The following is my opinion, I haven't performed such an experiment. I don't think the quasi-peak detector is really an issue with regards to how many simultaneous pings are sent. The quasi-peak detector will give the same response (dB relative to peak detection) regardless of how many pings are sent simultaneously. If the pings are sent asynchronously, the quasi-peak detector could come into play if the pings are sent often enough and time delayed just right such that the quasi-peak detector sees a net increase in signal over its sample time. Of course the signal received at any point in time is now 1/4 what is was when we had synchronicity. But the signal would read higher than if the pinging were random and at a low rate relative to the quasi-peak detector sample time. It would seem to me that unless the four cables were part of a quadruply redundant bus, that synchronizing or setting precise time delays is an overly pessimistic model of the real world.
---------- >From: George Stults <[email protected]> >To: "'[email protected]'" <[email protected]> >Subject: coherent noise >Date: Thu, May 2, 2002, 4:22 PM > > > Hello Group, > > I'm considering the following problem having to do with effect of coherent > (or synchronized) noise versus non-coherent (or asynchronous) noise on a > device with several I/O cables. > The EUT would be described as follows: A computer with 4 Ethernet ports. > For this example I'll PING the lines as a method of putting traffic on them. > [AFIK the standard calls for pseudorandom traffic whereas PING is fairly > periodic, but this is easier to describe for now]. Anyway, I can > provide the PING traffic in one of two ways. > [NOTE - PING refers to a program that repetitively sends an address query > out the Ethernet port and reports whether it got a reply] > Method one is to connect all 4 Ethernet Ports to a single HUB and plug in a > second computer to same HUB to send a PING to the EUT. That way the same > signal is traveling down 4 lines at the same time, more or less in phase > [depending the details of the HUB construction]. > The second method is to use one computer per port (4 external computers) to > each run the PING program separately. In this case the PING traffic is > asynchronous because each source is separate. > I know from experience that the second method is quieter from the standpoint > of radiated emissions using quasi peak detection. I assume that the main > reason is that quasi-peak averages them down since they're not in phase. > And vice versa. > All the above is to describe a typical example of the problem. > What I'm looking for is a method to quantify or predict the gain or loss in > terms of quasi peak detection for an EUT with synchronized versus > asynchronous signals over multiple I/O cables. > Any thoughts appreciated - thanks in advance > George Stults > > > ------------------------------------------- > 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > ------------------------------------------- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
