MX921 Low Current Repeater

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MX921 Product Information


The MX921, low current Repeater and Base Station solution, is designed from the ground up for the absolute lowest power consumption and features the lowest current draw of any professional high performance Repeater/Base Station. Product offerings today reduce power wastage by constantly duty cycling (time slice, sleep mode) the receiver on and off. This has no advantage when the receiver is receiving and only serves to significantly slow the response of the receiver carrier detection time and resultant Repeater wake-up time. Other alternatives degrade the RF performance to unacceptable levels. The MX921 does not sacrifice any of these critical requirements and in fact still achieves a level of performance few competitors can provide at any power consumption level.

A few relevant specifications below will illustrate the point.

Even if your application is not Solar powered, the MX921 can deliver the high performance and advanced features you need in today’s congested Radio Spectrum.

An optional internal Solar Regulator and intelligent Battery Manager inside the MX921 makes it the stand out choice for remote sites.


This document is also available in PDF Format.

Minimum performance to exceed the following for 148MHz to 520MHz*:

  • AS4295-1995,
  • R&TTE EC Directive 1995/05/EC
  • EN300 086 –1,2 (2001- 03),
  • EN 300 113, EN 301 489 – 1,5 (2002 – 08)
  • EN 60950 (2000)
  • RFS25, RFS26, RFS32,
  • TIA/EIA-603,
  • BAPT 225 ZV 1/2098 (German soft keying),
  • FCC Part 22, 74, 90, 90.210, 80.475,
  • MIL-STD-810E (Parts thereof),
  • RSS119 Issue 6

* Conforms but not all approved.


  • FCC: OKRMX920
  • CE/R&TTE: CE1313!
  • IC: 50605A
  • AUST: AS4295


Frequency Range: Coverage 148-520 MHz.

Band Frequency Range
Band D3 148-174 MHz
Band N2 400-435 MHz
Band O2 435-470 MHz
Band P2 450-485 MHz
Band Q 485-520 MHz

Synthesis Method Non-mixing PLL.
Fractional N synthesizer.
Modulation Direct FM two-point method.
Channel Spacing Programmable 25kHz / 12.5 kHz
Synthesizer Step Size 6.25kHz or 5kHz auto select
Channels 99 front panel selectable,
255 PC software selectable
Supply Voltage 13.8 +/- 20%
Operating Temperature -30 to +60C
Physical Size 2RU Case, 325mm deep including fan
Standard LED indicators Power, RX, TX, Tone, Alert, Repeater.
Standard Switches Two press button type.
Standard Controls Volume knob, Squelch screwdriver adjust.
Interface Front panel Microphone accessory socket, speaker,
rear connector DB25. Location for DB9 x 2, DB15, RJ45.
Weight 8kg



Standby <60mA receive, typical 55mA.
Receiving <60mA receive, typical 57mA.
Receiving and *2Watt TX RF output <850mA (1Watt PA module)
Receiving and 25Watt TX RF output <5.5A, typical 4.9A.
Receiving and 50Watt TX RF output <10A, typical 7.8A.
* 2W RF Output, not guaranteed when using 1W PA module.




Transmitter Feature
RF Power Output 1W to 50W or
0.1 to 2W* UHF PA opt (1W nominal)
Frequency Stability >300MHz
< 300MHz
–10 to 60C for 1.5PPM, –30 to -10C for 2.5PPM
–10 to 60C for 2.5PPM, –30 to -10C for 5PPM
Audio Response Flat within +1,-3dB across BW
Audio Bandwidth 300Hz to 3000Hz
Modulation Distortion Less than 3% @ 60% deviation
S/N Ratio Better than 50dB, (WB).
Better than 44dB, (NB).
Conducted Spurious Emissions Better than -90dBc
Conducted Harmonic Emissions Better than -90dBc
RF Switching Bandwidth Full Sub band
RF Switching Bandwidth PA Full Sub band
Duty Cycle 100% for 50W RF output
RF Rise Time <50mS with VCO in cold standby
* 2W RF Output, not guaranteed when using 1W PA module.




Receiver Feature
Sensitivity Better than -120dBm for 12dB SINAD.
Typical -123dBm
Selectivity 135-520MHz More than 85dB for 25kHz adj channel.
Typical 90dB
more than 75dB for 12.5kHz adj channel.
Audio Bandwidth 300Hz to 3000Hz (+1,-3dB)
Image Freq Rejection Better than 100dB
Spurious Response Immunity Better than 85dB.
Intermodulation Immunity Better than 82dB.
Typical 84dB
Blocking Better than 100dB at +/- 1MHz point
Distortion Less than 3% @ 60% deviation
Frequency Stability –10 to 60C for 1.5PPM,
–30 to -10C for 2.5PPM
S/N Ratio Better than 50dB (WB).
Better than 44dB (NB).
Co-Channel Rejection Better than 5dB
RF Switching Bandwidth Equal to Sub band allocation
Receiver Front End BW Equal to Sub band allocation
Receiver Audio Power 1 Watt.



  • Very Low current consumption
  • No need for receiver duty cycling
  • System Interface
  • Fully Programmable / Configurable via PC or serial device
  • System independent, no additional software program required
  • High Speed CTCSS, Full Duplex DCS/DPL
  • Remote controllable Multi tone CTCSS community decoder
  • 100% full power duty cycle
  • 5 Tone signaling
  • High Accuracy Real Time Clock.
  • Multi staged TX VF processing with triple limiters
  • Flash Firmware Upgrade Capable
  • Battery backup system option
  • Built In Test Equipment (B.I.T.E.) and remote diagnostics
  • Broad Band High Efficiency LDMOS PA module
  • RX & TX Switching BW covers full sub band
  • Fast Serial Data Interface
  • Full Digital alignment and calibration
  • Field interchangeable PA module needs no re-alignment
  • Pre calibrated power and deviation alignment. Digital value
  • Low RFI and EMI emission design
  • Controlled TX RF envelope
  • DTMF decoder
  • DTMF Remote control
  • Latest technology, full SMD
  • Advanced and optimized RF design
  • High performance 16 bit Flash processor
  • Programmable 12.5/25kHz channel spacing
  • Configurable Function Front Panel LEDs
  • Low current LEDs with digital intensity control
  • Simple and fast disassembly for service
  • Precision internal shielding system
  • Minimal technician adjustments for future maintenance
  • Design spec –40 to 70 degrees C
  • Low aging oscillators
  • Universal microphone input circuit
  • Minimal interconnections
  • Options cans be easily retrofitted
  • Minimal mechanical adjustments
  • Front end RX filter never needs realignment
  • Built in TX modulation alignment audio oscillator
  • Built in auto alignment software guides technician
  • Fast and simple disassembly
  • Built on proven technology
  • Configuration password protected
  • Virtual elimination of internal wiring
  • Elimination of helical filters, quadrature coils, MCF matching and trim potentiometers


  • Desk Mic
  • Internal Simplex relay
  • Virtual PC Console including ANI / CTCSS / DCS / 5TONE / DTMF display (future proposed)
  • Solar panel and battery power management system option board.
  • Universal system interface



  • Not all items and features initially available.
  • Future software releases and features can be Flash Memory upgraded.
  • Due to ongoing development we reserve the right to alter specifications without notice.


Reliable Radio Communications. When You Need It Most.                        2013 Spectra Engineering Pty Ltd