![]() If you only add the EMI at each grey dot (the top and bottom of each twist), both wires end up receiving +22v of interference.Įven though the final voltage received on the right side of the wire is different, notice that the difference in voltage is consistent throughout the twisted pair of wires: it is always 100v apart. The source of the EMI is the red circle, and each wave that surrounds the EMI source impacts the wires progressively less and less. The blue wire starts with +50v, and the green wire starts with the exact inverse, -50v. Allowing the receiving end to extract the intended signal from the EMI. If two wires, who are sending the opposite voltage on a wire, "take turns" being closest to the source, they will both be exposed to the same amount of inbound EMI. The strategy revolves around the fact that the EMI interference will be greater the closer a wire is to the source. To offset this, another strategy was devised to reduce the absorbed EMI on a Balanced Pair. Why does UTP twist the wires around each other?ĭespite the strategy above of using a Balanced Pair, there is no avoiding the fact that any electrical wire will be exposed to some amount of inbound EMI. ![]() So far we’ve only answered why we use a pair of wires, we will look into why they are twisted next. This allows you to use wiring schemes that don’t require heavy investments in shielding, and is a part of the reason for the prolific use of Unshielded Twisted Pair (UTP) cabling instead of Shielded Twisted Pair (STP) This is referred to in the electrical engineering world as a Balanced Pair, and is represented in twisted-pair wiring with the TX+ and TX- wire. (It isn't a perfect net 0 emission, but you can see the concept). The combined effect of leaking +0.5v and -0.5v ends up being outbound emission of 0v. To offset this, use another wire to transfer the exact opposite: -5v, which will have the effect of also leaking -0.5v to neighboring cables. Presume transferring +5v leaks +0.5v to neighboring cables. The solution devised is to transmit two signals inverse from each other.įor example, presume we need to send a voltage of +5v from one end of a cable to the other. But often cables are run alongside many other cables, and the idea of one cable's outbound EMI affecting the transmissions of other wires next to it is undesirable. If there is only one cable in use, then that isn't much of a problem. Voltage applied to a wire emits outbound EMI. The first mainly reduces outbound EMI, the second reduces inbound EMI. Why does UTP twist the wires around each other?īoth questions have to do with Electromagnetic Interference (EMI). ![]() Your question revolves around two other, but related questions: Zac67 did a great job of answering it, but I'd like to give my own take on it. As Criggie has pointed out, using a modular transceiver (SFP) with a decent switch is preferable to an external media converter.
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