Comnet LBI-38435B, Руководство по обслуживанию

Страница: 6 / 21

LBI-38435B
6
DESCRIPTION
The Com-Net Ericsson MLS series mobile radio is a
synthesized, wide-band radio, utilizing microcomputer
technology to provide high reliability, high quality, and
high performance in two-way, FM, mobile
communication. The MLSL161 and MLSL261 radios
operate in the 29.7 to 42 MHz and the 42 to 50 MHz
frequency ranges respectively and provide an RF power
output of 60 watts with an allowable channel separation
of 1 MHz transmit and 1 MHz receive.
The small size of the MLS makes it ideal for front
mounting in conventional vehicles, with all operating
controls and indicators located on the Control Panel. The
standard radio with Control Panel is equipped with the
following:
•
Microcomputer control
•
RF channel synthesizer
•
Up to 16 RF channels
•
LED channel display
•
Channel Guard (CTCSS or DCG)
•
Carrier Control Timer (CCT)
•
+ 0.0005% (5 PPM) frequency stability
The radio circuitry consists of a System Control
Frequency Synthesizer Board (A801), a
Transmitter/Receiver Board (A802) and a Front
Panel/Control Unit (A803 and A804).
The circuitry also consists of Control Indicator Panel
(A804), an internal speaker, an antenna jack, a connector
for the microphone, and a power supply cable (refer to
Figure 1 – Mobile Layout Diagram).
No power supply is used since the highest supply
voltage required for the operation of the radio is provided
by the vehicle battery. The radio is designed for
operation in a 12-volt, negative ground, vehicular system
or as an AC-powered mobile.
Access to each circuit board is easily achieved by
loosening four (4) screws in the rear of the top and bottom
covers, then removing each cover. All tuning controls are
also accessible with the covers removed.
Access to the Control and Indicator circuitry can be
achieved by removing the four (4) screws securing the
front panel to the chassis.
Transmitter
The Transmitter circuit consists of a broadband,
fixed-tuned driver module and a power amplifier.
The RF power output level is internally adjustable for
rated power output. Once the level is set, a sensing
control circuit holds the power constant over the
temperature and/or voltage variations within specified
limits.
Receiver
The dual conversion receive circuit consists of a
29.7–42/42-50 MHz front end section and two mixer/IF
sections operating at 20.8 MHz and 455 kHz. The receive
circuit also contains a squelch and audio section. The
audio section provides a 4-Watt audio output into a 4-ohm
load (internal speaker or external speaker).
Frequency Synthesizer
The synthesizer drives the transmit circuit exciter and
the receive circuit first mixer and consists of a synthesizer
chip, a prescaler, a reference oscillator, and the voltage-
controlled oscillators (VCOs). The synthesized frequency
is controlled by the personality EEPROM and applied to
the Transmitter/Receiver board.
An Electrically Erasable PROM (EEPROM), on the
System Control and Frequency Synthesizer Board (A801)
stores the binary data for the transmit and receive
frequencies, Channel Guard tones, digital codes, and CCT
timing periods. The EEPROM is field programmable and
each channel can be individually programmed or
reprogrammed for the desired transmit and receive
frequencies, CG tones, and digital codes or CCT timing.
Control Panel
The Control Panel consists of the front panel housing
an internal speaker and a plug-in module (A804) which
determines the number of channels (2 to 16) and mode of
operation (with or without scan). Refer to Maintenance
Manual LBI-38424, listed in the Table of Contents of this
publication. The panel is made of highly durable plastic
with rounded corners and recessed controls, and
indicators for passenger safety requirements (refer to the
OPERATION section for a description of the Control and
Indicator functions).