MRT AU10 Development - Case Study

RadioCAD Limited have a long and successful working relationship with Marine Rescue Technology (MRT), having developed MRT’s current range of beacons, receivers and direction finders.

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Following MRT’s acquisition by Mobilarm of Australia, RadioCAD won the contract to develop MRT’s new dual-band Man Over-Board (MOB) emergency beacon, the AU10.

The requirement was to take MRT’s market leading AU9 121.5 MHz Alerting Unit (AU), and add Maritime AIS position indicating technology. This meant designing a dual-band product because 121.5 MHz is an AM locating channel in the aircraft VHF band, whereas AIS uses two FM channels in the maritime VHF band.

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The AU9 PCB footprint wasn’t allowed to change because of MRT’s considerable investment in approvals for the AU9 enclosure. This meant cramming twice as much circuitry into the same space and therefore a component geometry shrink. Additionally a GPS antenna had to be added to AU9’s VHF antenna in the existing LED indicator bulb. The bulb is at the other end of AU9’s coaxial antenna feed. It couldn’t be located in the electronics housing as this unit spends most of its time underwater. RadioCAD had to design circuitry to multiplex four signals onto a single coax at both ends:

(i) VHF transmission @ 100 mW with very low loss
(ii) GPS received signal @ 150 dB quieter than the VHF signal
(iii) LED visual signalling (bright flashing red and green)
(iv) Power to the GPS Low-Noise Amplifier (LNA)

RadioCAD designed custom diplexers in the antenna bulb and AU10 motherboard achieved the required signal separation.

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AU10’s fully synthesised dual-band AM/FM VHF synthesiser was a completely new design. The demanding approvals requirements for AIS, combined with opposite but equally demanding requirements for 121.5 MHz and the small space requirement, made the project technically very difficult. RadioCAD’s first attempt was unsuccessful. Although it did result in a proof-of-concept prototype that basically worked, the design would never pass the necessary approvals requirements.

RadioCAD had to go back to the drawing board and completely re-design the synthesiser from scratch. Only the dual-band RF Power Amplifier (PA) could be saved from the initial design. Although this delayed completion of the project, the re-design was undertaken at no additional cost to MRT.

The second prototype worked extremely well and became the basis of the final product. First prototypes were delivered in October 2012 and the initial pre-production run completed and evaluated by January 2013. RadioCAD completed European RTTE approvals in April 2013.

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Presently RadioCAD are working with MRT on AU10 production control, US approvals, and Helicopter Transit approvals.