I've seen quite a few good replies to this thread with some fun EM analysis. I'd like to offer a practical viewpoint (I know, I'm usually the one that's throwing Math around...so I'll take the other viewpoint this time)
I have my suspicions that some items are sold as "shielded" just so that the manufacturer can say so. The problem is, they didn't really know shielding theory; so they didn't know enough to terminate the shield. Over the years, I have seen quite a few "shielded" items that aren't very well terminated or very well shielded. I'm not sure what the case is with this particular cable. Maybe it's the result of a cable manufacturing that doesn't understand shielding theory; or maybe it's meant for a special purpose other than shielding. The braid will offer some shielding even if it isn't terminated...much of this depends on the length/width ratio of the cable, the frequencies of interest and the type of signals on the cable (common mode, differential mode, balanced, unbalanced...) >From a practical standpoint, I would take a hard look at this cable. If you don't have an EMI problem with the cable; then I would try an unshielded version in order to save cost. If you do have an EMI problem with the cable; than I would either try to add filtering to the signals on the cable (and then see if you can remove the shielding)...or I would look into getting a cable with a shield that has proper termination. Just the opinions of an amateur professional :-) Chris Maxwell, Design Engineer | Compliance Engineer Email: [email protected], Desk Phone: 315-266-5128 Engineering Department Fax: 315-797-8024 NetTest (New York) Inc. 6 Rhoads Drive, Building 4, Utica, NY USA Web: www.nettest.com, Phone: 315-797-4449 NetTest, a Member of the Anritsu Group - 2005 IEEE Symposium on Product Safety Engineering 3-4 October Schaumburg, IL http://www.ieee-pses.org/symposium 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 [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [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://www.ieeecommunities.org/emc-pstc
