For GBit Ethernet use CAT5 cables only, unshielded or shielded. Neven -------------- Original message --------------
> If one wants to test the maximum of possible emissions, > the network switch should be connected with cables of > resonating length (so 1/4 lambda) for each available RF > frequency on-board and be tested accordingly. > Emission testing (unless for large EUT) is all about cables -antennas- !!!! > Measuring without wires will obscure 99% of the emission > properties of your network switch. > > Most emission is due to common mode current created by ground voltages > that appear between connectors on different places. > > A quarter lambda of cable has the maximum emissions property. > This makes emission testing unpractically long to carry out, > (cut cut cut) and requires immense measuring set ups for low frequencies. > So "we" decided! some time ago to start measuring radiated > E-field emissions (for civil apps) at 30 MHz, and in the FAR field to > overcome the measurement problems with magnetic field > emissions, and to standardize the cable layout into a > measurement volume (latest CISPR16), allowing for a maximum > (small EUT) of 2 x 80 cm H/V at each side ( or one side) of the EUT. > > Now at the end of this part of cable a typical termination > is required for those cables that carry SIGNALS with frequencies > within the measurement range (in band). Why terminate ? > Well, a badly terminated cable will transform differential mode > current ( the signal current) into common mode current. > ( if you do not know the difference between DM and CM current, > take your study book NOW, or you will never understand EMC)!!! > And common mode current radiates. It makes no sense to > typically terminate a ! 600 OHM PSTN cable from the view point > of emission testing, a s it carries no RF signals. > > Network cabling is divided into several categories (CAT 3,4,5) > These categories do correspond to high frequency signal > integrity (read symmetry) of the wire pairs. > > Low category cables will -due to bad symmetry and impedance > fluctuations- transform a part of DM current into CM current. > The measurement quantity that goes with these is called LCL - value > (Longitudinal Conversion Loss). This will create radiation, > independent of the quality of the screen, or connection to the enclosure. > > Another topic that rises here is where to place a auxiliary equipment > that might me necessary to initiate and maintain any network traffic. > If the cable set up requires 80H/80V cm and a termination, the AE > needs to be placed on the ground plane of the measurement volume (if it > fits), and its radiation will thus be included in t! he measurement results. > So we need a way to "get out" of the test volume, preferably outside the > screened room without this cable part contributing to the emission profile. > > For this reason a "duct" or metal conduit is used to guide the cable outside > the room, and on the room's screen a high quality (and complex) filter is > required to filter off any CM current from outside. The duct starts at the > centre > of any rotating platform, and the cabling from the edge of the test volume > to the duct may be used for terminating the cabling using ferrites (this is > not yet in the standards, I know) > SO EUT inside, within measurement volume, and AE outside measurement volume > filtered on the room's screen. > On an OATS this is somewhat confused. I usually extend cabling to such an > amount that the AE is definitely "out of sight" behind the EUT , and do some > expe! riments with cable lay out left and/or right of EUT. > > I hope this has been of inspiration to you.... > Any comments or additions ???? Anyone ??? > > > Regards, > > Gert Gremmen > Approvals manager > ====================================================== > ce-test, qualified testing > Member of EMC committee CENELEC/IEC > > + Independent Consultancy Services > + Compliance Testing and Design for CE > + Improvement of product quality and reliability > + Testing services according to: > Electro magnetic Compatibility 89/336/EC > Electrical Safety 73/23/EC > Medical Devices 93/42/EC > Radio & Telecommunication Terminal equipment 99/5/EC > > Website: www.ce-test.nl > Phone : +31 10 415 24 26 > Fax : +31 10 415 49 53 > ====================================================== > > > FW>-----Original Message----- > FW>From: owner-emc-p! [email protected] [mailto:owner-emc- > FW>[email protected]] On Behalf Of [email protected] > FW>Sent: vrijdag 28 januari 2005 19:46 > FW>To: [email protected]; [email protected] > FW>Subject: RE: OATS testing of network switch > FW> > FW>Dave, > FW> > FW>If the cables are shielded and the shielded are intimately connected to > FW>the Network Switch shielded enclosure (you have a shielded enclosure, I > FW>assume?), AND the loads do not excite common mode current, then these > FW>cables will not radiate. No common mode current- no radiation. > FW> > FW> Dave > FW> > FW>-----Original Message----- > FW>From: [email protected] > FW>[mailto:[email protected]] On Behalf Of Garnier, David S > FW>(GE Healthcare) > FW>Sent: Friday, January 28, 20! 05 11:39 AM > FW>To: [email protected] > FW>Subjec t: OATS testing of network switch > FW> > FW>Hello, > FW> > FW>We don't do routine OATS evaluation of stand-alone ITE products > FW>(other than items integrated in to our products,) so pardon my > FW>ignorance or poorly thought out questions. > FW> > FW>I have a couple of 8 port gigabit network switches I would like to > FW>evaluate on the OATS. ANSI C63.4-2003 gives me some guidance > FW>in this area, such as "each I/O port being terminated in typical load > FW>of actual usage." > FW> > FW>What kind of a circuit would I used for IEEE 802.3AB load? I am > FW>thinking transformer (?) passive, but placed where??? Directly > FW>plugged into the 8 port switch or placed on the end of short (length?) > FW>Ethernet cable? If I use short cables, how do I not create 8 small > FW>horizontal antennas 1 meter high? Comm! ents? > FW> > FW>Regards, > FW> > FW>Dave Garnier > FW> > FW>---------------------------------------------------------------- > FW>This message is from the IEEE Product Safety Engineering Society > FW>emc-pstc discussion list. Website: http://www.ieee-pses.org/ > FW> > FW>To post a message to the list, send your e-mail to [email protected] > FW> > FW>Instructions: http://listserv.ieee.org/listserv/request/user-guide.html > FW> > FW>List rules: http://www.ieee-pses.org/listrules.html > FW> > FW>For help, send mail to the list administrators: > FW> > FW> Scott Douglas [email protected] > FW> Mike Cantwell [email protected] > FW> > FW>For policy questions, send mail to: > FW> > FW> Richard Nute: [email protected] > FW> Jim Bacher: j.bacher@iee! e.org > FW> > FW>All emc-pstc postings are archive d and searchable on the web at: > FW> > FW> http://www.ieeecommunities.org/emc-pstc > FW> > FW>---------------------------------------------------------------- > FW>This message is from the IEEE Product Safety Engineering Society > FW>emc-pstc discussion list. Website: http://www.ieee-pses.org/ > FW> > FW>To post a message to the list, send your e-mail to [email protected] > FW> > FW>Instructions: http://listserv.ieee.org/listserv/request/user-guide.html > FW> > FW>List rules: http://www.ieee-pses.org/listrules.html > FW> > FW>For help, send mail to the list administrators: > FW> > FW> Scott Douglas [email protected] > FW> Mike Cantwell [email protected] > FW> > FW>For policy questions, send mail to: > FW> > FW> Richard Nute: [email protected] > FW> Jim Bacher:! [email protected] > FW> > FW>All emc-pstc postings are archived and searchable on the web at: > FW> > FW> http://www.ieeecommunities.org/emc-pstc > > ---------------------------------------------------------------- > 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-pst! c postings are archived and searchable on the web at: > > ; http://www.ieeecommunities.org/emc-pstc ---------------------------------------------------------------- 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
