Not quite. What I am saying is that the 125 MHz and harmonics that have been observed are noise generated by the 125 MHz PLL coupled (unfortunalte fact of life) into the front-end signal. Killing it completely from the spectrum of the data-signal, e.g. by low-pass filtering above 100 MHz (theoretically anywhere above 62.5 MHz), would not affect the data rate Neven
-------------- Original message -------------- From: "Stu Benner" <[email protected]> I suppose you are trying to say the same thing as me in another way. Indeed the interface does clock symbols at a 125 MHz rate for both 100 Mbps and 1 Gbps Ethernet. If I recall correctly, for Gigabit Ethernet, symbols are transmitted as 4-level PAM (2 bits per symbol) on 2 pairs to achieve the 4 x 125 MHz data rate (less overhead yields 1 Gbps throughput). For the 100 Mbps version, symbols are transmitted on 1 pair and are binary to achieve the 125 MHz data rate (less overhead yields 100 Mbps throughput).. Indeed, there are numerous factors than can affect emissions. Regards, Stu Benner www.emcwizard.com <http://www.emcwizard.com/> From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Friday, October 06, 2006 2:45 PM To: 'IEEE EMC Discussion Group' Subject: RE: Ethernet emissions It is not a "symbol rate". It is PLL in the Ethernet PHY that gets turned on as soon as you get a 100 or Gig link. So, when you connect the remote end, the 100 or Gig link comes up and you see it. The emission level, however, depends on many factors, mainly the PHY itself, the transformer, the PCB andsystem/enclosure design. Regards, Neven -------------- Original message -------------- From: "Stu Benner" <[email protected]> Derek, 125 MHz is the symbol rate of 100 Mb and 1 Gb Ethernet. Ensure that the shield of the cable, if used, is terminated properly at the chamber penetration, the UUT, and at the exercising equipment. If there is an increase in emissions when the shielded cable is installed, this could indeed indicate significant common mode signals are being coupled onto the outside of the shield of the cable. Regards, Stu Benner www.emcwizard.com <http://www.emcwizard.com/> From: [email protected] [mailto:[email protected]] On Behalf Of Derek Walton Sent: Wednesday, October 04, 2006 2:38 AM To: IEEE EMC Discussion Group Subject: Ethernet emissions HI All, I have a system on test that has a single very strong emission at about 125 MHz. Is this an Ethernet related frequency? It appears to jump 20 dB when the receive end, outside the chamber, is plugged in. Also, with unshielded cables it's not there. With shielded its about 30 dB up at the same frequency. Anyone have suggestions as to the source? Thanks, Derek Walton L F Research - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discus! ! sion li st. 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