Ericsson 19D902304G2 Maintenance Manual

MAINTENANCE MANUAL
MTD™ AND DATA RADIO
900 MHz
AUDIO BOARD 19D902304G2
TABLE OF CONTENTS
DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CIRCUIT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OUTLINE DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
INTEGRATED CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DESCRIPTION
Audio Board 19D902340G2 used with the MTD™ and
DATA RADIO 900 MHz mobile radio provides all Audio,
Data, and Tone processing for the radio except for Volume
Control and Audio Power Amplifier. The Audio Board inter-
faces with the logic board, and receives logic signals from the
microcontroller for RX, Data/Voice, and TX Data muting. The
audio board also contains the receiver squelch circuit with the
internal squelch control. A Block Diagram of the audio board
is shown in Figure 1.
The audio board is mounted in the top front of the radio
housing assembly and connects to the logic board through an
18 pin connector, J703.
The audio board contains the following primary circuits:
•
transmit audio and data
•
receive audio and data
LBI-38546A
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Both the transmit and receive audio and data signals
include tones. A general description of the primary circuit
functions followss.
CIRCUIT ANALYSIS
TRANSMIT AUDIO CIRCUITS
Transmit audio includes voice (microphone path), signal
tones, and 4800 Baud data (MTX). Audio for the transmit
circuit is preemphasized, limited, and coupled through a post
limiter (low pass) filter.
Transmit signal tones that are generated on the logic board are
filtered to remove any voice band harmonics. When the push-
to-talk (PTT) is activated, transmit audio and signal tones are
summed, and then coupled through a modem filter to the
modulator (TX MOD). MTX data is also summed and filtered
in the same circuit for modulation. A Block Diagram of the
transmit audio circuits is shown in Figure 2.
Printed in U.S.A.