Why Are Twisted-Pair Cables Needed and How Do They Work?
There are some mysteries in life, and one that’s always puzzled me is why twisted-pair cables can reliably transport information over much longer distances than a neat and straight serial or parallel cable where all the just go from pin to pin without any twisting. Anyone dealing with USB, RS232, RS485 and RS422 cables and converters likely has come across that syndrome, and most tend to simply accept it as another one of those physics things that you need a degree in electrical engineering to understand. But since it is nice to know how and why things work, let’s take a look what limits the length of straight-through cables and what enables twisted pairs to do better. Let’s start by asking ourselves what a cable needs to do. That’s simple: it needs to reliably let the other end know whether it has just transmitted a logical “zero” or a logical “one,” also known as “space” and “mark.” In RS-232 that’s accomplished by sending either a positive or a negative voltage relative to a common
