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*To*: STDS-802-3-10SPE@xxxxxxxxxxxxxxxxx*Subject*: [802.3_10SPE] Multidrop MDI return loss edit homework comment 425*From*: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>*Date*: Tue, 22 May 2018 02:02:17 +0000*Accept-language*: en-US*Delivered-to*: mhonarc@xxxxxxxxxxxxxxxx*List-help*: <https://listserv.ieee.org/cgi-bin/wa?LIST=STDS-802-3-10SPE>, <mailto:LISTSERV@LISTSERV.IEEE.ORG?body=INFO%20STDS-802-3-10SPE>*List-owner*: <mailto:STDS-802-3-10SPE-request@LISTSERV.IEEE.ORG>*List-subscribe*: <mailto:STDS-802-3-10SPE-subscribe-request@LISTSERV.IEEE.ORG>*List-unsubscribe*: <mailto:STDS-802-3-10SPE-unsubscribe-request@LISTSERV.IEEE.ORG>*Reply-to*: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>*Spamdiagnosticmetadata*: NSPM*Spamdiagnosticoutput*: 1:99*Thread-index*: AdPxb1iB1BRb1GYKT8WWtT9Hq6VWWA==*Thread-topic*: Multidrop MDI return loss edit homework comment 425

After discussing with Piergiorgio and David Brandt, and looking at other BASE-T clauses, we determined that a figure was not necessary, but the reference impedance needed to be specified as a the two 100 ohm
end terminations in parallel. The result is the following proposed response: Here is the new proposed response: Change “In multidrop configuration the MDI shall be terminated by two 100 (nominal) impedances satisfying Equation (147–6) when measured with 100 ±1% impedance at the edges.” To “In multidrop configuration, the differential impedance at the MDI for each transmit/receive channel shall be such that any reflection due to differential signals incident upon
the MDI from a balanced cabling terminated at both ends by 100 CAP OMEGA, and having a nominal differential characteristic impedance of 100 CAP_OMEGA, is attenuated, relative to the incident signal as per the relationship shown in Equation (147–6): “ (where CAP_OMEGA is capital omega) For reference, here is the comment and the original proposed response:
MDI return loss specifies the termination. Requiring the termination of the MDI would specify an implementation.
Change "In multidrop configuration the MDI shall be terminated by two 100 ? (nominal) impedances satisfying Equation (147-6) when measured with 100 ? ±1% impedance at the edges." to "The MDI return loss (RL) shall meet or exceed Equation (147-6) for all frequencies specified (with 100 ? ± 0.1 % reference impedance) at all times when the PHY is transmitting data." PROPOSED ACCEPT IN PRINCIPLE. Change "In multidrop configuration the MDI shall be terminated by two 100 ? (nominal) impedances satisfying Equation (147-6) when measured with 100 CAP_OMEGA ±1% impedance at the edges." to "The MDI return loss (RL) shall meet or exceed Equation (147- 6) for all frequencies specified (with 100 CAP_OMEGA ± 0.1 % reference impedance) at all times when the PHY is transmitting data." Notes: - CAP_OMEGA is capital omega - spaces before CAP_OMEGA and ± are non-breaking George A. Zimmerman, Ph.D. President & Principal Consultant CME Consulting, Inc.
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