Maintaining Air-Traffic Radio with Redesigned Modules

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GTRI engineers are helping keep air traffic control radios on the job until newer designs can replace them. The radios—known as An/GRT-21 and An/GRT-22 transmitters and An/GRR-23 and An/GRR-24 receivers—first went into service in 1968, and about 7,500 are still on the job.

“Many parts now unavailable were originally manufactured by hand, and would be very expensive to reproduce today because of the manual labor involved,” said Russell S. McCrory, a GTRI senior research engineer. “Even more challenging are semiconductor components, such as transistors and diodes, that are no longer manufactured.”

Eventually, all Department of Defense radios are due to be replaced by a reprogrammable software-based technology known as the Joint Tactical Radio System (JTRS). Under current timetables, however, the GRT/GRR ground radios will wait for replacement until 2020-2025.

In 1999, engineering responsibility for the radios was moved to the Warner Robins Air Logistics Center in Georgia. Currently, GTRI has a contract to redesign five major assemblies within the GRT/GRR. A$750,000 award is funding the first redesign—the system’s 10-watt dual-band power amplifier unit.

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 provide a readily available replacement module that is plug-compatible with the original unit and does exactly the same job.

GTRI’s approach enables the military to ask for competitive bids from numerous manufacturers rather than relying on a sole source. “This should result in major savings for the Air Force, versus trying to remanufacture the original components,” McCrory said.

If GTRI redesigns all five GRT/GRR units listed in the current contract, overall funding is expected to total $5.4 million. In addition to the dual-band power amplifier, the contract covers redesign of an IF amplifier, a mixer-multiplier, a power supply unitand a synthesizer.

In many cases, McCrory said, his team’s redesigns may allow radios to not only keep working but also to operate more effectively. For example, a redesigned synthesizer unit could dramatically reduce the complexity of tuning GRT/GRR radios, which currently are retuned through laborious settings changes. In addition, the new dual-band power amplifier is expected to replace three older models, easing parts inventory tasks.

One of GTRI’s top goals is to make it cheaper for the Air Force to simply plug in a new module than to repair an old one. The difference could save not only money and man hours, but also bring broken units back online faster.