Specifications

when the radio is used in a vehicular charger or
repeater.
• Emergency Signalling Feature - Pressing a single
recessed button instantly sends an alert message on a
preprogrammed channel. The radio ID number is
transmitted and the unit is given top priority in the
system. Emergency signalling can also be enabled by
a lanyard connected to the UDC.
• Programmable Carrier Control Timer - A pro-
grammable 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 cir-
cuitry, audio circuitry and the operating controls. The Rear
Cover Assembly houses the RF circuitry which includes the
transmitter, receiver and the frequency synthesizer. The as-
semblies are electrically interconnected by two single-in-
line type connectors. When mated together, the assemblies
form a weather resistant die-cast aluminum case that pro-
tects 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 exter-
nal 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 UHF RF Board, aluminum case, top antenna jack, side
(UDC) antenna jack and various hardware.
The RF Boards 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, 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. During transmitter opera-
tion, 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 de-
tailed circuit analysis, mechanical, outline 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.
ANTENNAS
Antennas are selected based on the operating frequency
range of the radio. Table 1 lists the available antennas which
mount in the antenna jack on the top of the radio. An exter-
nal antenna can be mounted to the unit via the UDC. When
an antenna is connected to the UDC, the antenna on the top
of the radio is disabled.
LBI-33056
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