Section III. TECHNICAL PRINCIPLES OF OPERATION

TM 11-5805-387-34-2

1-13. REFERENCE DESIGNATIONS AND ABBREVIATIONS

Assembly numbers identify the modem's modules and subassemblies.

Receive audio module

Scope module

Receiver module

Loop battery module

Signal filter subassembly

Meter bias subassembly

Loop connectors filter subassembly

Preregulator subassembly

Similar designators identify module subassemblies:

EXAMPLE: Subassembly A2 of transmitter module A3 is designated A3A2.

Abbreviations of component and subassembly parts complete the full reference designation:

EXAMPLE: Capacitor C1 on subassembly A3A2 is designated A3A2C1.

Section III. TECHNICAL PRINCIPLES OF OPERATION

1-14. GENERAL

The modem consists of a transmit signal path, a receive path, and an associated metering and power supply circuitry.

When the modem is set up for transmit operation, it converts dc mark and space pulses produced by tty equipment into

mark and space tones, which can be transmitted by radio, or over landlines. In voice modes of transmit operation, the

modem combines voice signals with tty (mark and space) tones for simultaneous transmission. The simplified transmit

block diagram is discussed in paragraph 1-15.

When the modem is set up for receive operation, receive mark and space tones are converted into mark and space

pulses suitable for operating receive tty equipment. In voice modes of receive operation, the modem separates voice

signals from tty tones so that simultaneous reception of tty and voice messages is possible. The simplified receive block

diagram is discussed in paragraph 1-16.

The power supply consists of a preregulator, a regulator, and various dc-to-dc inverters that are required to produce the

currents and voltages necessary for operation of the modem. The power supply simplified block diagram is discussed in

Metering and monitoring is accomplished by a front panel meter, a scope, and aural monitoring through headphones or

a monitor speaker. Metering circuitry is discussed in paragraph 1-18.

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