SECTION 2 · THEORY OF OPERATION
2-1 INTRODUCTION
This se�tion provides a functional description of the circuitry con
tained in the FM/AM-500A Communications Service Monitor on the follow
ing levels. Detailed module level theory of operation is contained in
Section 7.
2-1-1 SIMPLIFIED THEORY OF OPERATION
Paragraph 2-3 provides a simplified description of the signal flow
through the appropriate modules within the FM/AM-500A according to the
operating mode. This description is based on the FM/AM-500A Simplified
Block Diagram shown in Figure 2-2.
2-1-2 INTERMODULE SYSTEMS THEORY OF OPERATION
Paragraph 2-4 provides system-oriented theory of operation for func
tions involving two or more modules. Block diagrams accompany each
discussion to depict the interactivity of the several circuits uti
lized.
2-2 GENERAL
The FM/AM-500A's modular design allows electronic circuits to be iso
lated within the mechanical assemblies for ample shielding and ease of
maintenance accessibility, yet minimizing space and interconnection
requirements. Except for AC and DC power connectors and a 10 MHz RF
connector on the Rear Panel, all controls, indicators and connectors
are mounted on the Front Panel. The main power transformer, AC voltage
select switch and power fuses are also mounted on the Rear Panel. All
other components are contained within the modules listed below accord
ing to mechanical characteristics, not functional relationships, one
with another. Figure 2-1 identifies these modules.
2-2-1 OPEN PC BOARDS
1. Power Supply - Provides regulated +12 VDC, -12 VDC, +5 VDC, and
unregulated +43 VDC for set operation and current-regulated
+15 VDC for battery charging.
2. Frequency Standard - Provides precise reference frequencies for
various modules.
3. Receive Audio Board - Controls squelch level and bandwidth of
demodulated audio signals and directs the signal to subsequent
monitoring and analysis functions.
4. Generate Audio Board - Converts audio frequency into a modula
tion voltage.
2-1
Содержание FM/AM-500
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