Hi All, I have another riddle for you, this time a video is not needed. We all know that cable shields need to be connected on both ends to work at high frequencies, but do they? Imagine the case of a source in a metal box driving a shielded cable, let's assume it is shielded twisted pair and we are worried about the common mode noise on the pair radiating or ESD noise getting in and saturating the receiver in the box, exceeding its common mode range. We can also assume that the shielded connector on the first metal box is ra eally good one with a 360 degree connection to the box. The other end of the shielded cable goes to another metal box with a passive circuit inside, say a temperature sensor connected to the twisted pair wires. There is one special, but not uncommon, case where it does not matter if the shield is connected to the second box or not (or even if there is a second box at all), it will work in either case! Do you know what that case is? This is another experiment I do during my classes. I prove the conditions needed for the situation above and what the limits are. I am pretty much a lab rat and I have devised experiments to test the limits of most all EE concepts I have learned. I find there is more than meets the eye on most every principle. I started doing experiments like this around age 11 when I duplicated one of Marconi's experiments to see if it really worked, it did, although I suspect the neighbors may have had a rough time watching TV that day in 1958. A few years later another experiment brought the FCC to my house, but that is another story. Doug - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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: Jim Bacher: <[email protected]> David Heald: <[email protected]>
