As Mr. Macy said in an earlier email, this floating plane solution works best when the ribbon cable is driven in a perfectly balanced manner. Any imbalance in the signal current of the ribbon may drive the floating plane into a dipole antenna (depending on the size and shape of the plane) as I described in an earlier email.
George From: [email protected] [mailto:[email protected]]On Behalf Of Ken Javor Sent: Friday, September 16, 2005 4:33 PM To: [email protected] Subject: Re: When is a cable shield not a cable shield? If we grant that an image plane can reduce radiated emissions when placed adjacent to PCB, it seems it would also follow that an image plane next to a ribbon cable could perform likewise. However, if that were the intent, it would seem cheaper and more effective to include the image plane as a foil layer built into the ribbon cable assembly. If a manufacturer has gone to the trouble and expense of weaving a braided shield around the ribbon cable, then the only way to get the maximum achievable performance from that shield is to peripherally terminate it at both ends. > From: "Adam Bullivant" <[email protected]> > Date: Fri, 16 Sep 2005 14:59:56 +0800 > To: <[email protected]> > Subject: RE: When is a cable shield not a cable shield? > > Hi Group. I'm a first time poster. > > An interesting discussion! I remember doing some research 10 years ago in a > previous employment looking at the radiated emissions from pre-fabricated > Printed Circuit Boards with and without (floating) groundplanes. Dimensions of > the board were around 15cm by 10cm with simple trace configurations (go and > return) to a battery. The (common mode CM) radiated emissions between 30MHz > and 1GHz were greatly reduced with the floating groundplane in place. This is > due to the image of the CM current in antiphase causing the far field > cancellation. I assume a similar principle would apply to ribbon cable with a > floating shield assuming good coverage? This point does not consider low > frequency magnetic field. > > Regards > > Adam Bullivant. > > > > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of John > Woodgate > Sent: 16 September 2005 14:10 > To: [email protected] > Subject: Re: When is a cable shield not a cable shield? > > > Ken Javor <[email protected]> wrote (in > <bf4f5626.2c1f5%[email protected]>) about 'When is a cable > shield not a cable shield?', on Thu, 15 Sep 2005: > >> The reason for terminating the shield at both ends at high frequencies >> (cable electrically long) is to contain the eddy currents on the >> interior of the equipment enclosure, of which the shield is an >> extension, just as a tunnel or skyway between two buildings becomes an >> extension of the buildings it connects. > > It's better to keep the eddy currents to the OUTSIDE of the enclosure, > because if they flow on the inside, they can radiate into internal > circuits. This can be achieved by using metal-shelled free connectors > with 306 degree contact with both the cable shield and the shell of the > mating fixed connector which is attached to the outer (conducting) > surface of the enclosure. > -- > Regards, John Woodgate, OOO - Own Opinions Only. > Deadlines are 90% of deadliness. > http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk > > - > 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 > > - > 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 > - 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 - 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
