RELM BK RADIO SDMX920 User manual

Base Station and Repeater
SMX920
SDMX920
VER. 1.1.4
0300-30973-700_REV 07-14

Technical Manual
MX920 Base Station & Repeater
i
© SPECTRA ENGINEERING 2003 Revision 1.1.4
RELM
Wireless C o r por a t ion
7100 Technology Drive
West Melbourne, FL 32904
Front Desk: (321)
984-1414
Sales: [phone]
Service: (800)
422-6281
www.RELM.com
In order to continually improve our products, Spectra Engineering Pty Ltd reserves the right to
alter, without notice and at any time, the equipment and specifications described in this
document.
All performance figures quoted are typical and are subject to normal manufacturingand
service tolerances.
The purchaser is warned that some statements made in this document may be inaccurate due to
typographical or other errors or subsequent modifications of the product. While every care has
been taken in the creation of this document, no warranty of accuracy or reliability is given, in
any advice or information contained in this document. Spectra Engineering Pty Ltd or any
director, officer, agent or employee of Spectra Engineering Pty Ltd cannot be held liable
for any
loss or damage whatsoever arising in any way or any representation,act or omission whether
express or implied (including responsibility to any person by reason of negligence).
Copyright © Spectra Engineering Pty Ltd 1997
This work is copyright. Other than as permitted by Law, no part of it may be reproduced,
stored in a retrieval system or transmitted in any form or by any process without prior written
permission.
FCC Interference
Warning
Note: The equipment has been tested and found to comply with the limits for a class B digital
device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable
protection against harmful interference when the equipment is operated in a commercial or
residential environment. This equipment generates, uses and can radiate radio frequency
energy. If not installed and used in accordance with this instruction manual, may
cause
harmful
interference to radio communication.

MX920 Base Station & Repeater
Technical Manual
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Technical Manual
MX920 Base Station & Repeater
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© SPECTRA ENGINEERING 2003 Revision 1.1.4
Record Of Changes
Any changes to this manual are recorded on this list. Spectra Engineering may issue
replacement pages to you from time to time. If any updates are issued, you will also
receive a replacement for this page.
Date Version Chapter Changes Pages Changed
Mar 2003 1.0.0 All - Initial Release All
June 2004 1.1.0 General Revision All
Sept 2004 1.1.1 Changes to Table 8-4 Rs232 Pin
configuration 33
19/10/06 1.1.2 Added Screw Head Types section
2.2 8
22/01/07 1.1.3 Updated RJ45 line level spec's 33
21/01/07 1.1.4 Updated Calibration Section 7 29

MX920 Base Station & Repeater
Technical Manual
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© SPECTRA ENGINEERING 2003 Revision 1.1.4
SAFETY SUMMARY
Only the MX920’s self contained power supply, if installed, contains dangerous mains
voltages within. Normal operation and use of the MX920 does not expose the operator or
service technician to high voltage parts. The power supply is isolated from and maybe
removed safely from the main chassis. For servicing, please return to your nearest
distributor. No fuses or user-serviceable parts are within the power supply module.
The following general safety precautions as would normally apply, should be observed
during all phases of operation, service and repair of this equipment.
AROUND THE EQUIPMENT
To minimise any possible shock hazard from an external power supply or lightning strike, the
chassis or equipment cabinet must be connected to an electrical ground. This is normally
achieved by the Earth grounding wire within the 3 wire mains cable. Provide adequate
ventilation around the rear of the equipment.
DO NOT OPERATE IN AN EXPLOSIVE ATMOSPHERE
Do not operate the equipment in the presence of flammable gases or fumes. Operation of
any electrical equipment in such an environment constitutes a definite safety hazard.
DO NOT ATTEMPT INTERNAL SERVICE WHILE TRANSMITTING
Thermal or RF burns may result from touching certain components within the power
amplifier module while transmittingor operating the transmitter.
DO NOT SUBSTITUTE PARTS OR MODIFY THE EQUIPMENT
Because of the danger of introducingadditional hazards, do not install substitute or lower
voltage parts to the equipment. Return to your authorised distributor.
EXERCISE CAUTION AND CORRECT DISPOSAL OF RF POWER DEVICES Most
RF power transistors and some RF power hybrids contain Beryllium Oxide. Although they
are normally safe, if physically damaged toxic dust may be released. Consult your local
authority for correct disposal thereof. Such devices are not normally used in the MX920.
WARRANTY CONDITIONS & PRECAUTIONS
The following conditions are not covered by the warranty of the MX920. Please ensure that
the MX920 is not subject to;
1. Over voltage or Reverse Power Supply Voltage.
2. Operation in locations subject to abnormal environmental conditions such as extreme
temperatures or ingress of moisture or excessively dusty environments.
3. Operation of the MX920 Transmitter output into an open or short circuit or an incorrectly
terminated load. Although a level of VSWR protection is included, greater protection is
provided by the addition of a TX RF isolator.

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© SPECTRA ENGINEERING 2003 Revision 1.1.4
Technical Manual
Table of Contents
Table of Contents
1. General
Description........................................................................................... 1
1.1 Physical
Description.................................................................................. 2
1.1.1 Front Panel
.................................................................................. 3
1.2 Module Functional
Description ................................................................. 6
1.2.1 RF Module and Main Controller Assembly
................................. 6
1.2.2 Power Amplifier
Module.............................................................. 7
2. Installation and
Operation................................................................................ 8
2.1
Installation ................................................................................................. 8
2.2 Screw Head
Types..................................................................................... 8
2.3
Operation ................................................................................................... 9
2.3.1 Setting to
Work ............................................................................. 9
2.3.2
Adjustments ................................................................................ 11
3. Standard Features
........................................................................................... 12
3.1 Programmable Channel
Spacing ............................................................. 12
3.2 Programmable DCS / CTCSS encoder /
decoder .................................... 12
3.2.1
Description ................................................................................. 12
3.3 Local Speaker, Mic Socket and Front Panel Mute / Squelch Controls... 12
3.3.1
Description ................................................................................. 12
3.4 Local Channel Change
............................................................................ 12
3.4.1
Description ................................................................................. 12
4.
Options.............................................................................................................. 14
4.1 Simplex Changeover
Relay ..................................................................... 14
4.1.1
Description ................................................................................. 14
4.1.2 Installation
................................................................................. 14
4.2 U29 Balanced and Isolated VF plus E&MError!Bookmark not defined.
5. Technical
Description ...................................................................................... 16
5.1 Exciter Section
........................................................................................ 16
5.2 Receiver
Section...................................................................................... 16
5.2.1 General Radio Management
...................................................... 17
5.2.2
TX Signal Processing ................................................................. 18
5.2.3
RX Signal Processing ................................................................. 18
5.2.4
RF Power Control...................................................................... 19
5.2.5
User Interface............................................................................. 19
5.3 Powe
r A
mplifier Module......................................................................... 19
6. MX920 Base Station Fault Finding Procedure
............................................. 21
6.1 MX920 Base Station
............................................................................... 21
6.1.1 Transmitter Section
.................................................................... 21
6.1.2 Receiver
Section......................................................................... 22
6.2 Microcontroller Section of
PCB .............................................................. 23

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MX920 Base Station & Repeater
Technical Manual
6.3.1 VCO 23
6.3.2 RX Front End 23
6.3.3 IF Section 23
6.4 Excit r 24
6.4.1 VCO 24
6.4.2 RF 24
6.5 Powe
r
24
6.3 Receiver
Section...................................................................................... 23
e
7. Alignment and
Testing.................................................................................... 27
7.1 Transceiver Setup, Calibration and
Alignment ....................................... 27
7.1.1 Setting the Model Number and Serial
Number........................... 27
7.1.2 Setting the Configuration
Information ....................................... 27
7.1.3 Adding and Setting Channel
Alignments .................................... 27
7.1.4 Setting
CTCSS/DCS.................................................................... 28
7.1.5 Power
Calibration ...................................................................... 28
7.1.6 RSSI Calibration
........................................................................ 28
7.1.7 Temperature
Calibration............................................................ 29
7.1.8 TX Power
Adjustment ................................................................. 29
7.1.9 Peak Deviation and Modulation Balance
Alignment .................29
7.1.10 TX Centre Frequency
Alignment ................................................ 30
7.1.11 Microphone Line Input Level (Nominal Deviation Or Peak
Deviation
Mode)........................................................................ 31
7.1.12 Mute Threshold Setting
.............................................................. 31
8. Appendices
....................................................................................................... 32
8.1 MX920 Interface Connections
................................................................ 32
8.1.1 CN6 Simplex
Relay ..................................................................... 33
8.1.2 CN7 TX
Output ........................................................................... 33
8.2 MX920 Test
Points.................................................................................. 34
8.3 Establishing RS232
Communications ..................................................... 35
8.3.1 Software Menu
System................................................................ 36
8.3.2 Interfacing Information .............................................................. 37
8.4 MX920
Specifications ............................................................................. 37
8.4.1 Operating Frequency Bands
...................................................... 37
8.4.2
General ....................................................................................... 38
8.4.3 Transmit
..................................................................................... 39
8.4.4 Receive
....................................................................................... 40
8.4.5 Ancillaries
.................................................................................. 40
8.5 MX920 Model Number Configuration
Guide ......................................... 41

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Technical Manual
Table of Contents
List of Tables
Table 1-1 LED Functions ................................................................................................ 4
Table 1-2 Rear Panel
Connections.................................................................................. 5
Table 2-1 Micro Controller
Jumper.............................................................................. 10
Table 5-1 Microprocessor Port
Parameters.................................................................. 17
Table 7-1 Peak Deviation Settings
................................................................................ 29
Table 7-2 Nominal
Deviation ........................................................................................ 31
Table 8-1 MX920 Interface
Connectors........................................................................ 32
Table 8-2 MX920 Accessory Socket
Pinout................................................................... 32
Table 8-3 MX920 Test
Points......................................................................................... 34
Table 8-4 Rs232 Pin configuration
................................................................................ 35
Table 8-5 General
Specifications .................................................................................. 38
Table 8-6 Transmit
Specifications ................................................................................. 39
Table 8-7 Receive
Specifications ................................................................................... 40
Table 8-8 Ancilary
Specifications.................................................................................. 40
Table 8-9 MX920 frequencies
bands .............................................................................. 41

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MX920 Base Station & Repeater
Technical Manual
List of Figures
Figure 1-1 MX920 Horizontal andVvertical types of Front Panel LEDs......................... 3
Figure 1-2 MX920 Rear Panel with Power Supply and Duplexer
fitted. ........................ 5
Figure 7-1 Under (increase
level) ................................................................................. 30
Figure 7-2 Over (decrease
level)................................................................................... 30
Figure 7-3 Correctly Aligned
Waveform ....................................................................... 30
Figure 8-1 RJ45 socket viewed from front of
MX920.................................................... 33
Figure 8-2 Front veiw of DB9 female connector and RJ45 Modular male
connector ... 36
Figure 8-3 RS232
Cable ................................................................................................. 36

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© SPECTRA ENGINEERING 2003 Revision 1.1.4
Technical Manual
1. General Description
The MX920 series employs state of the art design and construction methods to
deliver
a
range of high performance, very reliable radio base stations and repeaters. They are
ideally suited for use in VHF or UHF two-way voice communications radio systems.
Fractional synthesizers’ and the two-point modulation method give the added
advantage of linear frequency and phase response from DC to 3 kHz for accurate
reproduction of voice and low frequency digital signalling systems. The Receiver and
Exciter circuits are contained in single special aluminium housing together with the
associated audio processing and digital control on a single circuit board. The Power
Amplifier is also contained in its own extruded aluminium housing and can be easily
removed from the main chassis. The MX920 also incorporates ‘Plug and Play’
technology and performs automatic self-calibration. A complete module changeover is
field replaceable in very short time.
The MX920 employs some unique features in its design and much thought and
consultation has been used to provide a product that offers an extreme degree of
flexibility for the installer and service person. For example, all options may be easily
field retrofitted at a later date. A common chassis is used for both vertical and
horizontal version models. Batteries may be installed at two or both locations in the
chassis. Internal wiring has been simplified and cut by 90%. In addition, servicing is
simplified with one single main PCB having all components on one side of the PCB.
This permits the Technician to diagnose problems while either still connected in the
chassis or powered simply and independently on the test bench.
The flexibility of the MX920 series allows it to be configured for a wide range of
applications without removing any covers.
Standard MX920 applications include:
♦ Conventional 2-Way voice base station
♦ Full duplex or simplex base station
♦ Voice repeater
♦ Point to point link
♦ Fast 25 mS multi hopped repeater
♦ Local operation
The MX920 incorporates special technical features, of which the key ones are listed
below:
♦ Extremely low conducted emissions
♦ Extremely low transmitter spurious
♦ Fast transmitter on time
♦ Transmitter frequency response down to DC
♦ Low group delay distortion
♦ Full sub band RF switching bandwidth
♦ No re-tune design for receiver and transmitter
♦ Fully software programmable

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MX920 Base Station & Repeater
Technical Manual
♦ Built in diagnostics
♦ Built in community multi-tone style repeater
♦ CTCSS, Full duplex DCS, 5 tone, local speaker and many other options included
as standard
♦ Programmable channel spacing
♦ Low receiver standby current consumption
♦ Flash upgradeable
In addition, the MX920 can be fitted with options, not being limited to the following:
♦ Simplex antenna changeover relay
♦ Power supply
♦ Duplexer
♦ Batteries for power backup system
♦ Horizontal or vertical standing
♦ Rack mount
♦ Wall mount kit
♦ Desk microphone
For further information see Section 4, additionally, please contact Spectra
Engineering.
Note: Not all options and features may be available at the time of order. Please also
refer to Spectra Engineering’s web site for software feature upgrades and additional
documentation as available. www.spectraeng.com.au
1.1 Physical Description
The MX920 is a compact fully self contained Base Station and Repeater. It is
designed to stand either horizontally or vertically on a desk or like. An optional 19"
3RU rack kit allows the standard horizontal version to sit on rack-mounted tray. The
depth of the unit is 330 mm and the weight is less than 9 kg without the power supply,
duplexer or battery fitted. With the addition of the Wall mount kit, the vertical MX920
can be mounted against a wall for convenience.
The unit consists of two main sub assemblies, the main RF assembly and a Power
Amplifier Module. These modules are housed in sturdy steel case.
An internal power supply may also be pre-installed or retrofitted at a later date. As it
is a fully self contained Power Supply, it may also be safely operated outside the
MX920 without any exposed mains voltage terminals.
The MX920 features a high degree of RFI and EMI screening throughout the design
and construction. The receiver and exciter RF circuits are contained in solid
aluminium enclosure. The PA module is contained in a special compact and efficient
extrusion for minimum harmonic radiation. This design results in low conducted and
radiated emissions and minimal susceptibility to RFI and EMI.
User interface is via the front panel microphone socket which includes a serial port for
software programming and upgrading.

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Technical Manual
Installation and Operation
1.1.1 Front Panel
1.1.1.1 Standard Front Panel
The MX920 front panel comes in both horizontal and vertical types, this can be see in
the illustrated below. The front panel provides the user with real time status of the
MX920.
Figure 1-1 MX920 Horizontal andVvertical types of Front Panel LEDs
♦ Microphone /Accessory Socket
An RJ45 socket is provided on the front panel for connection of a
microphone. This socket is wired for compatibly with other industry
standard microphones. The desk top microphone is compatible with the
MX920 and MX800. Also provides RS 232 Communication between radio
and PC. The pin configuration can be found in Appendices Section 8.1
♦ RS232 Port
The RS232 programming port is part of the front Panel Microphone
accessory socket. You will be required to make a RS232 cable to be able to
communicate will the in built menu system software in the MX920. Please
refer to Appendices Section 8.3 on how to make this cable.
♦ Loudspeaker and Volume Control
A 3 Watt loudspeaker is provided to monitor 'on air' received audio. The
volume is adjusted in the usual manner by Rotating the volume control
clockwise to adjust the volume control for a comfortable listening level. If
no sound is heard, temporarily un-mute the radio by briefly rotating the
Squelch Control full anti-clockwise. You can adjust the volume
by
listening to the receiver's background noise.
The speaker can also monitor a tone output function from the
microcontroller.This may be used in conjunction with the appropriate
software configuration to generate an alert tone to the user.
♦ Mute / Squelch Adjustment
The squelch is used to eliminate any annoying background noise when
there are no signals present. When no signal is received, rotate the Squelch
control (SQL) fully counter clockwise first, and then rotate SQL clockwise
to the point that the noise just disappears. This will provide optimum
Squelch performance.
When the Squelch is Open, the receiver's background noise can be heard
and
'Green RX LED' is lit on the front panel display. When the Squelch is
closed, the receiver remains quiet when there are no signals present but any
incoming signals will override the Squelch and be heard in the speaker.

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MX920 Base Station & Repeater
Technical Manual
When CTCSS is enabled the channel remains quiet until
someone transmits
using the same tone. Should the receiver be setup for the reception of a
signalling tone, the 'Green RX LED' lamp with be on,
also if it contains
the correct tone the 'Yellow Tone LED' lamp will be lit, and audio out of
the speaker will then be heard. When the transmission ends, the channel
becomes quiet again. By using different tones, several groups of people can
share the same channel without disturbing each other.
NOTE: If an incoming signal is very weak and is close to the minimum
squelch level, it may become broken or “chopped” by the squelch action.
To prevent this, simply open the squelch to allow the signal to be heard
clearly. Alternatively,you can reduce the squelch sensitivity as described
above to block out unintentional weak signals.
♦ Front panel Channel Change Control
Refer to Section 2.3.1.3 for channel select method.
Table 1-1 below explains the functions of the front panel LED's. Each LED indicates
the status of the MX920 in real time. As the LEDs are also software programmable, it
is also best to check the settings in software.
LED COLOR FUNCTION
POWER BLUE Indicates the power supply voltage is within
limits. A flashing display indicates that
battery operation is current. No display
indicates the voltage is not normal.
RX AQUA A signal is being received by the receiver or
the receivers squelch is open.
TX RED The transmitter is transmitting RF power.
TONE YELLOW A valid Continuous Tone Coded Squelch
Signal (CTCSS) or Digital Coded Squelch
(DCS) or 5 Tone signal has been detected.
ALARM ORANGE A prearranged alarm condition exists.
REPEATER GREEN The local repeater mode has been activated
Table 1-1 LED
Functions
Switch FUNCTION
REPEATER Selects local Repeater mode
ACCESSORY Software programmable
Table 1-2 Switch
Functions

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© SPECTRA ENGINEERING 2003 Revision 1.1.4
Technical Manual
Installation and Operation
1.1.1.2 Rear Panel
The rear panel image shown has the internal Power supply fitted, alternatively the
MX920 can be ordered without the Power Supply or it can be retrofitted at a later date
should this be required. In the case of power being fed externally, the flying lead
is
then
routed out through the cable clamp grommet supplied with all units. No change
to the wiring in this case is required.
The MX920 also has the provision to mount two Sealed Lead Acid Six (6) Volt
Batteries (to be connected in series) in place of the Duplexer using the Battery mount
option. Alternativelyanother set of batteries can be also mounted in place of the
Power Supply Module. Hence a degree of power supply solutions can easily be
accommodated for special applications like a portable Repeater. Wiring for these
special cases must be performed by the appropriate qualified personal. Please contact
your Dealer or Distributor should you require the appropriate assistance.
Conn Type Function Description
Flying Lead DC Power input 13.8 Volt DC power input.
N TYPE
(CN6) Simplex relay out or N type RX input Location for internal simplex relay. The antenna for RX / TX connects to this point.
Alternatively an N-Type connector can be
used for the input to the receiver for full
duplex operation.
N TYPE
(CN8) TX output The RF power output from the transmitter for full duplex operation.
Table 1-2 Rear Panel
Connections
Figure 1-2 MX920 Rear Panel with Power Supply and Duplexer
fitted.
(RF Connecting cables not
shown)

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MX920 Base Station & Repeater
Technical Manual
1.2 Module Functional Description
1.2.1 RF Module and Main Controller Assembly
The MX920 consists of a full duplex RF module with its own shielded metal housing
and a Main Controller board integrated on a single PCB. Using advanced yet
simplified circuit designs, the size and complexity is reduced. This affords a number
of advantages including;
♦ Cost reduction
♦ Reduced number of components improves reliability and MTBF
♦ Consistent and improved manufacture
♦ Elimination of connectors and cabling
♦ Reduction of human error
♦ Faster maintenance or swap out
The Exciter module generates the low level, on frequency, RF transmitter signal
which is later amplified to nominal output power level by the Power Amplifier
module. The exciter consists of a Voltage Controlled Oscillator (VCO) and associated
main RF board, which, in conjunction with the reference oscillator and the PLL
circuitry, forms a two-point modulation programmable frequency synthesiser.
Frequency programming data is received from the Micro Controller via an 3 wire
serial data bus.
The exciter circuitry features a modulation bandwidth from DC for accurate CTCSS
and DCS generation and a wide RF switching bandwidth which covers the entire sub-
band. The average maximum RF output power is > +24.7 dBm / 300 mW. Normally
no adjustments are required, however should the carrier freq need re-alignment for
future maintenance, the TCXO reference oscillator frequency can be adjusted
manually or electronicallyadjusted via software settings.
The fractional N synthesiser provides ultra low spurii while still maintaining fast lock
times. The frequency step size is auto determined at 5.0 kHz or 6.25 kHz.
The receiver section accepts the low level RF input signal and amplifies, filters and
conditions the signal prior to detecting the wanted audio component. The Receiver
features the same advanced synthesiser and wide bandwidth as the exciter. The front
end bandpass filter uses very high tolerance components to minimise production
spread variations has a wide bandwidth and eliminates the need for future alignments.
The bandwidth is equal to the band allocation (refer to Section 8.5 for details of the
band allocations). The VCO has low phase noise and covers the full sub-band.
The receiver has high sensitivity while maintaining excellent intermodulation
immunity and adjacent channel rejection. A dual first IF filter provides excellent
rejection to common known spurious responses. High blocking of over 100 dB typical
ensures that strong interfering signals do not desensitise the receiver when receiving
weak signals.
The Micro Controller section is physically located towards the centre on the main
board and controls all signal connections (apart from the RF connections). It controls
the operation of the RF sections and acts as the interface between the user controls,
indicators and the RF sub sections. Together with the VF ASIC chip, processed
transmit and received audio is passed to and from the Exciter and Receiver sections as
well as providing all other audio signalling functions of the transceiver.

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© SPECTRA ENGINEERING 2003 Revision 1.1.4
Technical Manual
Installation and Operation
An on onboard EEPROM stores all of the user channel related data such as
frequencies, CTCSS tones etc. A serial port at the Microphone accessory socket of the
MX920 provides access to the Controller card software configurations for the purpose
of the user to create and change this channel related information.
Special functions capable of being carried out include non-predictive full duplex
CTCSS encoding/decoding, DCS encoding/decoding as well as 5-Tone and DTMF
signalling. Digipots under the control of the processor ensure that user set up levels
for TX deviation and power levels are correctly set for each channel.
1.2.2 Power Amplifier Module
The PA receives the low level modulated RF signal from the Exciter RF output and
amplifies and filters it to final output power level. Forward and reflected power
voltages are fed to the Micro Controller.
The PA is very compact and efficient for high reliability and low cost. The heatsink
has minimal temperature rise even under continuous operation, ensuring the best
MTBF obtainable for a practical design. A low loss 13 element elliptical low pass
filter ensures that harmonics remain below –90 dBc. The new PA module uses the
latest LDMOS technology and using only two active RF transistors improves
efficiency and increases the operating bandwidth. At the same time this reduces the
number of components used and further improves the long term reliability.

2003 Revision
MX920 Base Station & Repeater
Technical Manual
2. Installation and Operation
2.1 Installation
MX920 series radios are securely packed for transport with special packers within a
cardboard container. Before unpacking the MX920 radio, please inspect the packaging
for signs of damage and report any damage to your MX920 distributor.
Upon unpacking of the MX920 radio, please ensure that all items shipped were
received, report any missing items to your MX920 distributor.
Check the fan is free or does not look blocked as operation of the radio will be
affected if any packaging or shipping damage causes the fan to stop working.
If you intend to install the radio in an equipment rack consult the suppliers
instructions for your system. If the radio is to be used in a stand-alone configuration,
ensure that it is in a secure, dry location with sufficient air space around it to allow for
adequate ventilation. It is recommended that the chassis is earthed to the equipment
rack.
Equipment connection details are located in Appendix 8.1. The MX920 will draw
approximately 7 to 9A (band dependent) for 50 Watts on transmit and the gauge of the
DC cable fitted to the 12V supply connector should be adequate to ensure less than
0.5V volt drop at this current.
2.2 Screw Head Types
Modern screws employ a wide variety of drive designs, each requiring a different kind
of tools to drive in or extract them. Spectra Engineering has chosen the Pozidriv ®
screw head and screwdriver as it preferred screw type on all of its products, sizes 1 &
2. This is because the Pozidriv system is the choice for high volume assembly
operations. It provides self-centring system and excellent driving control with less
operator fatigue.
It is similar to the classic Phillips cross-head. The differences lie in the way that the
heads are machined. The Phillips head has 4 simple slots cut out of it, whereas in the
case of the Pozidriv each slot is the result of two machining processes at right angles.
The result of this is that the arms of the cross are parallel sided in the case of Pozidriv,
and tapered in the case of Phillips. The Pozidriv has four additional points of contact,
and does not have the rounded corners that the Phillips screw drive has.
Phillips screwdrivers will usually work in Pozidriv screws, but Phillips screwdrivers
are likely to slip or tear out the screw head when used in Pozidriv screws. It is
important that you use the correct type and size screwdriver to avoid damaging the
screw head.
Pozidriv Philliips
Exrta contact points
Figure 1-1 Top view of screw heads

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© SPECTRA ENGINEERING 2003 Revision 1.1.4
Technical Manual
Installation and Operation
Parallel sides Tapered sides
Figure 1-2 Side View of screw Heads
Used on All
Spectra products
Exrta contact ridges
Don’t used this type
on Spectra products
Pozidriv Phillips
Parrallel driving
flute
Tapered driving
flute
Figure 1-3 Screw driver Tip View
2.3 Operation
The MX920 can operate in local control Base Station mode or Repeater mode via the
front panel controls. Setting up the MX920 to operate in the wanted settings is
straightforward and involves one main step.
•Using a PC or handheld serial computer running standard communications
terminal software, connect the device RS232 serial port to the Microphone
Accessory socket at the front panel of the MX920. Set the appropriate parameters
as required. See section 8.3 for establishingRS232 Communications.
Note: All MX920s’ are set up with a standard default configuration. Test frequency
are stored within the MX920 as supplied from Spectra’s factory, however these are
not normally accessible and each station is supplied with no test channel .
2.3.1 Setting to Work
The following sections describe the steps necessary to set the MX920 to operate as
required.

2003 Revision
MX920 Base Station & Repeater
Technical Manual
2.3.1.1 Micro Controller Jumper
There is only one jumper and it is used for selecting the microcontroller operation
mode. The user will not normally have to change the position of this jumper as it is
only used in the initial factory setup.
Table 2-1 below summarises the functions of the jumper.
JMP Function / Description Default
Selection Default Position
JMP 1 /
CNVSS Selects either default single chip
mode or microprocessor mode for
the microcontroller.
Single chip
mode ON
Table 2-1 Micro Controller Jumper
2.3.1.2 Select Operating Mode
The MX920 can operate in a number of different modes. The primary alternatives are
full duplex, which is the default mode, repeater and simplex. Using the built-in radio
configuration menu system, the operating mode is programmed for each channel.
When a channel is selected in operation, the MX920 adopts the mode programmed for
that channel. Repeater mode is easily selected from the front panel by depressing the
Repeater button. The front panel repeater button can also be lockout in software, to
prevent accidental turn off.
2.3.1.3 Select Operating Channel
The MX920 has a channel capacity of 255. The RF and CTCSS frequencies for each
channel are programmed using the radio configuration menu system channel edit
screen. There are two ways of selecting the operating channel.
1. Software channel select. If the front panel push-wheel switch is set to 00 then it is
possible to send a software command to the radio to select the channel.
In
addition,
channel number 00 may point to another channel number in the channel
list, thus effectively providing 100 channels from the front panel channel
selector.
2. Front panel Push-wheel switches. The channel select port is internally wired to
the Push-wheel switches, the desired channel is simply dialled up on the
switches. The 99/100 channels are selectable on the front panel. This channel
selector has the added advantage of displaying the current channel even when the
power is turned off.
The following rules apply.
♦ The front panel push-wheel switches have priority. If push-wheel switches SW1
are not set to 00, the software command will be ignored.
The exact functionality and available features will also depend upon the firmware
version installed.
2.3.1.4 Configure Alert / Alarm LED
The MX920 has an LED to display the status of alarms. The alarm trigger conditions
can be set using the built-in radio configuration menu system software. The ALERT
LED an be set to trigger on low forward power, high reflected power, power supply