JS it is the return path impedance at signal frequencies that affects the performance. Ground the cable or hook it to an arbitrary DC voltage that is bypassed and the shield will provide a return path independent of cable length. Leave the shield open, and how it affects the signals will be frequency and length dependent. Essentially, an open shield forms a tuned resonator with the inner conductors. Steve. On 8/2/2013 4:26 PM, JS wrote: > Thanks Steve. Capacitance-to-ground (shield) unbalance is major cause > of IPS. Is this because common mode currents require a ground > connection? The pair's shield is present in both cases, just in one > cases it is grounded. So if we measure the pair with shield > ungrounded, we just measuring mutual capacitance unbalance (instead of > it and cap-to-ground unbalance)? Anyone with a thorough explanation > much appreciated! Many thanks! > > > ------------------------------------------------------------------------ > *From:* steve weir <weirsi@xxxxxxxxxx> > *To:* si-list@xxxxxxxxxxxxx > *Sent:* Thursday, August 1, 2013 10:57 PM > *Subject:* [SI-LIST] Re: Why is shield grounding necessary for Inpair > Skew (Intra pair skew)? > > In two words: unequal capacitance. > > Steve. > On 8/1/2013 6:25 PM, Jus wrote: > > Hi, I am interested in in-pair skew. Hoping another expert could > help! :) Does anyone know why grounding a differential pair shield > (ex. twinaxial or twisted pair foil) is needed to generate high > within-pair-skew (intra-pair skew)? For instance, with the pair's > shield grounded the in-pair skew value may be 10 ps/ft, while it is > only 2 ps/ft with shield ungrounded (shield left floating). Why does > grounding the shield dramatically increase In-Pair Skew? Are there any > cases where a differential pair's overall shield or individual shield > should be left ungrounded when measuring in-pair skew? I think I know > the answer, hoping for confirmation. Any assistance much appreciated!:) > > > > Jus > > > > > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx <mailto:si-list-request@xxxxxxxxxxxxx> > with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx <mailto:si-list-request@xxxxxxxxxxxxx> > with 'help' in the Subject field > > > > > > List forum is accessible at: > > http://tech.groups.yahoo.com/group/si-list > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > > -- > Steve Weir > IPBLOX, LLC > 1580 Grand Point Way > MS 34689 > Reno, NV 89523-9998 > www.ipblox.com > > (775) 299-4236 Business > (866) 675-4630 Toll-free > (707) 780-1951 Fax > > All contents Copyright (c)2013 IPBLOX, LLC. All Rights Reserved. > This e-mail may contain confidential material. > If you are not the intended recipient, please destroy all records > and notify the sender. > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx <mailto:si-list-request@xxxxxxxxxxxxx> > with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx <mailto:si-list-request@xxxxxxxxxxxxx> > with 'help' in the Subject field > > > List forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > > -- Steve Weir IPBLOX, LLC 1580 Grand Point Way MS 34689 Reno, NV 89523-9998 www.ipblox.com (775) 299-4236 Business (866) 675-4630 Toll-free (707) 780-1951 Fax All contents Copyright (c)2013 IPBLOX, LLC. All Rights Reserved. This e-mail may contain confidential material. If you are not the intended recipient, please destroy all records and notify the sender. ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu