LESSON 3
IF AMPLIFIER AND DETECTOR CIRCUITS
SCOPE ....................................Detection;
IF
amplifier;
IF
tuning;
typical IF circuit; typical detector;
AVC; transistorized IF amplifiers and
detectors.
CREDIT HOURS .............................2
TEXT ASSIGNMENT ..........................TM
11-665,
para
113-114,
135-143;
Attached Memorandum, para 3-1 through 3-3
MATERIALS REQUIRED .......................None
SUGGESTIONS ..............................a. Read assignment in TM 11-665
before
reading attached memorandum.
..........................................b. TM 11-665 considers automatic volume
control
(AVC)
and
automatic
gain
control (AGC) to be one and the same.
The attached memorandum uses the same
approach.
LESSON OBJECTIVES
When you have completed this lesson, you will be able to:
1. Explain the operation of the most frequently used detectors.
2. Explain how AVC or AGC circuits prevent extreme variations in volume although
the received signal is fluctuating in strength.
3. Explain how IF amplifiers are used to provide good selectivity and gain.
4. Explain the operation of transistorized IF amplifiers and detectors.
ATTACHED MEMORANDUM
3-1.
TRANSISTORIZED IF AMPLIFIERS
In AM radio receivers employing electron tubes, the voltage gain of an IF
amplifier can be as high as 100.
However, because the gain of a transistor IF
amplifier stage is only about one-third or one-half that of its tube counterpart,
two or three transistor IF stages are used.
Figure 3-1 shows the circuit of a
transistorized first IF amplifier in an AM receiver.
322 L3
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