GTRI Receives $4 Million to Redesign Air Traffic Control Radios

Tag : Intermediate Frequency Power Supply

Atlanta (June 16, 2008) —The Georgia Tech Research Institute (GTRI)has received a $4 million contract from the U.S. Air Force toredesign critical modules used in thousands of air traffic controlradios. First fielded in 1968, these ground-based units play avital role in keeping U.S. military aircraft safe, and the redesignshould help keep the radios on the job until newer designs canreplace them.
GTRI researchers Russell McCrory and Steve Thompson discussreplacement modules for air traffic control radios used by the U.S.Air Force. (Georgia Tech Photo: Gary Meek)
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The redesign task – which must be completed in a year –is both challenging and important, said Russell S. McCrory, a GTRIsenior research engineer. Some 7,500 of these ground communicationsradios – known as AN/GRT-21 and AN/GRT-22 transmitters andAN/GRR-23 and AN/GRR-24 receivers – are still in service.When they break down, they often require parts that are no longeravailable.

“This system has been in the field almost 40 yearsnow,” said McCrory, who is project director. “Manyparts now unavailable were originally manufactured by hand, andwould be very expensive to reproduce today just because of themanual labor involved.”

Among other things, GTRI engineers must find ways to replacenumerous semiconductor components, such as transistors and diodesthat are no longer manufactured. In some cases the original makersare no longer in business; in other cases the products are so oldthat no replacements are available.

Instead of trying to reproduce the original technology, GTRIengineers are designing replacement units that use only modernoff-the-shelf parts. The aim is to give the customer a replacementmodule that is plug-compatible with the original unit and does thesame job.

“We throw away the original design, and we make a unit withthe same size and the same function,” McCrory said. “Ifthe old unit had a certain meter reading to show a certaincondition, the new one should work identically.”

GTRI researchers Russell McCrory and Steve Thompson discussreplacement modules for air traffic control radios used by the U.S.Air Force. (Georgia Tech Photo: Gary Meek)
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The current $4.05 million contract covers redesign of five majorassemblies within the GRT/GRR, a complex system of receivers andtransmitters that operates in the VHF and UHF radio-frequencybands. The five assemblies include a dual-band power amplifierunit, an intermediate-frequency (IF) amplifier, a mixer-multiplier,a power supply unit and a synthesizer.

“This work provides both a technical challenge and ademonstration of GTRI’s commitment to deliver onfast-reaction contracts,” McCrory said. “Within 12months, GTRI will produce five complete new designs including alldata necessary for the government to obtain competitive bids frommanufacturers, engineer prototypes, obtain the initial devices froman outside vendor and update user and operator manuals.”

He said that GTRI’s changes to the dual-band power amplifierwill retain that assembly’s unusual capacity to broadcast a10-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 thatcan be processed by the receiver – and also modify the IF(intermediate frequency) amplifier in the receiver, which amplifiesthe received radio signals. And a new power supply will increasereliability.

In replacing the current radio’s original analog components,GTRI engineers are crafting a system that is still all-analog butuses new off-the-shelf technology that is widely available. Thisapproach allows the Air Force to ask for competitive bids fromnumerous manufacturers rather than relying on a sole source.


Christian Michelson (left), a GTRI student assistant, and GTRIresearchers Steve Thompson and Russell McCrory, examine modules forair traffic control radios used by the U.S. Air Force. (GeorgiaTech Photo: Gary Meek)
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The savings can be substantial, McCrory said. He cites a competingapproach that would have cost the government about $500,000 fordrawings of one obsolete transistor in the GRT system, and thenanother $500,000 for the first transistor reproduced from thosedrawings.

“Our approach will result in major savings for the militaryversus trying to remanufacture the original components,” hesaid.

GTRI’s role in maintaining the GRT/GRR radios has evolvedover several years. In 1999 the Warner Robins Air Logistics Centerat Georgia’s Robins Air Force Base took over engineeringresponsibility for the radios, and in 2005 GTRI engineers wereasked to produce GRT/GRR technical documentation.

Subsequently, GTRI created a support roadmap for sustaining theunits until they are retired, and the analysis showed that majorradio components needed to be replaced to meet this goal.

McCrory adds that his team has made extensive use of GTRI’sSUSTAIN software in helping to identify modules requiring redesignand to justify funding requests. SUSTAIN is a multi-part managementtool that helps guide maintenance/sustainment decisions on oldermilitary systems.

Eventually, McCrory explains, all Department of Defense radios aredue to be replaced by a reprogrammable, software-based technologyknown as the Joint Tactical Radio System (JTRS). Though the firstJTRS systems could begin replacing high-priority radios as early as2011, ground radios like the GRT/GRR systems are scheduled forreplacement much later – probably not until 2020 to 2025.That means GRT/GRR radios could require maintenance for another 18years.

GTRI expects its redesign to help ease the Air Force’s partsinventory and logistics tasks for these radios. The newdual-band-power amplifier is expected to replace three oldermodels, and the new mixer multiplier will replace two older models.

One of GTRI’s top goals, McCrory said, is to make it cheaperfor the Air Force to simply plug in a new module than to repair anold one. That would not only save money and time, but also bringbroken units back online faster.

“The Air Force, in conjunction with Tobyhanna Army Depotwhich does the maintenance, has done just a wonderful job keepingthis system in the field,” McCrory said. “We’retrying to help them continue to do that, while keeping costs undercontrol.”

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Writer : Rick Robinson
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