What it takes to build an ELT tester

I love aviation. More specifically, I love the people who are passionate about aviation and the puzzle it can be. Neil Stone is a great example.

He’s 80 years old. He’s a pilot. He’s also an active airframe and powerplant (A&P) mechanic with inspection authorization (IA). He’s also taught himself electronics and industrial design.

In the last several years, he’s added computer programmer and manufacturer to his business card.

Those latter titles came as a result of his once attending an IA meeting where the topic of discussion turned to the then relatively new 406 MHz ELT.

“When it was mentioned that a suitable tester was a $4,000 investment, I started wondering if I could design a tester that would be more reasonably priced,” recalls Neil.

That’s despite the fact he “had no knowledge of the new beacons.”

Neil dove in.

“I started out by sending off for the literature on the $4,000 tester,” he says.

From that, he learned he’d have to back up a step or three and learn about COSPAS-SARSAT — an international “satellite-based search and rescue (SAR) distress alert detection and information distribution system” that is the backbone of all modern distress beacons — as well as their standards and measurement protocols.

User friendliness was added to affordability on the list of requirements for the tester. Neil settled on a simple lighting system.

“If the beacon complied with COSPAS-SARSAT specifications, the light would be green, if it did not the light would glow red,” he says.

A four-line, 80-character monochrome display to show the results of the measurements and message information would round out his tester.

From there Neil designed both 406 MHz and 121.5 MHz receivers. He then “examined and purchased several microprocessors to analyze the signals and decode the message that is part of the brief transmission made by the 406 MHz beacon.”

Microprocessor in hand, Neil set about learning how to program it. His long ago Radio Shack TRS80 programming experience was useful in learning the nuances of his selected microprocessor’s programming language.

Next up: Test the tester. For that, Neil designed a beacon signal source that not only complied with COSPAS-SARSAT specifications, but could also simulate various COSPAS-SARSAT specification failures.

“An ELT that produces a COSPAS-SARSAT failure doesn’t mean the unit is not working,” Neil notes. “However, it does mean the beacon transmission is not within the COSPAS-SARSAT specifications, which is one of the requirements for beacons using their system.”

Additional prototypes were built and sent to various maintenance shops for testing. As a result of the feedback Neil received, he added some memory so test results can be stored for later review and made some minor operational tweaks.

After weighing his options to outsource or manufacture the tester himself, Neil decided to tackle the last step himself as well.

“The end results so far have been very interesting,” he says.  “I did not anticipate international sales, which have included New Zealand, Italy, and Canada. Also, there have been several various government agencies and brisk interest from homebuilders groups.”

Neil’s original pricing goal was $500. He came close and priced his Creative Electronics’ ELT Test Model 1091 at $648.

Many complain about the “high cost” of aviation. Neil and his ELT Tester — and the journey to making it reality — is a great example of someone trying to do something about those high costs.