frequency source or from
a. Modern multichannel communi-
number of sources.
For example, to transmit voice signals
channel modulator must be supplied
signal, all you have to do is apply
with a carrier signal. And to prevent
two signals of different frequencies
to a non-linear device.
carrier signals must be a different
if you apply a 1 kiloHertz (kHz)
frequency and extremely stable.
signal an a 3 kHz signal to the
modulator shown in figure 1, you get
b. In addition to the carrier
signals, a system may also require
(1) 1 kHz.
ringing, and synchronization.
methods used to produce these various
(2) 2 kHz.
signals may vary--it depends on the
(3) 3 kHz.
however, the most practical is a
(4) 4 kHz.
b. The 2 kHz and the 4 kHz
signals are the synthesized signals,
and the other two signals are, of
The word synthesis is derived
course, the two original signals.
from the word synthetic, which means
other words, a synthesized signal is
nothing more than the upper or lower
Synthesis on the other hand
sideband output from a modulating
This is the same principle
parts (elements) that form a whole.
used in communication equipment to
develop all the various signals that
synthesis must refer to the process of
are needed to make the equipment work
obtaining several different synthetic