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Twisted Pair – a type of transmission media

– In this type of wiring media from a single circuit, two conductors are taken and twisted together so that they can cancel out the EMI (electromagnetic interference) from each other as well as external sources.
– External sources of interference include crosstalk between the pair of neighboring conductors and electromagnetic radiation from the UTP (unshielded twisted pair) cables.
– Alexander Graham Bell is known for inventing the twisted pair cabling.
– The operation in which the two conductors are loaded with equal but opposite signals is called a balanced pair operation.
– The difference between the two is detected at the destination.
– This altogether is known as the differential mode transmission.
– Signals are introduced in to the wires by the noise sources by coupling the magnetic and the electric fields.
– These sources also tend to equally couple both the wires.
– This leads to production of a common mode signal which gets cancelled at the receiving end up on taking the difference signal.
– However, this method does not succeed when the source of noise is located close to the signal conductors i.e., the wires.
– This is so because the wire closer to the noise resource will have more tendency to couple with the resulting noise and this cannot be eliminated by the common mode rejection of the receiving end.
– This problem is more common with the television cables where the same cable pairs lie close to each other for a number of miles.
– Crosstalk can be induced by one pair in to another and this keeps on adding along the length of the wires.
– Twisting is one of the effective ways of overcoming this problem.

– This happens as the wire nearest to the source of noise is exchanged up on half twist.
– But this would work only if the noise source stays uniform throughout the distance.
– The electromagnetic radiation given out by the cable is also reduced with the help of the differential signaling.
– It also helps in cutting down the attenuation when the distance is big enough to be covered.
– The rate at which the wire is twisted is called the twist rate or the pitch and can be defined as the number of twists per meter of the wire.

There are three types of twisted pair cablings available namely shielded twisted pair cabling (STP), foiled twisted pair (FTP) and unshielded twisted pair (UTP) cabling.
– The last one is different from the first two in the sense that it does not have any shielding.
– It is the primary media used for the telephone lines as well as computer networking such as in temporary network connections or the patch cables since this type of cabling is highly flexible.
– In the case of indoor telephone applications, this cabling is made in to a group of 25 pairs as per the standards defined by the AT&T Corporation.
– These wires are made from copper and their insulation is created from some insulating material called the polyurethane.
– On the other hand, the outdoor cables may consist of 1000s of pairs and the cable is broken down in to small bundles.
– Here, each bundle consists of pairs with variable twist rates.
– These bundles are also twisted that results in the cable.
– It is possible for the pairs with same pitch to experience some crosstalk.
– The pairs within a large cable have to be selected carefully so that the crosstalk is kept as minimum as possible.
– The twisted pair cabling find its major use in the data networks where there are connections of short and medium lengths.
– This is so because the twisted pair cabling is less expensive when compared to the coaxial cable and the optical fiber.
– These days UTP is even finding use in the security cameras i.e., the video applications.
– The bandwidth of the UTP cables has been increased so as to match with the baseband of the TV signals.

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