I read this at
Why does it transmit on more than 1 pin? Shouldn't it just need pin 2?
Google for "noise on cat5 cables" or "cross-talk cat5"
snipped-for-privacy@gmail.com wrote in part:
Correct.
Signals go out on two pins because two conductors are required to move each balanced signal. These balanced signals are very ingenious and allow all sorts of noise to be cancelled out.
Balanced signalling allowed 100baseTX to run 100 MHz over
100m of wild country at a time when solo signals could only eke out 50 MHz over 10 cm of highly structured PCB.-- Robert
Look up differential pairs.
Did it ?
100 Mbps, OK. But 100 MHz ? :-)
ISTR that CAT5-CAT6 are 150MHz bandwidth. I've never looked at the specs, maybe that's at 3db down.
We get GHz ethernet with modulation magic that I never realy figured out, even with the ham radio license.
Gerard Bok wrote in part:
Actually, I think 100baseTX clock is 125 MHz, and the encoding brings that _down_ to 100 Mbps. Of course, the encoding also puts most of the RF energy around 30 MHz, but the data is still up in short shifts.
-- Robert
Well 0 pins are required, as 802.11 shows you.
It is possible to send a signal down one wire, but it can't be close to any other wires.
Note that the signal doesn't actually travel down the wire, but in the space between the wires. The wires just remind the signal which way to go. At low frequencies, where the wavelength is much greater than the length, you can almost get away with considering the signal as traveling in the wire, and use one for each signal, plus one ground. This gets much harder at higher frequencies.
-- glen
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