Posted June 16, 2008 Atlanta
Research News & Publications Office
Contact John Toon
Work will allow vintage devices for continue operating
The Georgia Tech Research Institute (GTRI) has received a $4 million contract from the U.S. Air Force to redesign critical modules used in thousands of air traffic control radios. First fielded in 1968, these ground-based units play a vital role in keeping U.S. military aircraft safe, and the redesign should help keep the radios on the job until newer designs can replace them.
The redesign task - which must be completed in a year - is both challenging and important, said Russell S. McCrory, a GTRI senior research engineer. Some 7,500 of these ground communications radios - known as AN/GRT-21 and AN/GRT-22 transmitters and AN/GRR-23 and AN/GRR-24 receivers - are still in service. When they break down, they often require parts that are no longer available.
"This system has been in the field almost 40 years now," said McCrory, who is project director. "Many parts now unavailable were originally manufactured by hand, and would be very expensive to reproduce today just because of the manual labor involved."
Among other things, GTRI engineers must find ways to replace numerous semiconductor components, such as transistors and diodes that are no longer manufactured. In some cases the original makers are no longer in business; in other cases the products are so old that no replacements are available.
Instead of trying to reproduce the original technology, GTRI engineers are designing replacement units that use only modern off-the-shelf parts. The aim is to give the customer a replacement module that is plug-compatible with the original unit and does the same job.
"We throw away the original design, and we make a unit with the same size and the same function," McCrory said. "If the old unit had a certain meter reading to show a certain condition, the new one should work identically."
The current $4.05 million contract covers redesign of five major assemblies within the GRT/GRR, a complex system of receivers and transmitters that operates in the VHF and UHF radio-frequency bands. The five assemblies include a dual-band power amplifier unit, an intermediate-frequency (IF) amplifier, a mixer-multiplier, a power supply unit and a synthesizer.
"This work provides both a technical challenge and a demonstration of GTRI's commitment to deliver on fast-reaction contracts," McCrory said. "Within 12 months, GTRI will produce five complete new designs including all data necessary for the government to obtain competitive bids from manufacturers, engineer prototypes, obtain the initial devices from an outside vendor and update user and operator manuals."
He said that GTRI's changes to the dual-band power amplifier will retain that assembly's unusual capacity to broadcast a 10-watt radio signal in either the VHF or UHF bands.
In addition, the new design will re-engineer the mixer multiplier - a unit that converts received frequencies to a range that can be processed by the receiver - and also modify the IF (intermediate frequency) amplifier in the receiver, which amplifies the received radio signals. And a new power supply will increase reliability.
In replacing the current radio's original analog components, GTRI engineers are crafting a system that is still all-analog but uses new off-the-shelf technology that is widely available. This approach allows the Air Force to ask for competitive bids from numerous manufacturers rather than relying on a sole source.
The savings can be substantial, McCrory said. He cites a competing approach that would have cost the government about $500,000 for drawings of one obsolete transistor in the GRT system, and then another $500,000 for the first transistor reproduced from those drawings.
"Our approach will result in major savings for the military versus trying to remanufacture the original components," he said.
GTRI's role in maintaining the GRT/GRR radios has evolved over several years. In 1999 the Warner Robins Air Logistics Center at Georgia's Robins Air Force Base took over engineering responsibility for the radios, and in 2005 GTRI engineers were asked to produce GRT/GRR technical documentation.
Subsequently, GTRI created a support roadmap for sustaining the units until they are retired, and the analysis showed that major radio components needed to be replaced to meet this goal.
McCrory adds that his team has made extensive use of GTRI's SUSTAIN software in helping to identify modules requiring redesign and to justify funding requests. SUSTAIN is a multi-part management tool that helps guide maintenance/sustainment decisions on older military systems.
Eventually, McCrory explains, all Department of Defense radios are due to be replaced by a reprogrammable, software-based technology known as the Joint Tactical Radio System (JTRS). Though the first JTRS systems could begin replacing high-priority radios as early as 2011, ground radios like the GRT/GRR systems are scheduled for replacement much later - probably not until 2020 to 2025. That means GRT/GRR radios could require maintenance for another 18 years.
GTRI expects its redesign to help ease the Air Force's parts inventory and logistics tasks for these radios. The new dual-band-power amplifier is expected to replace three older models, and the new mixer multiplier will replace two older models.
One of GTRI's top goals, McCrory said, is to make it cheaper for the Air Force to simply plug in a new module than to repair an old one. That would not only save money and time, but also bring broken units back online faster.
'The Air Force, in conjunction with Tobyhanna Army Depot which does the maintenance, has done just a wonderful job keeping this system in the field," McCrory said. "We're trying to help them continue to do that, while keeping costs under control."
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