Ericsson DUAL FORMAT MDX LBI-38848A, Maintenance Manual

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GENERAL DESCRIPTION
The Ericsson GE Dual Format MDX

Mobile Radio is
a synthesized, wideband radio that uses integrated circuits
and microcomputer technology to provide high performance
trunked operation. This radio operates in the Enhanced Digi-
tal Access Communications System (EDACS), GE-MARC
trunking environments and in conventional communications
systems. The radio provides 25 Watts of RF power output in
the 806.0125-824.9875 MHz and 851.0125-869.9875 MHz
bands. The receiver operates in the 851.0125-869.9875 MHz
band.
All radio functions are stored in a programmable Elec-
trically Erasable PROM (EEPROM). The radio is field
programmable using an IBM compatible personal computer
with the following equipment:
•
Serial Programming Interface Module TQ3370
•
Programming Cable (19B801417P10) TQ3372
•
MDX Series Programming
Software (EDACS)
TQ3373
•
MDX Series Programming
Software (GE-MARC only)
TQ3346
With the interface equipment and software, the com-
puter can be used to program (or re-program) customer
system frequencies, Channel Guard tones and options. Se-
lection of options is done during radio initialization using
the PC programmer.
The Dual Format MDX

Mobile Radio assembly con-
tains the following circuit boards and assemblies:
•
Power Amplifier Board 19C851822G1
•
RF Board 19D902123G22
•
System Board 19D901891G2
•
Audio/Logic Board 19D903963G1
•
Audio Amplifier Board 19D904025G2
•
Front Cap Assembly 19D904151G1
The circuit boards are all mounted on a main casting to
provide easy access for servicing. Interconnect plugs are
used to connect the boards to eliminate pinched wires and
other wiring problems.
RF BOARD
The RF Board includes the programmable frequency
synthesizer, transmitter exciter, receiver front end and IF
circuitry.
Synthesizer
The synthesizer circuit generates all transmit and re-
ceive RF frequencies. The synthesizer frequency is control-
led by the microprocessor located on the Audio/Logic Board.
Frequency stability is maintained by a temperature compen-
sated reference oscillator module. Transmit audio is proc-
essed on the Audio/Logic Board and applied to the
synthesizer to modulate the VCO and TCXO. The buffered
VCO output drives both the transmitter exciter and the
receiver mixer.
Transmitter
The transmitter consists of a fixed-tuned exciter mod-
ule, a PA module and a power control circuit. The PA module
provides RF output to drive the antenna. The power control
circuit controls the PA module to maintain a constant output
power across the band. The RF output level is internally
adjustable for rated power. Thermistors in the control circuit
protect the PA from overheating by reducing the power
output level.
Receiver
The dual conversion receiver circuit consists of a front
end section, 45.3 MHz first IF, a 455 kHz second IF, and FM
detector. All audio processing and squelch functions are
accomplished on the Audio Board.
POWER AMPLIFIER BOARD
The PA board (19C851822G1) amplifies the RF board
output then connects it back to the RF board where it is
coupled through a PIN diode antenna switch, the low-pass
filter and the directional coupler to provide 25 watts power
output at the antenna connector.
AUDIO/LOGIC BOARD
The Audio/Logic Board provides all audio and digital
processing of the receive and transmit audio for digital
processing by the Logic Board. The board also contains
audio filtering, conventional analog tone processing, and the
receiver squelch. The Audio/Logic Board controls the opera-
tion of the radio and digitally processes the receive and
transmit audio. The board contains a microprocessor and
associated memory circuits including an EPROM for con-
trolling the processor and a programmable "personality"
memory (an Electrically Erasable PROM - EEPROM) to
store customer frequencies, tones and options. The micro-
processor provides control data to the Audio Signal Proces-
sor (ASP), conventional tone generation and detection,
frequency data for the synthesizer, and sends and receives data
to another microprocessor on the Display Board for the LCD.
SYSTEM BOARD
The system board controls the main input power to the
radio. IGNITION SENSE input lead provides the necessary
signals to the MOSFET switching circuit. The board also
interfaces all option connections from the internal boards in the
radio with the optional items outside of the radio. All external
options for the radio, interconnect to the System Board through
the back of the radio using an optional cable.
FRONT CAP ASSEMBLY
The Front Cap Assembly contains the Audio Amplifier
Board. The Audio Amplifier Board provides compression of
the microphone audio. It also provides audio compression for
the received audio in the discriminator and internal/external
speaker audio paths. A 10-watt power amplifier is provided on
the board to drive a 4-ohm internal/external speaker.
ACCESSORIES AND OPTIONS
PC PROGRAMMER OPTIONS
The radio is programmed using an IBM compatible per-
sonal computer equipped with a RS-232 port. Option TQ3370
provides the RS-232 serial interface unit and the cable between
the PC and the unit. An auxiliary power supply for the unit is
also included but is not needed to program the radio.
Option TQ3372 provides the radio programming cable
between the PC interface unit and the radio microphone jack.
MDX PC programming software Option TQ3346 (GE-MARC
only) or TQ3373 (EDACS) is provided in both 3.5 and 5.25
inch diskettes.
PC PROGRAMMED OPTIONS
Carrier Control Timer (CCT)
The Carrier Control Timer turns off the transmitter after
the microphone push-to-talk (PTT) switch has been keyed for
a pre-programmed time period. A pulsing alert tone warns the
operator to unkey and then rekey the PTT to continue the
transmission. The timer can be programmed, using the PC
programmer. Any time periods between 30 seconds and 7.5
minutes can be programmed in 30 second increments. The
timer can be enabled or disabled for each channel.
Channel Guard
Channel Guard provides a means of restricting calls to
specific radios through the use of a Continuous Tone Coded
Squelch System (CTCSS), or a Continuous Digital Coded
Squelch System (CDCSS). Tone frequencies range from 67.0
Hz to 210.7 Hz in 0.1 Hz steps. There are 83 standard PC
programmable digital codes. The Channel Guard tone frequen-
cies and codes are software programmable. Both tone frequen-
cies and digital codes may be used. These codes and
frequencies are listed in Table 1 - Channel Guard Tone
Frequencies and Table 2 - Digital Channel Guard Codes
(see below).
Table 1 - Standard Tone Frequencies (Hz)
67.0 71.9 74.4 77.0 79.7 82.5 85.4 88.5 91.5 94.8 97.4
100.0 103.5 107.2 110.9 114.8 118.8 123.0 127.3 131.8 136.5 141.3
146.2 151.4 156.7 162.2 167.9 173.8 179.9 186.2 192.8 203.5 210.7
To reverse the polarity of the digital Channel Guard
codes in the PC programmer, type I ("inverted") before
the code number, i.e. I023.
NOTE
LBI-38848 LBI-38848
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