Sanjib – Yes, radiated emissions also need to be contemplated. But the good news is that the IEEE Standards body anticipated the potential for radiated emissions and has taken corrective measures. First, recognize that, like in 1000Base-T, 10GBase-T signaling is differential in nature and transmitted on twisted pairs that cancel emissions to first order. Nevertheless, there is residual radiation and even some common mode components due to non-idealities. To cope with those, IEEE was careful to architect the output energy of a 10GBase-T transmitter to be more evenly distributed over the transmission band and, furthermore, in Clause 55.9.5, requires compliant equipment to meet FCC Part 15 or CISPR 22 (depending on geography) limitations for radiated emissions. Bottom line: it’s purpose built to live and work in a data center environment without causing problems.
Good point! I am not much concerned with only one cable. But I think, usually there would be many...isn't it? I thought it would be challenging to meet EMC norms as they would emit more when the cables are unshielded?
But again I saw many have passed the EMC tests. One such example could be found below:
Hi Ron, I got your points on crosstalk & EMC. Yes, that's how it could be done. Thanks a lot!
Regarding the EMC (or rather EMI?) I was more concerned with the "unshielded cable" emitting RF energy creating trouble for others. Any thoughts?
Sanjib – The Cat6A cables I have seen reduce alien crosstalk due to plastic ribs in their core which specially separate the twisted pairs. Since electromagnetic radiation intensity falls off as the square of the emission radius, it’s a very effective technique.
As for Electromagnetic interference, I would agree with you if it wasn’t for the recent advances in the DSP algorithms inside of the 10GBase-T transceivers which have been shown to provide immunity to very strong EMI events of up to 10V/m. Those DSP engines are able to place a notch filter at the interferer’s emission frequency and prevent it from causing havoc with the received data.
As I know, the "alien crosstalk" was one of the biggest challenges for using the Cat6 cable for Gbit Ethernet. What is the change that is made in the insulation to reduce the alien crosstalk?
In the second para in this article, it is mentioned about using "unshielded cable" for 10GbaseT. Again, I still see a major risk in using an unshielded cable for 10Gbit/sec due to EMC concerns.
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