If we have some message or information signal to transmit over a distance without using a cable, electrical or optical fibre, then we need to use a radiofrequency signal to radiate the information. Suppose we have a digital message to send, i.e. a message which is just a sequence of binary digits, Os and Is. We could connect this signal to a piece of wire, and some of the signal would radiate into space as an electromagnetic wave. In principle, that electromagnetic wave would induce a voltage on a corresponding piece of wire some distance away and, after (much) amplification, a replica of the signal, contaminated by noise and other interference, could be recovered.
Modulation and modems, Page 1 of 2
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