Power over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling. The IEEE standard for PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable if less power is required. Power is supplied in common mode over two or more of the differential pairs of wires found in the Ethernet cables and comes from a power supply within a PoE-enabled networking device such as an Ethernet switch or can be injected into a cable run with a midspan power supply.
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This is not meant to be a text book on transmission but is intended to remove some of the mystery associated with various methods of transmission. Many approximations and simplifications have been used in writing this guide. This is to make the subject more understandable to those people not familiar with the theories. For general application in the design of CCTV systems it should be more than adequate and at least point the way to the main questions that must be addressed. The manufacturers of transmission equipment will usually be only too keen to help in final design.
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Cable Transmission Cable Types
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For the purposes of this article the following conventions have been used. Fibre Optics is the technology of transmitting data along cables that consist of Optical Fibres.
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By using unshielded twisted pair transmission, CCTV system designers can offer their customers more bang for their buck. By Guy Apple From: http://www.foresight-cctv.com/sptnews.htm
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