Because one of the assumptions is lots of CM noise on the pair. The pair could be DC to a temperature sensor and have so much common mode noise as to be a problem.
There is lots of CM noise to deal with in this example. Although this does not necessarily have anything to do with a DC driven temperature sensor, that example is a significant hint., Doug University of Oxford, Course Tutor Department for Continuing Education Oxford, Oxfordshire, United Kingdom -------------------------------------------------- Doug Smith P.O. Box 60941 Boulder City, NV 89006-0941 TEL/FAX: 702-570-6108/570-6013 Mobile: 408-858-4528 Email: d...@dsmith.org Web: http://www.dsmith.org -------------------------------------------------- On Mon, 5 Feb 2018 09:48:13 -0800, "Orin Laney" wrote: If it's a balanced feed, why bother with a shield at all? -----Original Message----- From: si-list-bou...@freelists.org [mailto:si-list-bou...@freelists.org] On Behalf Of Lee Ritchey Sent: Monday, February 05, 2018 8:58 AM To: cor...@sonic.net; d...@emcesd.com Cc: emc-p...@ieee.org; si-l...@freelists.org; si-list-bou...@freelists.org Subject: [SI-LIST] Re: shielded cable connections Connect the shields to what? If the cable goes to an antenna, no connection is needed. -----Original Message----- From: si-list-bou...@freelists.org [mailto:si-list-bou...@freelists.org] On Behalf Of Chuck Corley Sent: Saturday, February 3, 2018 8:28 PM To: d...@emcesd.com Cc: emc-p...@ieee.org; si-l...@freelists.org; si-list-bou...@freelists.org Subject: [SI-LIST] Re: shielded cable connections >A few years later another experiment brought the FCC to my house, but >that is another story. OK I'm hooked. Someday (after you reveal your current mystery) you'll have to tell that FCC story. Chuck Corley National Instruments On 2018-02-03 20:06, Doug Smith wrote: > 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 > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-requ...@freelists.org with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > http://www.freelists.org/webpage/si-list > > For help: > si-list-requ...@freelists.org with 'help' in the Subject field > > List forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > http://www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-requ...@freelists.org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-requ...@freelists.org with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: http://www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-requ...@freelists.org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-requ...@freelists.org with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: http://www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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