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IMO, for the test to be useful it is critical that the test conditions be well controlled. The currently specified ferrite clamps are not really well specified.
Moreover, the exact layout and condition of the rest of the cable, from the ferrites to the link-partner have also not been well defined in the past. I suggest that the exact arrangement and the condition be better defined. E.g. exact and shorter distance between the DUT and the clamp. Minimum 10 pieces of
ferrite clamps with certain properties (size, material, TBD). The entire cable should be at 5cm over metal plane without coiling any section of the cable. Serpentines are allowed, with minimum of X cm (TBD) space between the segments. I also suggest shortening
the length of the specified cable, otherwise it is not going to be practical. Only if these parameters have been well defined would the method be potentially useful. I see this is moving by inertia, and I think the CM Clamp will be adopted here again, although there is a better and more relevant clamp available and used
in the regular EMC setups, and is more suitable in my strong opinion. It is EM Clamp. N From: Cibula, Peter R [mailto:peter.r.cibula@xxxxxxxxx]
Dear Colleagues and Rx CMNR ad hoc participants, Thanks very much for your participation in yesterday’s ad hoc meeting. Two follow-up items from the discussion: #1 –Thanks to Dave Chalupsky for posting yesterday’s
contribution from Bryan Moffitt (Examination of 802.3-2012 Annex 40B Cable Clamp), now available at the P802.3bq public area. #2 – Proposed text for Clause 113.5.4.3 from that contribution is repeated here for your consideration. 113.5.4.3 Rejection of External EM Fields
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When the cabling system is subjected to electromagnetic fields, currents are generated in the shield which may be converted to interference. This specification
is provided to limit the sensitivity of the PMA receiver to external EM fields picked up by the cabling system. It provides an assessment method of the electromagnetic performance of the link segment and the PHY, including the MDI.
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A test can be made using the cable clamp test defined in 40.6.1.3.3. A 6 dBm sine wave source from 80 MHz to 2000 MHz can be used to generate an external electromagnetic
field and corresponding shield current.
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A system integrating a 40GBASE-T PHY may perform this test. Operational requirements of the transceiver during the test are determined by the manufacturer. Please review this text and feel free to use the reflector for further discussion. Best regards, P802.3bq Rx CMNR ad hoc Chair |