LAS VEGAS — In 1999, the city of Phoenix decided that it needed to replace its legacy radio system, which was using four-decades-old technology and was fraught with overloaded frequencies. The city also wanted a state-of-the-art system robust enough to accommodate police, fire, public works and other agencies, all of which were operating their own systems.

The city eventually purchased a 700/800 MHz trunked, simulcast system from Motorola that offers 117 frequencies and covers 2,000 square miles. Leif Anderson, deputy chief of the Phoenix Fire Department, speaking yesterday at the Association of Public-Safety Communications Officials annual conference, described it as a “system on steroids.”

“We got a bad-ass radio system,” he said.

Nevertheless, the law of unintended consequences soon kicked in, as the fire department discovered that the trunked system wasn’t well suited for communications in the “hazard zone,” Anderson said.

“Trunked radio systems are complex systems specifically set up and designed to maximize capacity, and to let a [large number of] users to talk over a very big area” he said. “The mismatch here is that those aren’t the requirements of the hazard zone.”

The great fear was that a trunked system would be unreliable on the fireground, i.e., hazard zone, in certain situations, which is a big problem because firefighters need communications that are simple, reliable and predictable, according to Anderson.

“If you can’t talk to the tower, or the tower can’t talk to you, you can’t talk to anybody,” he said. “We established a long time ago that that is an unacceptable situation. That’s a mayday situation. … It’s bred into us — if you lose the ability to communicate, you have to grab your partner and get out.”

So, the fire department went back to its VHF analog simplex system for fireground communications. Each firefighter is equipped with an analog radio, while officers carry both an analog radio, which they use to communicate with firefighters in the hazard zone, and a digital trunked radio that they use to communicate outside the hazard zone.

Of course, that is hardly an ideal situation, so the department, working with the Phoenix Information Services Department, has been experimenting with ways for the analog and digital systems to communicate with each other. The most promising to date involves the use of digital vehicle repeaters that would convert analog transmissions to digital, and vice versa. “We looked at this first because we thought it would be the most cost-effective and viable approach,” Anderson said.

It also turned out to be the most effective. Tests were conducted that involved 11 buildings — including high-rises, big box structures and small box structures, all of which typically present a challenging communications environment — and firefighters who were put into scenarios they would face during an actual incident. The results were impressive: 1,350 successful transmissions were executed, with just 32 failures. Of those failures, 24 involved firefighters who were in an elevator.

“When you compare [all of the approaches], this was the most successful,” Anderson said, adding that the fire department is now considering the placement of DVRs in every fire and EMS vehicle.

Even if that happens, more challenges are sure to pop up, Anderson said.

“This is a moving target,” he said. “As we’re sitting here talking, things are changing — trees are growing, buildings are being built and [the population is growing]. The amount of land that has been annexed in the area we serve over the last seven years is incredible. So we have to continuously reassess what our requirements are and what our options are.”

But the department also has to guard against paralysis by analysis, Anderson said.

“It’s like when you’re shopping for a car. When you need a car you have to buy one — you can’t keep shopping forever.”