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Twisted Pair

Reducing Electromagnetic Interference In Everyday Communications

Steve Smith talks about the invention of the Twisted Pair, invented by Alexander Graham Bell, and how it made it possible for interference free communicating.

Episode #3-31 released on April 28, 2013

The twisted pair was a very important invention, that is stilled used to this day. The twisted pair cables where invented by Alexander Graham Bell, in 1881. The particular usage scenario of the twisted pair, is to reduce the amount of electromagnetic interference, referenced to as noise.

During that time period, the electromagnetic interference was being created by the cables of the electric Trams being installed in many cities, that happened to be close enough to the telegraph lines to cause issues with communications.

An attempt to use balanced pairs was initially used detect the differences between the two cables, and this method is known as a differential mode transmission. The coupling of electric or magnetic fields tended to couple to both wires equally, reducing or canceling the noise received by the receiver. Since this method does refer of the distance of the interference being away from the signal cable, if any interference is received by the signal wire, the common-mode rejection protocol of the receivers may not be able to screen the transmission for interference. This could induce a crosstalk with other cables along the entire length of the cable, making communications nearly impossible. Much like a feedback loop in a microphone-speaker setup.

Alexander Graham Bell, invented a way, called the twisted pair, that allows for both cables carrying opposite signals to be close enough together to receive equally the interference, and allow for cleaner communications by calculating the differences between the two signals that are equally subjected to the signal, and therefore retain the essence of the signal. The entirety of the United States was wired with the twisted pair along the whole of the telephone network.

The twisted pair can still be affected by electromagnetic interference when several twisted pairs are close together. To combat this, twisted pairs that are grouped together normally have a different pitch, or twisting rate. This significantly reduces cross talk, as a result.

You have several types of twisted pairs. There is the FTP, or foiled twisted pair, which uses foil to insulate the twisted pair from electromagnetic interference. There is the shielded twisted pair, which is capable of preventing the exiting or entering of electromagnetic interference, and reduces the likely of cable crosstalk. Then there is the UTP, or unshielded twisted pair, which has no external shielding. This kind of cable is used in many applications such as telephone wiring in homes and offices. Network cables, also, implement this, especially as patch cables, and this due to the flexibility of the cables themselves.

Know another invention created by Alexander Graham Bell? The telephone, was successfully created and tested in March 10, of 1876.

Next week, I'll be looking into the new Ubuntu 13.04, code named Raring Ringtail, and showing you around the nearly updated operating system, as well as providing some useful tips.

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Host : Steve Smith | Music : Jonny Lee Hart | Editor : Steve Smith | Producer : Zed Axis Productions

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