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
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