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Chapter 2. Twisted Pair > Radio Frequency Interference

2.4. Radio Frequency Interference

Twisted pair cable and other in-house wiring are used to carry signals from one end, within an office or a home, to another end. Part of the signal energy is lost during transmission; becoming heat and electromagnetic radio waves. At high frequencies, the signal loss is relatively heavy, and the amount of radiation could become quite significant to the degree that it could affect other sensitive radio transmission systems occupying the same frequency band. The radio interference caused by twisted pair cable or in-house wiring can be considered as an extension of the crosstalk effect. Crosstalk is an electromagnetic phenomenon between two pairs of cables laid next to each other. The same electromagnetic wave that causes crosstalk also propagates through open space. The fact that there is no electromagnetic shield on a twisted pair cable or on most in-house wirings makes the radio propagation worse.

In traditional terms, the pair causing the crosstalk is called the disturbing pair, and the radio emission from a cable is called the egress. Therefore, the egress from a twisted pair or an in-house wiring is from the disturbing pair. On the other hand, the same electromagnetic mechanism causes a twisted pair cable or in-house wiring to pick up noises from an interference field from other radio transmission systems. Again, in traditional terms, the pair receiving the crosstalk is called the disturbed pair, and the radio emission to a cable is called the ingress. Therefore, the ingress to a twisted pair or in-house wiring is picked up by the disturbed pair. In practice, a twisted pair cable or in-house wiring is used to transmit and receive signals acting as both a disturbing and disturbed pair simultaneously. A twisted pair cable or an in-house wiring needs to deal with both egress and ingress issues.


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