Jim,
I am not a test-house, so I don't have experience with various ISNs. However, I have done a considerable amount of work in common-mode voltage and current measurements, as well as investigating imbalance (i.e. mode conversion) in differential-signaling, especially in the hi-speed signaling including Ethernet arena. So maybe I can give a little advice here. I don't know what's wrong with your ISN, but for measuring conducted emission (either CM currents or CM voltages) on high-speed differential signal lines I would never use anything that has RJ45 or similar connectors on it. Just conversion in the connectors and the un-twists of the cable in the area around the connectors can considerably affect common-mode voltages and currents on the signal line, so the measurement results are uncertain. If the un-twists of the twisted pairs at the connector are bad, that can cause considerable crosstalk between the pairs as well. Whatever the test method, the level of balance on the differential pairs must be preserved and not affected, or the results can be anything. For that reason I strongly prefer the clamp method over ISN. Clamp preserves the integrity of the signal line, and ISN is not well-defined in that respect. Some EMC test houses seem not to be aware of that, and I believe that even the ISN manufacturers are not paying attention to it. If I had to use ISN, for whatever reason - maybe for ease and speed of measurement compared with the clamp-test, I'd cut-off the RJ45 receptacles (and maybe some associated segments in the box) from the ISN. I would also cut off the RJ45 plugs from the ends of the cables that connect to it, design a better transition (with better balance, less mode conversion and crosstalk) between the cable that connects the ISN to DUT and from ISN to AUX, and then I'd verify the balance on a 4-port network analyzer. Hard-wiring the ISN into the signal line might do it, keeping extreme care to preserve the balance on the diff pairs. No time or space to elaborate more, but that is essentially keeping the twists of each pair tight and together, and at the same time separating each pair from its neighbor. Regards, Neven -------------- Original message -------------- From: jim.hulb...@pb.com We have an ethernet port to which is connected a CAT5 cable. When this cable is routed through an ISN per EN 55022 for conducted emissions measurements, the port is unable to function. What experience have people had with ISNs in this application, or what experience do people have with the alternate test methods (current probe and/or voltage probe measurements)? We are trying to establish a test procedure that yields repeatable measurements and hopefully measurements that are correlatable to what other labs may measure. Thank you. Jim Hulbert, Principal Engineer GMSE/TSO/Compliance Engineering Pitney Bowes- ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.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...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.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...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
