
CHAPTER 15
Modulation
15.1 The Need for Modulation
We have now reached the point—in theory at any rate—at which we
can generate a continuous stream of waves of constant frequency.
This,
however, is completely useless for communication of
messages, let alone speech, music or pictures. It merely establishes a
link between sender and receiver, and to effect communication via
the link some kind of organised change is needed. The technical
word for it is modulation. The raw material that we have provided
ready for modulation is called the carrier wave, although really it is a
continuous succession of waves.
15.2 Amplitude Modulation
As a simple