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A high-power avionics test system is delivered from obsolescence

18 October 2015

Link Microtek has recreated an obsolete test system for a prime contractor in the defence industry to enable the end customer to continue critical support for an avionics EW (electronic warfare) system.

With its expertise in microwave engineering, electronics and mechanical design, Link Microtek was able to reproduce the complex unit working only from a set of old drawings and some parts. The unit was originally designed over 25 years ago, and no other specifications or technical details were available.

“As is often the case when dealing with obsolescence, most of the original assembly instructions and knowledge had been lost in the mists of time,” says Steve Cranstone, Link Microtek’s managing director. “So that did make it a challenging project, not least in recreating the exact same fully-custom end-plate castings, which form the precision interface with the avionics system.”

Unable to access the original mould for that crucial part, Link enlisted the help of a specialist casting company, who managed to reproduce it using the end plate from the original unit. “Once we had the new casting,” continued Cranstone, “it then had to undergo accurate machining in our in-house workshop to ensure that all the holes were exactly the right size and in exactly the right position.”

Functionally, the unit is a 4-channel, fan-cooled wideband test system for high-power microwave sources. It has two waveguide channels, implemented in WRD750 double-ridge waveguide, and two coaxial channels utilising 4-10GHz N-type connectors. All four channels have an input power rating of 200W CW.

During the process of recreating the test system, Link took the opportunity to make recommendations for improvements to the original design. Thermal performance was enhanced by incorporating additional fans and temperature-monitoring circuitry with LED warning indicators on all four channels.

An interlock connector was also designed-in to allow automatic shutdown of the transmitter if the input power to the test system exceeded a preset limit. Other minor improvements included a universal voltage input, a power-on indicator and additional lifting handles to facilitate transportation.

“Although some of the key microwave components for the unit were still readily available, others had originally been sourced from a now-defunct manufacturer and were therefore obsolete,” says Cranstone. “But as Link Microtek is the UK representative for leading RF and microwave component manufacturer L-3 Narda-MITEQ, we were able to quickly identify suitable alternatives from the company’s vast range and incorporate them into the design instead.”

However, the replacements were of a different shape to the original parts, so Link had to design and produce new brackets for them. In addition, the company fabricated the double-ridge waveguide components, carried out all the assembly work and undertook comprehensive testing of the finished unit. Cranstone again:

“As part of our obsolescence service, we produced a complete set of drawings, together with a parts list, a user manual and an acceptance-and-test procedure covering low-power and high-power testing at component and system level, electrical testing and EMF safety testing. So when the customer asked for a second unit several months later, we had all the necessary information to hand and could supply it without delay.”

With experienced microwave engineers and skilled craftsmen under one roof, Link Microtek was able not only to recreate the test system with the same form, fit and function as its original counterpart but also to update the design in line with modern standards.


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