Specifications

DESCRIPTION
The UHF MDX Mobile Radio is a synthesized, wide
band radio that uses integrated circuits and microcomputer
technology to provide high performance in conventional com-
munications systems. The UHF MDX Mobile radio provides
40 Watts of RF power output in the 403-440, 440-470 or 470-
512 MHz bands.
All radio functions are stored in a programmable Electri-
cally Erasable
PROM (EEPROM)
.
• Serial Programming Interface Module TQ3370
• Programming Cable (19B801417P10) TQ3372
• MDX Series Programming Software TQ3346
With the interface equipment and software, the computer
can be used to program (or re-program) customer system fre-
quencies, and options. Selection of options is done during ra-
dio initialization using the PC programmer.
The UHF MDX Mobile Radio assembly contains the fol-
lowing circuit boards and assemblies:
• Power Amplifier 19D904792
• RF Board 188D5062
• System Board 19D901891
• Audio/Logic Board 19D903963
• Audio Amplifier Board 19D904025
• Front Cap Assembly 19D904151
The circuit boards are all mounted on a main casting to pro-
vide 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 syn-
thesizer, transmitter exciter, receiver front-end and
I
ntermedi-
ate
F
requency (
IF
) circuitry.
Synthesizer
The synthesizer circuit generates all transmit and receive
RF frequencies. The synthesizer frequency is controlled by the
microprocessor located on the Audio/Logic Board. Frequency
stability is maintained by a temperature compensated reference
oscillator module. Transmit audio is processed on the
Audio/Logic Board and applied to the synthesizer to modulate
the
V
oltage
C
ontrolled
O
scillator (
VCO
) and the
T
emperature
C
ontrolled
X
tal (crystal)
O
scillator (
TCXO
). The buffered
VCO output drives both the transmitter exciter and the receiver
mixer.
Transmitter
The transmitter consists of a fixed-tuned exciter module,
PA module and a power control circuit. The PA module pro-
vides RF output to drive the antenna. The power control circuit
controls the PA module to maintain constant output power
across the band. The RF output level is internally adjustable for
rated power. A thermistor control circuit protects the PA from
overheating by linearly reducing the power output level with
increasing temperature.
Receiver
The dual conversion receiver circuit consists of a front-end
section, 45 MHz first IF, a 455 kHz second IF and
F
requency
M
odulation (
FM
) detector. All audio processing and squelch
functions are accomplished on the Audio/Logic Board.
POWER AMPLIFIER BOARD
The PA Board amplifies the RF board output, then connects
it back to the RF board where it is coupled through a
PIN
di-
ode antenna switch, a low-pass filter and a directional coupler
to provide 40 watts power output at the antenna connector.
AUDIO/LOGIC BOARD
The Audio/Logic Board provides all audio and digital proc-
essing of the receive and transmit audio for digital processing
by the Logic Board. This board also contains audio filtering,
conventional analog tone processing and the receiver squelch.
The Audio/Logic Board controls the operation of the radio and
digitally processes the receiver and transmit audio. The board
contains a microprocessor and associated memory circuits in-
cluding an
E
lectrically
P
rogrammable
R
ead
O
nly
M
emory
(
EPROM
) for controlling the processor and a programmable
"
personality
" memory, an EEPROM to store customer fre-
quencies, tones and options. The microprocessor provides con-
trol data to the
A
udio
S
ignal
P
rocessor (
ASP
) conventional
tone generation and detection, frequency data for the synthe-
sizer and sends and receives data to/from another microproces-
sor on the Display Board for the alphanumeric LED display.
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.
The Front Cap Assembly also contains the display board
which includes the LED Display, the keyboard and inter-
face/drive circuitry. In Scan models the internal speaker is
mounted in the front cap. In System radios there is no
speaker, to allow room for the additional keys.
SYSTEM BOARD
The system board controls the main input power to the
radio. The
IGNITION SENSE
input lead provides the nec-
essary 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 ra-
dio. All external options for the radio, interconnect to the
System Board through the back of the radio using an op-
tional cable.
ACCESSORIES AND OPTIONS
PC PROGRAMMER OPTIONS
The radio is programmed using an IBM compatible
P
er-
sonal
C
omputer (
PC
) equipped with an RS-232 serial inter-
face 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 MDX UHF radio program-
ming cable between the PC interface unit and the radio mi-
crophone jack.
PC PROGRAMMED OPTIONS
Carrier Control Timer (CCT)
The Carrier Control Timer turns off the transmitter after
the microphone PTT switch has been keyed for a pre-pro-
grammed time period. A pulsing alert tone warns the opera-
tor to unkey and then key again the PTT to continue the
transmission. The timer can be programmed, using the PC
programmer. Any time period between 0 seconds and 4.1
minutes can be programmed in 10 second increments. The
timer can be enabled or disabled for each channel.
HARDWARE AND HARDWARE
OPTIONS
The location and placement of system hardware options
is shown on the MDX Conventional Mobile Radio Intercon-
nection Diagram 188D5198.
OPTION INTERFACE CABLE
Option Interface Cable (19C851585P18) is used to bring
all option connections from the System Board through the
back of the radio to the outside. This cable is required with
all external options. Option Interface Cable
(19C851585G14) can be used for all external options except
data.
NOISE SUPPRESSION KIT
Noise Suppression Kit consists of filter 19A148539G1
and Installation Manual LBI-31363. This kit is available for
installations where excessive alternator or electrical noises,
present on the power cable, do not permit the radio to oper-
ate properly. Refer to the Interconnect Diagram for the radio
and options.
POWER CABLE
The 18-foot Power Cable (19B801358P17) is available
for installations requiring more than the standard 9-foot ca-
ble.
EXTERNAL SPEAKER
External Speaker and Cable provides the user a 5-inch
waterproof speaker in a LEXAN housing (19A149590P1),
an 18-inch, external speaker cable (19A149590P8) is in-
cluded. A 16-foot cable (19A149590P10) is also available.
When using the external speaker, the internal speaker
should be disconnected. The internal/external speaker switch
option PMPL3D allows use of both speakers (Refer to the
Interconnection Diagram).
EXTERNAL ALARM HORN RELAY
External Alarm Horn Relay (19A705499P1) can sound
the vehicle horn when a call is received. The option connects
to Pin 13 of cable (19C851585P14) and is enabled through
the front panel switch.
LBI-33055
3