Ericsson EDACS M-PA 806-870 MHz, Руководство по обслуживанию, Страница: 6 / 14

transmitted and the unit is given top priority in the
system. Emergency signalling can also be enabled by
a lanyard connected to the UDC. The radio supports
GE-STAR emergency signalling for conventional
mode operations.
•
Programmable Carrier Control Timer - A
programmable transmit timer will automatically
disable the transmitter and provide an alerting tone
after time-out. This feature prevents radio damage and
unnecessary channel traffic in the event of a "stuck"
mic. The CCT is reset on every PTT.
•
Programmable Transmit Power Level - Transmitter
power level is PC programmable into the radio (high
or low) on a per channel basis.
•
Automatic Squelch - Squelch operation in trunked
mode is automatically controlled. In conventional
mode, squelch threshold can be programmed on a per
channel basis. Squelch circuits are designed so that
annoying squelch pops, which may occur at the end
of a received message, are minimized.
•
Alert Tones - Alert tones prompt the operator of
various radio conditions such as channel access, CCT
time-out or a low battery.
•
Power-Up Self-Test - At power-up the radio
automatically performs a diagnostic test on itself and
reports any found errors via the LCD.
DESCRIPTION
Two major assemblies form an M-PA radio. The Front
Cover Assembly contains all of the microprocessor circuitry,
audio circuitry and the operating controls. The Rear Cover
Assembly houses the RF circuitry which includes the trans-
mitter, receiver and the frequency synthesizer. The assem-
blies are electrically interconnected by two single-in-line
type connectors. When mated together, the assemblies form
a weather resistant die-cast aluminum case that protects the
radio’s circuitry from harsh outside environments.
Power is provided by a battery pack that slides and
locks on to the bottom of the radio. The radio’s on/off
switch is located on the battery pack. Battery packs are
available in several different sizes and capacities.
The antenna screws on to the top of the unit. A side an-
tenna connection is also provided at the UDC for an external
antenna or for test purposes. This UDC antenna connection
is also utilized for external antenna operation when the radio
is locked in the vehicular charger or repeater.
REAR COVER ASSEMBLY
The Rear Cover Assembly houses the RF Board in the
die-cast aluminum case. The complete assembly consists of
the 800 MHz RF Board, aluminum case, top antenna jack,
side (UDC) antenna jack and various hardware.
The RF Board’s circuitry includes the transmitter, re-
ceiver and the frequency synthesizer. This FM circuitry is
under complete control of the microprocessor circuits. Con-
trolling data sent to this assembly from the Control Board
includes serial synthesizer data loading, band switch data,
transmitter/receiver enabling and a transmitter power level
signal. The RF Board outputs the demodulated audio/data
and a synthesizer lock status line to the Control Board. Dur-
ing transmitter operation, the RF power appears at the top
antenna jack (or the UDC jack if the appropriate adapter
plug is inserted). The Rear Cover Assembly maintenance
manual contains a detailed circuit analysis, mechanical, out-
line and schematic diagrams for this assembly.
FRONT COVER ASSEMBLY
The Front Cover Assembly houses all of the operating
controls and the digital control circuitry for the radio. Board
assemblies used in this assembly include the Control and
LCD Boards and flex circuits include the Keypad, UDC and
Speaker Flex circuits. The speaker, microphone and Battery
Plate are also a part of this assembly. The complete assem-
bly is housed in the die-cast aluminum front cover. Scan and
System model radios are equipped with a keypad on the
front panel.
The Control Board located in the Front Cover Assembly
is the largest and most complex board in the Front Cover
Assembly. It contains all microcomputer and audio circuitry
which controls the radio. See the maintenance manuals spe-
cific to the Control Board or the Front Cover Assembly for
service information on the related assembly.
LBI-38460
6