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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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The Twisted Pair and the Principle of Immunity
The basic principle behind the twisted pair and its various implementations is shown in Fig. 1.5. At the very top of the figure is an analog signal being transmitted from the microphone of a traditional telephone to the loudspeaker on the other side.
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NOTE We are ignoring another clever technique here for the time being, by which we combine, and then later separate, the loudspeaker signal from the microphone (transmitter) signal, over a single twisted pairthis involves an innovation called the “hybrid transformer.” It is discussed in more detail in Chap. 13.
In the cases that follow in Fig. 1.5 ...

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