(2) The discriminator is a frequency detector. The center frequency of the
discriminator is the same as the IF. Any deviation from this frequency
(above or below) will be detected, and the discriminator will produce a
voltage proportional to the amount of deviation.
This voltage is
filtered to eliminate the IF carrier, leaving only the dc voltage
variation to be amplified by the audio stages.
The output of the
discriminator is considered to be the AF component of the dc voltage.
In modern communication, it is common practice to simultaneously transmit
several hundred telephone messages over one radio channel.
interference, each telephone message must have its own carrier signal. Each signal
requires a different frequency which must be extremely stable. The most practical
a. Frequency Synthesis Methods.
is shown in figure 2-18.
used to synthesize signals follows this principle.
Some of the various methods
used to synthesize frequencies are circuits designed to add, subtract, multiply,
and divide a stable basic frequency.
b. Uses For Synthetic Frequencies.
The signals that are produced by
They may be used as
carrier frequencies, testing signals, synchronizing signals, or as alarm or ringing
The intended use of the signal will in many cases determine which of
several methods will be used to synthesize the signals.
Basic frequency synthesis principle.