require variable output signals, as in
these cases any or all three methods
But, all of these methods are divided
may be used, but one or both original
into three general classes as follows:
signal sources must be adjustable.
HOW THE BASIC MODULATION METHOD
This method is the same method shown
in figure 1.
It uses conventional
modulating devices, such as electron
The basic modulation method is
exactly the same process that uses
voice to modulate a carrier signal as
(2) Harmonic Generation Method.
shown by the block diagram in figure
Produces two or more signals from the
same source, then modulates these
signals to produce a large number of
whether the modulator is balanced or
noise free synthesized signals.
For example, if the
modulator in this case is identical to
signals into a balanced modulator are
the one described above.
1 kHz and 3 kHz, then there are only
(3) Heterodyne Method.
(A, fig 2).
However, if the original
a single synthesized signal.
signals are applied to an unbalanced
spurious and unwanted frequencies are
modulator, you get four signals at the
In this case these signals
principle as a filtering process.
are 1 kHz, 2 kHz, 3 kHz, and 4 kHz (B,
b. The method, or combination of
methods used in a specific application
depends on the requirement.
example, if a large number of signals
are required, chances are the harmonic
a. To generate harmonics, you must
generation method is used.
A common method is
required then the heterodyne method is
to apply the signal to an electron
Some applications require many
tube biased to operate as a class b or
multiplex equipment. In these cases
Basis modulation method.