John, Many thanks for helping getting a reply form the source. I mostly appreciate it. Neven
-------------- Original message -------------- From: John Woodgate <j...@jmwa.demon.co.uk> > In message > <062220060603.17444.449A32C1000E06B8000044242207020853CECE020A900A02@comc > ast.net>, dated Thu, 22 Jun 2006, neve...@comcast.net writes > >AFAIK, there is no spec on imbalance of (each diff pair of) a port, and > >I will check it with my local IEEE Ethernet spec specialists. I don't > >know if there is a spec on the cable, but I will try to find it. I'd > >really like to see if the requirement from the standard has any basis > >in the actual real-world measurements. > > Specially for you, I asked my standards committee colleague Martin > Wright, who is Chairman of CISPR/I, and his reply is: > > It is quite correct that CISPR 22 is trying to emulate the performa! nce > of cabled installations. The effect of installations on LCL remains an > open question. > > At the time that this part of CISPR 22 was written, many attempts were > made to obtain data on LCL of installations from telecomms and ITE > installers but the relative performance of installations from an LCL > perspective was (and still is) seen as 'sensitive' data and was never > released to the standards bodies. > > The LCL values in CISPR 22 were based on a series of measurements made > by Telstra in Australia along with private inputs from some of the > telcos represented in the working group (NTT, BT, FT and Telia). This > data was circulated to both ITU and ETSI with a question 'Does the LCL > shown in these curves form a reasonable representation of the installed > LCL of the cabling base in your country' and this did elicit some > responses. The curves were then re! -aligne d with this information. > > From the perspective of the UK, I know that there was a major analysis > of the Telecomms network at this time which showed that very few lines > were worse than the LCL specified. This result implies that the radio > spectrum will receive better protection (in most cases) than these > values would suggest. This has the corollary that the emissions from > the system could potentially be higher than the limits allow with no > adverse affects. > > Against this background we also need to consider the wireline proposals > where the radio users are pushing for limits at least 20dB below the > CISPR limits in order to better protect the radio spectrum. It would be > very difficult to write a valid definition of wireline which did not > include Ethernet, 10base T etc. > > These two facts (maybe) imply that the CISPR limit is an OK compromise ?! &g t; > The current/voltage measurement in CISPR 22 comes from a completely > different approach where the interest is in the power emitted, wherever > it comes from, which also has much support in CISPR I. This only > consider LCL in the indirect way that some of the power emitted will > come from the LCL conversion. > > As a final point the issue of LCL specification is certainly not closed > in CISPR I. There is a current active liaison with cable and > installation groups (TC46X, ISO/IEC JTC 1 WG 25 and so on) to better > understand the LCL and installation issues. > > I hope this helps to give the background to the requirements but please > note that I am condensing nearly 15 years of development into this short > email so may well have missed something significant. > > Regards > > Martin Wright, Chairman CISPR I > > Contact details fo! r Marti n are at:http://tinyurl.com/loy3x > -- > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk > 2006 is YMMVI- Your mileage may vary immensely. > > John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > > - > ---------------------------------------------------------------- > 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 emc-p...@ieee.org > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas emcp...@ptcnh.net > Mike Cantwell mcantw...@ieee.org > > For policy questions, send mail to: > > Jim Bacher: j.bacher! @ieee.o rg > David Heald: emc-p...@daveheald.com > > All emc-pstc 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. 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