LESSON 3
IF AMPLIFIERS, LIMITERS, AND DETECTORS
SCOPE.....................................Operation of IF amplifiers; design of IF
stages to achieve the desired gain,
response,
and
selectivity;
use
of
limiters and detectors to reduce noise
and
convert
the
signal
into
audio
variations.
CREDIT HOURS..............................2
TEXT ASSIGNMENT...........................TM 11-668, para 72-81;
Attached Memorandum, para 3-1 thru 3-5
MATERIALS REQUIRED........................None
SUGGESTIONS...............................a. Read the assignment
in TM 11-668
before
you
read
the
attached
memorandum.
b. Note: TM 11-668, page 159, figure 139.
The wave in the lower left side of the
diagram does not represent the IF
signal itself.
The amplitude of this
wave shows the amount of frequency
shift of the IF signal. The actual IF
signal is constant in amplitude but it
varies in frequency.
LESSON OBJECTIVES
When you have completed this lesson, you will be able to:
1.
Determine the response characteristics of transformer coupled amplifiers.
2.
Describe the effects of loading tuned circuits in IF amplifier stages.
3.
Identify and analyze the detectors and discriminators used in FM receivers.
ATTACHED MEMORANDUM
3-1.
IF AMPLIFIERS AND LIMITERS
The circuits employed as IF stages of FM receivers are similar to the ones used
in RF amplifiers (para 1-1 through 1-3). The same coupling arrangements are used
for both IF and RF amplifiers. The major difference lies in the component values
used for the two circuits. The IF amplifiers operate about a center frequency that
is considerably lower than the frequency applied to
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