Ericsson DUAL FORMAT MDX LBI-38848D Maintenance Manual

Maintenance Manual

LBI-38848D

DUAL FORMAT MDX



806 - 870 MHz
MOBILE RADIO

TABLE OF CONTENTS

RF BOARD . . . . . . . . . . . . . . . . . LBI-38849

SYSTEM BOARD . . . . . . . . . . . . . LBI-38842

AUDIO/LOGIC BOARD . . . . . . . . . . LBI-38843

AUDIO AMPLIFIER BOARD . . . . . . . LBI-38844

FRONT CAP ASSEMBLY . . . . . . . . . LBI-38850

LBI-38974

PA BOARD . . . . . . . . . . . . . . . . . LBI-38302

SERVICE SECTION . . . . . . . . . . . . LBI-38851

DUAL FORMAT MDX RADIO ASSEMBLY

ISSUE 1

PARTS LIST

ericssonz

Ericsson Inc.

Private Radio Systems
Mountain View Road
Lynchburg, Virginia 24502
1-800-528-7711 (Outside USA, 804-528-7711) Printed in U.S.A.

SYMBOL PART NUMBER DESCRIPTION

APPLICATION ASSEMBLY
19D904183

— — — — ASSEMBLIES — — —
A1 19D902123G22 RF BOARD

A3 19D901891G2 SYSTEM BOARD
A4 19D904025G2 AUDIO AMPLIFIER BOARD
A5 19D903963G1 AUDIO/LOGIC BOARD
19C851822G1 PA BOARD

— — — — — KITS — — — — —
344A4253G1 Hardware Kit (No. 1)

344A4255G7 Hardware Kit (No. 2)
— — — — — CABLES — — — —
19A705301P6 Cable, Antenna

19B801467P1 Cable, J705 to J151
19B801467P2 Cable, J5 to J105
19B801454P36 Cable, RX to J104
19A705235P3 Cable, Ribbon, J901 on Audio Amplifier

to J902 on System Board
19B801454P38 Cable, Antenna to J7
19B801454P37 Cable, TX to J101
19B802397P1 Cable, Handset

— — — MISCELLANEOUS — —
19D904027P1 Casting

19C337683G2 Bracket
19D904185G1 Cover, Bottom
19D904186G1 Cover, Top
19D904187G1 Panel, Front
19B801358P18 Cable, 9 Foot, Power
19B235310P10 Nameplate, Combination

*

COMPONENTS, ADDED, DELETED OR CHANGED BY PRODUCTION CHANGES

Copyright© December 1992, Ericsson GE Mobile Communicat ion s Inc.

TABLE OF CONTENTS

Page

SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

RF BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Synthesizer Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Transmit Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Receiver Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

POWER AMPLIFIER BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

AUDIO/LOGIC BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

SYSTEM BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

FRONT CAP ASSEMBLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

ACCESSORIES AND OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

PC PROGRAMMER OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

PC PROGRAMMED OP TIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Carrier Control Timer (CCT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Channel Gu ard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Squelch Tail Elimination (STE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Retry Opti o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

HARDWARE AND HARDWARE OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

OPTION CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

NOISE SUPPRESSION KIT OPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

POWER CABLE OPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

EXTERNAL SPEAKER OPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

EXTERNAL ALARM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

SYSTEM DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

EDACS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

CONVENTIONAL MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

GE-MARC V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Operational Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Idle Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Ready Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

GLOSSARY OF GE-MARC V SYSTEM TERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

RADIO OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

USER INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

ALERT TONES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

EDACS APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

GE-MARC APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

ASSEMBLY DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

INTERCONNECT DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Back

This manual covers Ericsson and General Electric products manufactured and sold by Ericsson Inc.

NOTICE!

Repairs to this equipment should be made only by an authorized service technician or facility designated by the supplier.
Any repairs, alterations or substitution of recommended parts made by the user to this equipment not approved by the
manufacturer could void the user’s authority to operate the equipment in addition to the manufacturer’s warranty.

NOTICE!

This manual is published by Ericsson Inc., without any warranty. Improve ments and changes to this m anual nec essita ted
by typographical errors, inaccuracies of current information, or improvements to programs and/or equipment, may be
made by Ericsson Inc., at any time and without notice. Such c hanges will be incorporated into ne w editions of this manual.
No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including
photocopying and recording, for any purpose, without the express written permission of Ericsson Inc.

The software contained in this device is copyrighted by the Ericsson Inc. Unpublished rights are reserved under the
copyright laws of the United States.

NOTICE!

LBI-38848D

1

GENERAL DESCRIPTION

The 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 Digital Access
Communications System (EDACS

®

), GE-MARC trunking en­vironments and in conventional communications systems. The
radio provides 25 Watts of RF power output in the 806.01 25-

824.9875 MHz and 851.0125 -869.9875 MHz band s. The re­ceiver operates in the 851.0125-869.9875 MHz band.

All radio functions are stored in a programmable Electri-

cally Erasable

PROM (EEPROM

). The radio is field pro­grammable using an IBM compatible personal computer with
the following equipment:

•

Serial Programming Interfac e 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 computer
can be used to program (or re-program) customer system
frequencies, Channel Guard tones and options. Selection of
options is done during radio initialization using the PC pro­grammer.

The Dual Format MDX Mobile Radio assembly con­tains 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 ar e use d
to connect the boards to eliminate pinched w ires and other
wiring problems.

RF BOARD

The RF Board includes the progr a m mable frequency syn­thesizer, transmitter exciter, recei ver front end and IF circuitry.

Synthesizer

The synthesizer circuit generates all transmit and receive
RF frequencies. The synth esizer frequen cy is co ntrolle d by the
microprocessor located on the Audio/Logic Board. Fre qu e n cy
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 VCO and TCXO. The buffered VCO output driv es both the
transmitter exciter and the receiver mixer.

Transmitter

The transmitter consists of a fixed-tuned exciter module,
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 receiv er 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.

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

1. Do not use 179.9 Hz or 118.8 Hz in areas served by 60 Hz power distribution systems (or 100.0 Hz or 151.4 Hz in areas supplied with 50Hz power). Hum
modulation of co-channel stations may "false" Channel Guard decoders.

2. Do not use adjacent Channel Guard tone frequencies in systems employing multiple Channel Guard tones. Avoid same-areas co-channel use of adjacent
Channel Guard tones whenever possible. As stated in EIA Standard RS-220, there is a possibility of decoder falsing.

3. To minimize receiver turn-on time delay, especially in system using Channel Guard repeaters or receiver voting, choose the highest usable Channel Guard
tone frequency. Do not use tones below 100 Hz when it is necessary to meet the receiver response time requirements of EIA Standard RS-220.

Table 1 - Standard Tone Frequencies (Hz)

SPECIFICATIONS*

GENERAL

Regulatory Approval

FCC (United States) AXATR-311-A2
DOC (Canada) TR-311

Operating Voltage 13.8 Volts ±20%
Battery Drain

Receiver (13.8 Vdc)

Off 0.01 Amperes (maximum)
Squelched 0.75 Amperes (maximum)
Unsquelched 2.0 Amperes (maximum at 10 Watts audio,

External Speaker)

Transmitter (13.8 Vdc) 11 Amperes (maximum at 25 Watts RF)

Channel Spacing 25 kHz (12.5 kHz NPSPAC)
Frequency Stability ±1.5 PPM (±0.00015%)
Temperature Range -30C to +60C (-22F to +140F)
Dimensions (H x W x D)

(Less Accessories)
Height 5.3 cm (2.1 inches)
Width 18.2 cm (7.2 inches)

Depth 24.0 cm (9.5 inches)
Weight 3.0 kg (6.6 pounds)
Antenna Impedance 50 Ohms

TRANSMITTER

Frequency Range 806.0125-824.9875 MHz
Output Power 25 Watts (Intermittent duty cycle; EIA 20%)
Audio Sensitivity 125 mVrms (typical)
Spurious and Harmonics <-16 dBm
Audio Distortion 5% maximum
Modulation Limiting +5 kHz maximum (4 kHz max 821.000 - 824.9875 and

866.000 - 869.9875 MHz)
FM Hum and Noise -45 dB
Audio Frequency Response Within +1, -3 dB of a 6 dB/octave pre-emphasis curve

Per EIA Standards from 300-3000 Hz

RECEIVER

Frequency Range 851.0125-869.9875 MHz
Acceptable Frequency Displacement ±2.5 kHz minimum
Sensitivity (12 dB SINAD) -113 dBm minimum
Spurious Response 70 dB minimum
Adjacent Channel Selectivity 68 dB minimum at ±25.0 kHz
Intermodulation Distortion 65 dB minimum
Audio Frequency Response Within +2, -8dB of a 6 dB/octave de-emphasis curve

from 300 -2700 Hz
Audio Output 10 Watts (External Speaker); 4 Watts (Internal Speaker)
Audio Distortion 5% maximum at 1 kHz

*

These specifications are intended primarily for use by service personnel. Refer to the a ppropriate Specification Sheet
for complete specifications.

LBI-38848D

2

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 opera­tion of the radio and digitally processes the receive and
transmit audio. The board co ntains a microprocessor and
associated memory circuits including an EPROM for con­trolling the processor and a programmable "personality"
memory (an Electrically Erasable PROM - EEPROM) to
store customer frequencies, tones and option s. The micro­processor 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 Amplif ier Bo ard pr ovide s compr essio n of
the microphone audio. It also provide s 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
personal computer equip ped with a RS-232 port. Option
TQ3370 provides the RS-232 serial in terface 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 pr ogramm ing cab le
between the PC interface unit and the radio microphone jack.
MDX PC programming software Option TQ3346 (G E­MARC 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 time r can be enabl ed or disabl ed 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 stand ard
PC programmable digital codes. The Channel Guard tone
frequencies and codes are software programmable. Both
tone frequencies 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.

Squelch Tail Elimination (STE)

STE is used with tone and digital Channel Guard to
eliminate squelch tails. The STE burst is transmitted when
the microphone PTT is released. The receiving radio decodes
the burst and mutes the receiver audio for 250ms. This mute
time allows the transmission to end and to mute the squelch
tail. The radio looks for STE on the received signal when the
microphone is either on or off-hook. The STE is enabled for
transmit and/or recei ve by PC programming the rad i o’s per­sonality.

Retry Option

If no channel is free, the radio can be programmed to
activate the Call Retry state and display ’RETR YING’ in the
display. Retrying causes the radio to revert to Idle mode and
scan for an incoming call while trying to acquire a free
repeater approximately every 5 seconds for a 2 minute pe­riod.

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

PRIMARY
CODE

EQUIVALENT
CODE

PRIMARY
CODE

EQUIVALENT
CODE

PRIMARY
CODE

EQUIVALENT
CODE

023
025
026
031
032
043
047
051
054
065
071
072
073
074
114
115
116
125
131
132
134
143
152
155
156
162
165
172
174
205
223
226
243
244
245

340 766
566

374 643
355

375 707
520 771
405 675
301
603 717 746
470 701
640
360 721
327 615
534 674
060 737
173
572 702
605 634 714
273
333
366 415
233 660
517 741
416 553
354
057
142 270
135 610
350 475 750
104 557
267 342
176 417
370 554

251
261
263
265
271
306
311
315
331
343
346
351
364
365
371
411
412
413
423
431
432
445
464
465
466
503
506
516
532
546
606
612
624
627
631

236 704 742
227 567
213 736
171 426
427 510 762
147 303 761
330 456 561
321 673
372 507
324 570
616 635 724
353 435
130 641
107
217 453 530
117 756
127 441 711
133 620
234 563 621 713
262 316 730
276 326
222 457 575
237 642 772
056 656
144 666
157 322
224 313 574
067 720
161 345
317 614 751
153 630
254 314 706
075 501
037 560
231 504 636 745

632
565
654
662
664
703
712
723
731
732
734
743
754

036
053
122
145
212
225
246
252
255
266
274
325
332
356
446
452
454
455
462
523
526

123 657
307 362
163 460 607
363 436 443 444
344 471 715
150 256
136 502
235 611 671
447 473 474 744
164 207
066
312 515 663
076 203
137

535
525
253
536
542 653
661
425
655
652
550 626
433 552
521
467 511 672
524 765
513 545 564
533 551
472 623 725
647 726
562 645

NOTE:
Primary codes in bold are unique Ericsson codes.

Table 2 - Digital Channel Guard Codes

LBI-38848D

3

HARDWARE AND

HARDWARE OPTIONS

The location and placement of sys tem hardw are option s
are shown on Sheet 4 of the 800 M Hz Dual Format MDX
Mobile Interconnect Diagrams.

OPTION CABLE

Option Cable Option PMCD7Z (19C851585P14) 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.

NOISE SUPPRESSION KIT OPTION

Noise Suppression Kit Option PMPD1A (consisting of
Filter 19A148539G1 and Installation Manual LBI-31363) is
available for installations where excessive alter nator or elec­trical noises, present on the power cable, do not permit the
radio to operate properly. Refer to the interconnect diagram
for the radio and options.

POWER CABLE OPTION

18-foot Power Cable Option PMCD9A,
(19B801358P17), is available for installations requiring
more than the standard 9-foot cable.

EXTERNAL SPEAKER OPTION

External Speaker and Cable Option PMZM1T pro vides
the user with a five-inch waterproof speaker in a LEXAN
housing. PMCC9M is an 18 inch interconnecting cable for
the speaker. The radio’s 10-watt amplifier drives the
speaker’s 4-ohm impedance. The speaker leads are con­nected to pins 2 and 9 of Option Cable Option PMCD7Z
(19C851585P14), using External Speaker Cable Option
PMCC9M (19A149590P8) (18 inches) included in the
PMZM5T kit. A 16-foot cable, Option PMCD1W
(19A149590P10) is also available.

EXTERNAL ALARM

External Alarm Horn Relay Option PMSU1C
(19A705499P1) can sound the vehicle hor n when a call is
received. The option connects to pin 13 of Option Cable
Option PMCD7Z (19C851585P14) and is controlled by a
front panel option switch.

SYSTEM DESCRIPTION

EDACS

The Dual Format MDX mobile radio operates in either
EDACS (digital) mode, or in GE-MARC (tone) mode, pro­viding customers another dimension of flexibility in opera­tion. Both modes provide opportunities to increase RF
channel utilization through faster channel access and the
privacy inherent with selective signalling.

The EDACS system uses 9600 baud, high speed, digital
signalling to identify individual units, user groups, fleets,
and agencies. Agencies contain multiple fleets and fleets
contain multiple user groups (sub-fleets). By using this ad­dressing scheme, lar ge use r g roup s ca n be a cc es se d simu lt a­neously all the way down to individual users. The
programming to determine transmit encoded gr oups and
decoded received groups is contained in the personality
EEPROM of the mobile. This information is individually
programmed to suit each users ne eds via the P C programm er
for the radio.

The typical system configuration consists of at least 2
repeater stations (with a maximum number of 25) and the
associated mobiles. One repeater always is a control ch annel
dedicated to sending out continuous control data and also to
receive channel request data from the mobiles. When a
mobile is first turned on, it scans the available list of frequen­cies programmed in the personality EEPROM for a control
channel. When a control channel is found, the mobile locks
on to the frequency and monitors the data for a channel
assignment (incoming call).

When receiving a channel assignment (incoming call),
the monitoring mobile immediately switches over to the
assigned voice channel and waits for a high speed data
confirmation message. Upon receipt of this message, the
voice paths are unmuted and the user can hear the call.

While on the voice channel, the mobile also continu­ously monitors the low speed, 150 baud (subaudible) data
and carrier noise squelch to ensure consistent operation.
Upon loss of subaudible data reception (i.e., deep fade, or
out-of-range), the mobile returns to the control channel
frequency.

To initiate a call, the user keys the radio (which is locked
to the control channel), and a 30 millisecond high speed data
slotted channel request is transmitted to the control channel
receiver. The control channel processes the request from the
mobile and transmits back a voice channel assignment on an
unused channel.

When all available voice channels are in use, the control
channel places the mobile into a queue, transmits a queue
message back to the mobile, and will give a channel assign­ment to the requesting mobile as soon as a voice channel is
free. If the system is busy and the station queue is filled to
capacity, a system busy message is returned to the requesting
mobile and an alert signal is given to the user.

After the initiating mobile receives a channel assignment
from the control station, it immediately switches frequency
over to the assigned voice channel and sends a burst of 9600
baud dotting. The microphone voice paths are then unmuted
and the transmission begins. The transmitting mobile also
continuously sends out a subaudible tone (along with voice)
for system reliability. If the station loses this signalling, the
voice channel is muted and all receiving mobiles are sent back
to the control channel.

In normal operation, the transmitting mobile sends a high
speed data burst to indicate that the user has unkeyed, causing
all listening mobiles to switch back to the control channel.

CONVENTIONAL MODE

In conventional mode (not trunked) the radio can operate
either with tone Channel Guard, digital Channel Guard, or
carrier squelch, depending on personality programming. Tone
Channel Guard range is 67.0 to 210.7 Hz. Squelch Tail Elimi­nation (STE) is used with Channel Guard to eliminate squelch
tails at the receiving radio by phase shifting the transmitted
Channel Guard tone when the PTT is released.

Direct mode works identically to conventional mode ex­cept that the transmit frequency band is changed to 851 to 870
MHz to permit direct mobile-to-mobile communications.

GE-MARC

The

GE-MARC

trunked mobile radio system consists of
a repeater for each channe l and the u sers’ mobile radio units.
The system uses tone signalling with each mobile being as­signed two and/or four tone group tone sequences. Groups of
mobiles are assigned the same tones so that any unit can talk
to all other units in the same grou p. A block diagram of th e

GE-MARC MDX

is shown in Figure 1.

When originating a call, the mobile identifies an idle

repeater channel and interrogates it with a single burst of

"busy"

tone; the repeater keys its transmitter and sends a burst

of

"acquisition"

tone back to the mobile unit. When the
interrogating mobile detects the acquisition tone, it then trans­mits its collect and group tones which the repeater regenerates
for all idle mobile units in the system.

The idle mobiles, which continually scan all channels, will
stop on the active channel if any of the programmed collect
tones are detected and wait for group tone(s).

If the correct tone sequence is detected, the mobiles will
alert the operator of an incoming call and open their audio
circuits. If the correct sequence is not detected, the idle mobiles
will resume scanning the channels. Once the mobile is

"locked"

on a channel, it will remain there until the repeater

times out or the operator terminates the call.

Operational Modes

The radio will always be in one of three operational modes:
Idle, Wait, or Ready. The three operational modes and the

conditions that cause the radio to switch from one mode to
another are shown in Figure 2.

The radio enters the Idle mode when power is turned on
and begins scanning channe ls for incoming calls. The Wait
mode is entered when the user places a ca ll. Th e radio rem ains
in the Wait mode until a channel is acquired, or if no channel
is available. The Ready or Conversation mode is indicated by
an alert tone and the mode indicator on the control panel. A
signal timing diagram is shown in Figure 3.

Idle Mode

When the radio is in the Idle mode, the audio is muted and
all channels programmed for call decode are sequentially
scanned for an incoming call. An incoming call is identified by
detecting one of the collect tones programmed in the area.
Upon receipt of a collect tone, the mobile looks for a short
interval for the group or individual tones providing that their
collect tones are the same. When no valid tone is found, the
mobile will resume scanning the channels for an incoming call.

If a group (or individual decode) tone is detec ted, the
mobile then looks for busy tone for a 90 millisecond period. If
four tones are properly decoded, the mobile will then look for
busy tone for 270 milliseconds.

When no valid tones are found, the mobile will resume
scanning for a call with the next channel. When a busy tone is
found, the mobile will enter the Ready mode. If busy tone is
not detected, the mobile remains in the Idle mode and continues
scanning channels looking for an incoming call.

Removing the handset from the hang er, pressing th e PTT
switch or pressing the SEND key on the handset will cause the
radio to enter the Wait mode.

Wait Mode

When the user enters the Wait mode, the display group is
checked to make sure it is a valid call-originate group. If it is
not valid, a low-frequency tone is heard for one second. If va lid,
the radio will scan the call-originate frequencies for brief
intervals until it finds one with no busy tone on it. If no channel
is free, the radio, if programmed for this option, will activate
the Call Retry state and display "

RETRYING

" in the display.
Retrying will cause the radio to revert to the Idle mode and scan
for an incoming call while trying to acquire a free repeater
approximately every 5 seconds for a 2 minute period. If the
Retry option is not enabled, the mobile will sound the low-fre­quency tone and then return to the Idle mode and display

"BUSY".

If a channel with no busy tone is found, the mobile trans­mits a burst of busy tone to acquire the repeater. The repeater
then responds with a burst of acquisition tone. Upon receipt of
the acquisition tone, the mobile proceeds to transmit the group
tones (either two or four tones). If a four-tone sequence is sent,
the mobile must detect all four tones and busy tone before
entering the Ready mode. If a two-tone sequence is sent, the
busy tone must be present within 90 milliseconds of the last

LBI-38848D

4

tone in order for the radio to enter the Ready mode. If no busy
tone is present or if the four-tone sequence isn’t valid, the
mobile will jump to the next channel in the call originate set
and check for busy tone as described above.

Ready Mode

When an incoming call has been detected or an idle chan­nel has been acquired, the mobile enters the Ready mode. In
this mode, the audio and push-to-talk circuits are enabled, the
speaker is unmuted, and the operator is alerted by an alert tone.
The radio can then be used in the conventional push-to-talk
manner with the radio remaining on the channel until the
operator hangs up or the repeater drops the busy tone causing
the unit to revert to Idle mode.

GLOSSARY OF GE-MARC TERMS
Idle Mode

In the "standby" condition, the mobile is inactive but

prepared to call or be called. The trunked radios are IDLE
until they are turned off.

Wait Mode

In the "attempting origination" condition, the Wait

mode is entered from Idle mode (only) a s the user presses
the PTT switch on the microphone, or comes "off-hook".
If successful, the unit becomes READY. Otherwise, the unit
is IDLE or IDLE/WAIT after all channels are tried.

Ready Mode

In the "operating" condition, Ready is entered from

Idle mode via Wait mode when calling or directly from Idle
when called. Ready mode ends (the radio reverts to Idle)
when the user disconnects or with the loss of received Busy
Tone from the repeater. This normally occurs when the
repeater shuts down after communication is completed.

Busy Tone

A "Voice-plus" tone of 3051.9 Hz is the standard busy

tone. The 2918 Hz is the alternate busy tone. The busy tone
modulates mobile and repeater transmitters at a low level of
1 kHz deviation continuously. This tone is filtered out of the
received audio and is used to hold the communication chan­nel active. It also excludes other mobiles from using the
channel when a call is active.

Acquisition Tone

A 1962.9 Hz tone sent at full deviation for 50 millisec­onds from the repeater is used as acknowledgment from the
repeater that a busy tone was sent and signals the mobile that
signalling tones can now be sent.

Collect Tone

A tone chosen from 34 standardized frequencies, rang­ing from 508.6 Hz to 2792.4 Hz, is used as the first tone in
the group tone sequence. The collect tone is used to gather
all mobiles with the same collect tone for decoding a call.
The duration of the tone varies as a function of the number
of channels which are programmed into the mobile and/or
repeater.

If a call is initiated and a sequence of five beeps is sounded,
the user cannot access the radio system because the mobile
is out of receive range or is inoperative. Any subsequent
call will be ignored for 20 seconds.

NOTE

Figure 3 - Signal Timing Figure 1 - GE-MARC Block Diagram

Figure 2 - GE-MARC Operational Modes

LBI-38848D

5

In a two-tone call, the mobile sends the collected tone
for a programmable duration. In the four-tone call, the mo­bile always sends a 90-millisecond collect tone which the
repeater regenerates and sends for the correct duration.

Group/Individual Tones

Group/Individual Tones chosen from the 34 standard
frequencies follow the collect tone. In a two-tone call, the
second tone is sent for 450 milliseconds. In a four-tone call,
the second, third, and fourth tones are sent for 90 millisec­onds from the mobile and 180 milliseconds from the re­peater.

RADIO OPERATION

A complete set of operating instructions for the Dual
Format MDX are provided in LB I-38846 and ar e provided
with each radio.

This radio is flexible in operation and can be used in any
of three operating modes: Conventional radio system, En­hanced Digital Access Communications (EDACS) system,
or GE-MARC (tone controlled) system. Either of the latter
two systems provide trunked channel selection for increased
channel utilization.

In an EDACS trunked environment, the user selects a
communications system and group. In this mode, audio
channel selection is transparent to the user and is controlled
via digital communication with the system controller. This
mode incorporates advanced programmable features and fast
access to communication channels.

In a GE-MARC trunked environment, the user selects a
communications area and grou p. In this mode, audio channe l
selection is also transparent to the user and is controlled via
tone signalling.

In Conventional mode, th e user selects a chan nel and
communicates on that channel. In this mode, a system r efers
to a set of channels and a channel is a transmit/receive radio
frequency pair.

The exact operation of any radio depends upon the
operating mode, the programming of the radio and the par­ticular radio system. Most features described in the se oper ­ating instructions can be enabled or disabled through
programming. Both of these important factors must be con­sidered when addressing the following instructions.

USER INTERFACE

Operating controls are located on the radio front panel
and microphone.

The front panel LCD provides radio status and commu­nication control information to the operator. The keypad is
used for manual num b er en t ry f or in divi du al ca ll s ac ce ss to
a telephone interconnect system and activation of various
EDACS, GE-MARC, and conventional features.

Turning The Radio ON/OFF

The radio is turned ON/OFF by pressing the PWR

button in the upper left corner of the front panel. A self
diagnostic test is performed when the radio is first turned on
if enabled through programming. To turn the radio OFF,
press the PWR button again.

ALERT TONES

The Dual Format MDX radi o generates a set of unique

alert tones to indicate operating status. The following section
identifies and describes the alert tones used in the Dual
Format MDX radio for Conventional, GE-MARC, and
EDACS applications.

EDACS APPLICATIONS

CALL
ORIGINATE
ALERT

If programmed, a short tone is sounded
whenever the Push-To-Talk key is
pressed and the radio has acquired a
channel. This tone indicates the user can
begin communications.

CALL QUEUED If on e short, high-pitched tone sounds

after the transmitter is keyed, this indi­cates that the system has placed the re­quest in a queue. This tone sounds at both
the transmitting unit and the receiving
unit(s) indicating to the user on the re­ceiving end that a call is being directed
to them. If the PTT is unkeyed while in
the queue, the radio autokeys (automat­ically keys) Push-To-Talk when a chan­nel becomes availa ble (see AUTOKEY).

AUTOKEY When the PTT is keyed to place a call on

the system, but the PTT is released be­fore getting to the channel (e.g. a queued
call), the radio automatically keys on the
channel when it gets the assignment. The
radio generates a long beep and holds the
transmitter keyed for two seconds. Press­ing the PTT button keeps the channel and
sends the message before this two sec­ond time-out has expired.

SYSTEM BUSY If you press the PTT key and hear thre e

short, medium-pitched tones, this indi­cates that the receiving party is already
on the system or the system is busy and
its queue is full. You must rekey later to
access the system.

CALL DENIED A single, low-pitched beep sounds when

the PTT key is pressed and the request is
denied by the system. This happens if the

unit is an invalid user or if the unit is
requesting an unavailable service.

OUT-OF­RANGE/
SYSTEM
INOPERATIVE

A single, low-pitched tone sounds immedi­ately after the PTT key is pressed indicat­ing the radio is out of range of the repeater.
The radio tries to place the call for a short
period (3 seconds) after the initial attempt.
The radio generates a second low-pitched
tone when it gives up trying to place the
call. These tones are also heard if the sys­tem is off the air or the radio needs servic­ing (even when the radio is within calling
range of the repeater).

GE-MARC APPLICATIONS

CALL
RECEIVED
ALERT

If programmed, a single alert tone sounds
when a group call is received and a two­tone alert (one high followed by one low
tone) sounds for an individual call.

CALL
ORIGINATE
ALERT

WAI T momentar ily displays when a call is
being placed. Then a three-tone alert is
sounded to indicate the call origination is
complete. This indicates a channel was ac­quired and is ready for norm al conversa­tion.

INVALID CALL
ORIGINATE
ALERT

A low-frequency tone is sounded for one
second immediately after pressing PTT and
the display does not show WAIT. This in­dicates a call was attempted within a group
that is not enabled for call originate or an
invalid dispatch overdial call was at­tempted.

SYSTEM
TONES

A low-frequency tone is sounded for one
second after attempting to place a trunked
call and BUSY is displayed. This indicates
that the GE-MARC system is busy. If the
"Call Retry" option has been enabled
through programming, the radio retries at
5 second intervals up to 15 times unless
END is pressed, a channel is acquired, or
an out-of-range condition occurs.

OUT-OF­RANGE
ALERT

If NO SVC is displayed a nd five beeps are
sounded after attempting to place a trunked
call, the radio is out of range of the GE­MARC system. If the beeps sound when
the radio is within known range of the
system, the radio may need servicing. If the
"Call Retry" is active, the radio tries the
channel at twenty second intervals for five
minutes.

CARRIER
CONTROL
TIMER

(GE-MARC and Conventional operation.)
A pulsed-tone signal is sounded for a pre­programmed time after PTT is pressed. Af­ter nine seconds of pulsing the alert tone,
the radio unkeys the transmitter and com­munications are interrupted. While the tone
is pulsing, the user can release and press
PTT again to reset the timer and resume the
conversation. In the conventional mode,
the radio unkeys and beeps until PTT is
released.

SYSTEM
TONES

The GE MARC radio may gene rate other
system tones to alert the user of custom
programmed events. Contact the GE­MARC system operator for details about
these alert tones.

LBI-38848D

6

ASSEMBLY DIAGRAM

(19D904183, Sh. 1, Rev. 17)

LBI-38848D

7

ASSEMBLY DIAGRAM

(19D904183, Sh. 2, Rev. 17)

(19D904183, Sh. 5, Rev. 17)

LBI-38848D

8

INTERCONNECTION DIAGRAM

(19D904133, Sh. 1, Rev. 3)

LBI-38848D

9

INTERCONNECTION DIAGRAM

(19D904133, Sh. 2, Rev. 2)

LBI-38848D

10

INTERCONNECTION DIAGRAM

(19D904133, Sh. 3, Rev. 2)

LBI-38848D

11