The Maple Bluff (Wis.) Fire Department recently tested different manufactures’ analog and digital radios systems. The combination department found that next-generation digital vocoders filtered out interfering noise that affects voice clarity and volume on the fireground, Chief Joshua Ripp said.

Ripp and his team of firefighters put radios through a battery of voice tests to determine which was most intelligible on the fireground (see below for list of radios). They were running tests to determine which brand and version to buy, because their county soon will replace its current VHF conventional, countywide system to a 12- to 13-channel, VHF P25 trunk system.

“Narrowbanding goes into effect in 2013,” Ripp said. “So we are looking at different radios and technologies out there and trying to figure out what a good radio for us would be.”

Ripp said a new radio system also was needed under narrowbanding mandates that will force them to move to a digital system by 2013.

“It is one of those issues that I think we need to work on it because the next narrow-banding is going to go to 6 ¼ MHz voice transmission and there’s no way you can do it with analog,” he said. “If we get forced down that road it has to be digital.”

Four full-time staffers, eight interns and 12 volunteers tested analog and digital radios — ones without speaker microphones — with a specific focus on audio quality. They first recorded an emergency message and used it in the field instead of using live voices, “just to make sure it was consistent,” Ripp said. Then, the assistant chief stood by a fire truck’s hydraulic pump panel with a radio and transmitted the pre-recorded message. They continued the process with each manufacturer’s radio, transmissions were received by a scanner and then dumped into video-recording equipment, he said.

Ripp emphasized that although the tests have been completed, the department has not yet purchased radios nor endorsed any products. However, he said they found that the key improvement to digital voice was the use of next-generation vocoders, as compared on two different models of EF Johnson Technologies’ radios.

“When you compare the older vocoder to the newer on the two EFJ radios — v1.4 and v1.6 software of the AMBE +2 vocoder — there is a marked improvement between them and how they handle the high-noise environment,” he said. “We found out is that there are definite improvements in the different versions of that vocoder.”

There was still an issue with loud noises being heard over the radio, Ripp said. However, the vocoder-enabled radios were able to process out the noise and send more intelligible voice. Yet PASS alarms’ frequency and decibels still cause an issue, regardless of analog or digital radios are being used. As a result, he doesn’t believe the technology is ready for hazard-zone communications, and manufacturers need to improve noise cancellation software before firefighters with SCBA can count on digital signals. Indeed, they should work with NIST's current tests on digital radios and how they will help manufacturers meet firefighters’ communications needs.

“I think we are at a point now where the manufacturers are getting up to the plate and doing what needs to be done versus telling everyone they are using the radios wrong,” Ripp said. “That’s kind of my impression of what’s happened to this point is that radios didn’t perform as expected, and it was always blamed on the people using them. The radios now are getting designed to handle the specific voice issues popping up.”

Visit the Web site to view a video of the tests.

Models Tested:

  • Kenwood TK-5210
  • Motorola XTS-2500
  • Motorola XTS-5000
  • Motorola APX-7000
  • EF Johnson SL 5100
  • Tait 9135
  • ICOM 9011