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RE: [802.3ae_Serial] 12 dB return loss for transmitter?

Tom
 
This is the return loss looking back into the transmitter.  Typically it is measured with the
drive circuit powered.  It is an AC measurement, and may vary according to the signal that
the transmitter is sending out.
 
The value of this measurement is in calculating or simulating the third pass signal, which is the
combination of the driving signal together with the reflection from the destination, coming back to the
source and reflecting again.  The total reflection from the source termination and the load termination
should be at least 20 db total for +/-10 percent ripple in the rails of the eye pattern.  So, 12 db at
each end would be 24 db or about +/ -6 percent ripple.  So, you normally want to do better.  20 db is
a very safe number at both ends resulting in 40 db or only about +/-1% ripple in the rails.
 
Ron miller
-----Original Message-----
From: Lindsay, Tom [mailto:tlindsay@stratoslightwave.com]
Sent: Tuesday, February 05, 2002 9:24 PM
To: Serial reflector 802.3ae (E-mail)
Subject: [802.3ae_Serial] 12 dB return loss for transmitter?

Dave Kabal, Dubravko and I were discussing the 12 dB return loss spec in Table 52-12.
 
What is it? Is this return loss looking back into the transmitter port from outside, or is it tolerance to return loss of the cable plant and receiver combination?
 
If the former, what is the technical reasoning? If the latter, it should at least be renamed or more preferably removed.

Thanks, Tom
Stratos NW
425/672-8035 x105