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.

Inspec keywords: signal processing; modulation; satellite communication; electromagnetic waves; modems

Other keywords: modem; noise; information signal; interference; modulation; electromagnetic wave radiation; radiofrequency signal

Subjects: Satellite communication systems