ABSTRACT
It is often the case in instrumentation and communication systems that an information-bearing signal may not be in an optimal form for direct use. In such cases, the information-bearing signal may be used to alter some characteristic of a second signal more suited to the application. This process of altering one signal by means of another is known as
modulation
; the original information is called the
baseband signal
, and the signal modulated by the baseband signal is termed the
carrier
(because it “carries” the information). Recovery of the original information requires a suitable demodulation process to reverse the modulation process.
