Aug 17, 2011

Cat-5 Length and Signal Strength

Cat-5 is a classification of Unshielded Twisted Pair cable in a category series determined by the Electronic Industries Alliance. Each category has particular performance requirements. Signal strength is relevant in relation to cable length because signals deteriorate over distance. The rate at which the signal strength reduces dictates the recommended length of segment for Cat-5 Unshielded Twisted Pair cable.

Unshielded Twisted Pair

  • Cat-5 is a type of structured cable called Unshielded Twisted Pair (UTP). This cable type does not have a metal shield surrounding the cables within. The metal shield in a cable protects against environmental magnetic interference. UTP does not need this shield because of the magnetic effects created by twisting pairs of wires together. UTP is one of the cable types recommended by the Ethernet standards, which are the most widely implemented recommendations in the world for the physical properties of networks. The lack of shielding makes UTP cheaper than other cable types, and so it has become the most implemented form of network cable.


  • When current passes along a wire, it creates a magnetic field around that wire. Incoming magnetic interference merges with that magnetic field. The two wires in each pair represent the negative and positive paths of a complete circuit. Twisting the wires together brings their magnetic fields into contact. They cancel each other out, taking the merged environmental magnetic interference with them. This protection against interference enables the cable to carry a signal for a particular length before that signal becomes so distorted by interference it becomes unusable.


  • Data signals travel over cable as an electric charge. Over distance, this charge weakens. This is called attenuation. Cat-5 is widely used in Ethernet networks. Ethernet recommends that a cable segment should not be longer than 100 meters, or 328 feet, although many implementations will not push a cable length further than 50 meters.


  • An Unshielded Twisted Pair cable can be run farther than 100 meters. The total length over which some signal strength remains is about 1,000 feet, or about 300 meters. The specification of the cable type requires it to have a capability to carry the signal to that length before it disappears entirely. That means that at 1,000 feet, the signal strength has already reduced to something that is less than usable. Cat-5 achieves a 99.9 percent depreciation of the signal strength at a length of 1,000 feet.


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