance.com wrote (in bb49768d.3717%ken.ja...@emccompliance.com) about 'pulse modulation in reverb chambers' on Sun, 27 Jul 2003: So if I am worried whether the 1 us pulse width can be sustained, and I don't know how to determine it analytically, my plan is as follows: I put a wire probe in the room, run it to a spectrum analyzer tuned to the transmit frequency, put the analyzer in zero span mode with a 1 or 3 MHz bandwidth and look at the modulation waveform. If it is significantly longer than 1 us, I know my constructive interference path delays are smearing the modulation away. I originally thought you wanted to establish a reverberant field with a 1 us pulse. Now I'm not so sure. By 'modulation', you mean the envelope of the 1 us pulse? Isn't the idea of a reverberation chamber that once it is excited the energy takes a long time to die away? That means that the original pulse will be s t r e t c h e d, dying away exponentially if the room is a good one. A too-short pule would almost certainly produce a delay that was not exponential. You can only 'sustain' the 1 us pulse if your receiver is in the 'direct field' of the antenna, i.e. the field strength due to the direct propagation path from sending antenna to receiving antenna is at least 3 dB above the combined field strength due to all indirect paths. You can easily see this if you consider just a few simple specular reflections, which appear at the receiver as a series of overlapping (since their path lengths are less than 300 m) 1 us pulses of varying level. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: pulse modulation in reverb chambers
I read in !emc-pstc that Ken Javor ken.ja...@emccompliance.com wrote (in bb49768d.3717%ken.ja...@emccompliance.com) about 'pulse modulation in reverb chambers' on Sun, 27 Jul 2003: So if I am worried whether the 1 us pulse width can be sustained, and I don't know how to determine it analytically, my plan is as follows: I put a wire probe in the room, run it to a spectrum analyzer tuned to the transmit frequency, put the analyzer in zero span mode with a 1 or 3 MHz bandwidth and look at the modulation waveform. If it is significantly longer than 1 us, I know my constructive interference path delays are smearing the modulation away. I originally thought you wanted to establish a reverberant field with a 1 us pulse. Now I'm not so sure. By 'modulation', you mean the envelope of the 1 us pulse? Isn't the idea of a reverberation chamber that once it is excited the energy takes a long time to die away? That means that the original pulse will be s t r e t c h e d, dying away exponentially if the room is a good one. A too-short pule would almost certainly produce a delay that was not exponential. You can only 'sustain' the 1 us pulse if your receiver is in the 'direct field' of the antenna, i.e. the field strength due to the direct propagation path from sending antenna to receiving antenna is at least 3 dB above the combined field strength due to all indirect paths. You can easily see this if you consider just a few simple specular reflections, which appear at the receiver as a series of overlapping (since their path lengths are less than 300 m) 1 us pulses of varying level. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: self blinking LEDs as EMI sources WAS: LED lamps
Interesting observation. You said hum gets louder. Implying hum is already there. What kind of phone? Is it only that one telephone instrument? Only occurs when LEDs are near the instrument, not near the phone lines with the phone in another location? Is the effect more pronounced at less than 3m? Are the LEDs turned on/off while appear to be on? In other words, LEDs are OFF then come ON OFF ON OFF ON OFF at some high rate, perhaps near the 50Hz frequency? Do the LED ckts affect an AM/FM radio held close by? - Robert - Robert A. Macy, PE .. m...@california.com 408 286 3985 . . . .. . . fx 408 297 9121 AJM International Electronics Consultants 101 E San Fernando, Suite 402 San Jose, CA 95112 On Sat, 26 Jul 2003 11:36:37 +0800 Wan Juang Foo f...@np.edu.sg wrote: Dear All, I observe recently that some self blinking (and color changing) LEDs 'are' what seem to be a substantial emitters of radiated emission/interference. These LEDs are rigged up by hobbyists as decorative illuminators and acts more or less like the blinking lights for Christmas trees. I observe that each of theses circuits can be made to hung like Christmas tree ornaments. I came across a situation where the telephone lines were 'substantially noisier' :-) when several sets of battery operated circuits was about 3 m away from the telephone. It is not a very scientific method but I did a quick check and found by the method of elimination ;-) or what some would call systematic trials to find the source of the problem. It took me by surprise that the LEDs had a substantial role to play in the interference. LED circuits gets connected (on), hum gets louder. LEDs circuits gets disconnected, hums gets quieter and so on and so forth... These are very simple circuits with a single resistor and the LED in series. The 2 AA sized NiCad battery with holder, single resistor and LED including wire, total length about 5, tip to tip. These circuits were found to (well at any rate, seems to) emit interference that cause a telephone to pick up (50Hz) hum! It looks like the mains hum was pick up and modulated by the 'device' and reradiated or broadcasted... I can see that the blinking action at about 1 Hz have a duty cycle and that may generate a lot of ringing but what is surprising is the interference finding its way into the a telephone handset! I find it hard to believe that how the 'carrier' of the mains hum can eventually gets demodulated a puzzle. One wonders what can be observed if I get the circuits to a OATS? There again, how do I recreate the 50 Hz environment to couple the mains into these LED circuit? I had the Helmholtz coil in mind but can that be 'treated' as part of a test setup? Did anyone here have similar observation? One wonders if there any 'product specific standards' for such battery operated device that uses LEDs as decorative illuminators. :-) One wonders what will happen if there are such gadgets line up to 'hit' the market this Christmas... Looks like there will be a lot of testing work coming for EMC engineers! Tim Foo --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
