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802.3bt

3 comments on “Double Power with IEEE 802.3bt Power over Ethernet

    • It’s not, it only uses the two pair. They’re just saying the CAT5/6 specifications have 4 total pair. Data only uses 2 pair (1+3, 2+6) .

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    • It is much worse ;-). Not only power uses all 4 pairs, but the data are transferred on all those pairs, and what is the worst, in both directions (transmit/receive) in the same time. How is it possible?
      First, power and data on the same pairs utilizes maybe hundred years old idea of phantom circuit, see Figure 2,
      Second, data transfer on one pair in both direction uses basic principle of tension superposition. Let say that binary zero is represented by -5 V and binary one by +5 V. If I send to the pair +5 V and party -5 V, result is 0 V. So if I measure tension in pair (0 V) and subtract my value +5 V from it, I get party contribution (-5 V).

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