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2003  Revision 

 

MX920 Base Station & Repeater 

Technical Manual 

 

 

 

 

8.  Appendices

 

 

 

8.1  MX920 Interface Connections

 

 

The user connections to the MX920 are all made via the Front and rear panel where 
the following connectors are located. 

 

 

 

No

 

Conn Type

 

Function

 

Description

 

CN6 

N TYPE 

Simplex relay out or 
N type RX input 

Location for internal simplex relay. The 
antenna for RX / TX connects to this 
point. Alternatively a N-Type 
connector can be used for the input to 
the receiver for full duplex operation 

CN7 

N TYPE 

TX output 

The RF power output from the 
transmitter for full duplex operation. 

SKL 

RJ45 

Microphone Socket 
and RS232 
Communication 

The socket provides a connection for a 
microphone. Also provides RS 232 
Communication between radio and PC 

 

See Table 8-2 

 

Table 8-1  MX920 Interface Connectors

 

 

Pin No

 

Function

 

Comment

 

1 

Low level muted RX VF 

600ohm Z, filtered and De-emphasis. 

 

Line level 

≈ 

-16dbm 

2 

+8V DC 

Current limited. 

3 

Microphone PTT 

Pulled to +5V via 10k resistor. Connect 
to ground for PTT. 

4 

Microphone VF 

600 ohms Z, gain and compression 
functions are software controlled. 

 

Desk Mic 

≈ 

-43dbm 

Compression enable.

 

 

Fist Mic 

≈ 

-23dbm 

Compression enable.

 

5 

EARTH common 

Pin 5 DB9M (PC RS-232). 

6 

Hook / Monitor switch 

For quiet base use. Connect to ground 
for quiet base operation. 

7 

RS-232 RxD 

Pin 2 DB9F (PC RS-232). 

8 

RS-232 TxD 

Pin 3 DB9F (PC RS-232). 

 

Table 8-2  MX920 Accessory Socket Pinout

 

 

The RJ45 pins are numbered as shown in Figure 3-4 below. 

Summary of Contents for BK RADIO SDMX920

Page 1: ...Base Station and Repeater SMX920 SDMX920 VER 1 1 4 0300 30973 700_REV 07 14 ...

Page 2: ......

Page 3: ...cument 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...

Page 4: ...MX920 Base Station Repeater Technical Manual 4 SPECTRA ENGINEERING 2003 Revision 1 1 4 This page left blank intentionally ...

Page 5: ...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 Cali...

Page 6: ... 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 transmitting or operating the transmitter DO NOT SUBSTITUTE PARTS OR MODIFY THE EQUIPMENT Because of the danger of introducing additional hazards do not install substitute or lower voltag...

Page 7: ... 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 ...

Page 8: ...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 MX...

Page 9: ...rt 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 fr...

Page 10: ...ront 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 ...

Page 11: ...een 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 s...

Page 12: ...y 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 assemb...

Page 13: ...er 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...

Page 14: ... 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 voltag...

Page 15: ...es 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 Po...

Page 16: ...or frequency can be adjusted manually or electronically adjusted 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...

Page 17: ...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 temperatur...

Page 18: ...nnector 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 choic...

Page 19: ...nted 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 establishing RS232 Communications Note All MX920s are set up with a standard default...

Page 20: ...acity 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 c...

Page 21: ...Front Panel Accessory Button can be software configured to perform a number of functions such as tone encoder call cancel function for tone decoder and alarm clear Please refer to the radio configuration menu system for additional setup information The exact functionality and available features will also depend upon the firmware version installed 2 3 2 Adjustments The MX920 has adjustable paramete...

Page 22: ...d any valid CTCSS tone to be decoded Any standard TX CTCSS tone may be associated with the programmed decode tone through the channel edit screen in the radio configuration menu system Multiple CTCSS tones are programmable for any channel providing Community Repeater functionality The DCS encoding function provides continuous repetitive digital word modulation to the transmitter The decode functio...

Page 23: ...ernative channel select methods MX920 Testing 1 Connect a Communications Cable to the MX920 2 Set MX920 into Diagnostics mode using the built in radio configuration menu system The MX920 will periodically update the terminal screen with the selected channel the power supply voltage and various other diagnostic information 3 Change the channel on the local channel switches and check that the channe...

Page 24: ...een of the built in radio configuration menu system When the simplex mode is selected a small time delay is added to the transmitter RF to allow the relay to changeover and set the simplex operating mode respectively 4 1 2 Installation Components Required 1 Coaxial Relay Assy complete with TX and RX cable connected Qty 1 2 2 of M3 Metric 8mm pozi drive screws Qty 2 Test Equipment Required 1 Commun...

Page 25: ... Set the test set to measure Rx line level and ensure that the Receiver is operating correctly 4 Set the test set to measure TX modulation level and Inject into RJ45 pin 4 with a audio generator output level of 10dBm 5 PTT the MX920 RJ45 Pin 3 and measure the TX Power and modulation depth Ensure that the coaxial relay operates correctly and that the full RF power is measured on the test set 6 Oper...

Page 26: ... are the similar for the exciter and receiver sections The VCO consists of a common gate FET LC tank circuit The power supply to the VCO uses an 8 volt regulator and active filter for maximum noise rejection For standard modulation transmit audio is fed to the conventional point of the VCO varactor For 2 point modulation audio is also fed to the voltage control pin of the VC TXCO this in effect ca...

Page 27: ...e Micro Controller section accommodates an M30620FCAFP microprocessor IC2 a 16 kbyte EEPROM IC1 as well as I O latches and other miscellaneous circuitry The Micro Controller is responsible for ensuring that the radio acts as programmed by the user It stores the user entered parameters for each channel in EEPROM This information includes RX and TX RF frequencies RX and TX CTCSS frequencies as well ...

Page 28: ... screen The MX920 uses the technique of calibrating all Transmit Modulation level alignments in the Wide Band mode 25kHz channel spacing for maximum accuracy Gain setting resistor arrays switched under control by the microprocessor automatically scale the levels so as to set the correct modulation depth as required for Narrow Band channels 5 2 3 RX Signal Processing Raw Discriminator audio to the ...

Page 29: ...Controller board Output latch IC4 drives the six LED indicators on the front panel The function is described in Section 1 1 1 An input port on IC2 serves to accept the programmed status of the 8 bit BCD channel select input from the front panel Pushwheel switches IC31 is a 3 Watt speaker amplifier which drives the internal speaker Microphone audio is into the front panel RJ45 connector In addition...

Page 30: ...n lines fabricated on the PCB artwork The sampled RF energy is rectified to provide a proportional DC voltage output The PTT signal enables the amplifier circuit by providing bias to the transistors A thermistor TSI physically located on the PA heatsink monitors the heatsink s temperature and is monitored by the Micro Controller ...

Page 31: ... 2 Using the in built menu system check that the frequency tables and configuration settings are correct 6 1 1 Transmitter Section Connect the output of the Power Amplifier Module to a Comms test set or a RF power meter Using in built menu system select Diagnostics check the TXVCO locking voltage is between 2 14 V and there is no TXVCO Unlock alarm displayed If the locking voltage is out of spec o...

Page 32: ... If the audio deviation is incorrect then go to the Transmitter alignment procedure If there is no audio modulation then check the audio level on pin 7 IC25B TP22 on the Microcontroller PCB If there is no audio on the above test point then go to section 6 2 else go to section 6 4 6 1 2 Receiver Section Using in built menu system selected Diagnostics check the RXVCO locking voltage is between 2 14 ...

Page 33: ...ll the above tests didn t pass then the VCO or IC9 may be faulty Return the to your Service Centre 6 3 2 RX Front End Solder a 2 way Berg header onto a flying coax lead Remove cut link I near the mixer M1 and then fit solder link J Inject a RF signal into CN5 Check the sensitivity is better than 105 dBm If the sensitivity is OK past this point then check that the supply voltage TP4 to the collecto...

Page 34: ...ystem increase the Transmit Power control to maximum and check that the output power is greater than 24 dBm To insure power control is at max Short C208 together located under SKB If the Exciter power is low check for the 8 V supply voltage at the outputs of TR27 and TR16 Lift one side of C216 which leads to R128 and solder a flying lead to that end of the capacitor check the output power of the V...

Page 35: ...eed 24 dBm whilst measuring the output power output 50watts 25dBM If output power is low then turn the supply voltage OFF and lift one side of the capacitors connecting to the directional coupler and solder a flying lead to the lifted side Connect the earth of the flying lead to the earth of the PA Turn ON the supply voltage and the signal generator RF output PTT the PA and increase the generator ...

Page 36: ...2003 Revision MX920 Base Station Repeater Technical Manual This page left blank intentionally ...

Page 37: ...usly setup and the user intends to recalibrate and align the radio then steps 7 1 1 7 1 2 and 7 1 3 can be ignored as the model number serial number configuration and channel information will have already been loaded Using a PC or handheld serial computer running standard communications terminal software connect the device RS232 serial port to the RJ45 Accessory socket at the front panel of the MX...

Page 38: ...equencies or DCS codes programmed into the alignment channel as the subtone levels will give a false indication of the peak deviation levels The MX920 contains circuitry that automatically scales the deviation so the nominal deviation is not exceeded when a sub tone is transmitted 7 1 5 Power Calibration DO NOT USE THIS PROCEDURE TO SET THE TX OUTPUT POWER REFER 7 1 8 TX POWER ADJUSTMENT TO DO THI...

Page 39: ...basis The alignment is done using the Alignment Screen in the built menu system To carry out this procedure the demodulated output of the transmitter output needs to be connected to a CRO or some other piece of equipment giving a visual display of the demodulated output IF Bandwidth of the RF test set should be set at 20kHz or greater 230kHz on the HP 8920 and de emphasise should be off The audio ...

Page 40: ...ck the deviation alignment as the reference oscillator alignment affects the deviation This may require running through the deviation alignment again after the oscillator alignment procedure 7 1 10 TX Centre Frequency Alignment The reference oscillator alignment is used to set the correct centre frequency for each channel This is done on a per channel basis Oscillator alignment is done using a dig...

Page 41: ...adio also can operate in a peak deviation mode To change mode use the built in menu system Configuration Menu Software Switch Configuration Menu Nominal Peak deviation 7 1 12 Mute Threshold Setting Test Equipment PC with Terminal software RF Communications test set 13 8VDC power supply MX920 Testing Rx Mute 1 Monitor the low level muted RX VF pin1 of RJ45 with RF Communications test set Inject the...

Page 42: ... RS232 Communication The socket provides a connection for a microphone Also provides RS 232 Communication between radio and PC See Table 8 2 Table 8 1 MX920 Interface Connectors Pin No Function Comment 1 Low level muted RX VF 600ohm Z filtered and De emphasis Line level 16dbm 2 8V DC Current limited 3 Microphone PTT Pulled to 5V via 10k resistor Connect to ground for PTT 4 Microphone VF 600 ohms Z...

Page 43: ... also pre installed or retrofitted at a later date The N type connector for the RX port is removed and the relay is mounted in it s position which then acts as the RF I O port for simplex operation When this option is installed the radio programming will required to be change to reflect the simplex mode 8 1 2 CN7 TX Output This is an N type connector used as the TX RF power output ...

Page 44: ...er RF power 10 RSSI Volts 0 5V 11 Rx Enable 5V Rx Enable 12 PA PTT 0V PA PTT Enable 13 Rx Lock Detect 5V RX PLL Is In Lock 14 Rx VCO Volts 0 3 2 15V Voltage Depends On Frequency 15 Rx STB 0V Idle State 5V When Strobe 16 Tx Lock Detect 5V TX PLL Is In Lock 17 Mute Control Pin To IC1 P81 0V Mute Open 18 PA Temp Volts 19 PTT 5V PTT Enable 20 Tx VCO Volts 0 3 2 15V Voltage Depends On Frequency 21 Tx E...

Page 45: ...9 or DB25 Female connector with back shell 2 Metres of Flat phone cable or another RS232 complaint cable 8P8C RJ45 male modular connector 8P8C modular crimping tool 1 x Pair of side cutters Soldering iron and 60 40 solder Multimeter 13 8V DC power supply Fitting the 8P8C RJ45 Male Modular connector 1 Cut and strip Cable end to suit the 8P8C RJ45 male modular connector using modular crimping tool 2...

Page 46: ...ve Firmware Ver 0 2 0 and above Carriage return is required after typing RMENU The user will then be presented with a menu system from which various settings and configurations can be selected To exit the menu system the ESC key can be pressed Due to ongoing development please refer to www spectraeng com au for updates on firmware revision Getting started with Hyper Terminal 1 On the File menu cli...

Page 47: ... noise for RS232 cable maybe induced onto the audio cable Figure 1 1 8P8C RJ45 Modular double adaptor 8 4 MX920 Specifications Minimum performance to exceed the following for 30 MHz to 960 MHz AS4295 1995 ETS 300 086 Jan 1991 ETS 300 113 FCC Part 90 TIA EIA 603 BAPT 225 ZV 1 2098 German Soft keying CEPT T R 24 01 E Sept 1988 EC Marking EC EMC Directive 89 336 EEC RFS25 RFS26 RFS32 Conforms but may...

Page 48: ...60 C Individual Module Dimensions Main board W 260 L 227 H 35mm PA W 78 L 300 H 60mm Standard LED indicators Power TX RX Tone Alert Repeater Speaker output 3 Watt Frequency Range Coverage 148 520 MHz Synthesis Method Non mixing PLL Fractional N synthesiser Modulation Direct FM two point method 2 5 kHz narrow band 5 kHz wide band Channel Spacing 25 kHz or 12 5 kHz software selectable Synthesiser St...

Page 49: ...o 10C Audio response Flat within 1 3 dB across bandwidth Audio Bandwidth VF input 300 Hz to 3000 Hz Bessel LPF Modulation Distortion Less than 3 at 60 deviation S N Ratio Better than 46 dB wide band Better than 42 dB narrow Band Spurii Better than 90 dBc RF Switching Bandwidth Exciter Full sub band RF Switching Bandwidth PA Full sub band Duty Cycle 100 for 50W RF output with thermally controlled f...

Page 50: ...an 46 dB wide band Better than 42 dB narrow band Receiver Front End BW Equal to band allocation Audio Bandwidth VF output 300 Hz to 3000 Hz 1 3 dB Receiver Audio Power 3 Watts nominal 5 Watts peak Squelch Opening Time Less than 20mS 20dB SINAD Squelch Closing Time Less than 100mS Conducted Spurious Less than 57dBm Table 8 7 Receive Specifications 8 4 5 Ancillaries Parameter Specification TX Timer ...

Page 51: ... below shows how the model number is derived from the wanted options Consult Spectra for availability details on specific configurations and options SMX92 Band Frequency D3 148 174 MHz N2 400 435 MHz O2 425 460 MHz P2 450 485 MHz Q 485 520 MHz Table 8 9 SMX920 and SDMX920 frequencies bands 0 SMX SDMX920 SDMX92 OR Tx Rx Freq Band Refer to Table 8 9 Configuration R 50W Repeater B 50W Base 2 2W Repea...

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