Site hardening is the process of enhancing a transmission site's ability to withstand damage from natural and manmade disasters. The payoff is the survival of two-way radio communications even in the harshest of conditions. But site hardening doesn't have to cost a fortune.

In Florida, the Polk County trunked radio system — which serves police, fire, EMS and other county agencies — survived Hurricane Charley's winds in 2004 because its eight transmission sites had been hardened prior to the storm's arrival — and because officials went the extra mile.

“The specs at the time called for towers to survive wind-loading of 85 mph, which was bogus,” said Ben Holycross, radio system manager for the Polk County Division of Emergency Management. “We built our towers to withstand 150 mph winds. That was a good thing — Hurricane Charley's winds were measured at 136 mph until the anemometer was blown away.”

Effective site hardening starts with an accurate threat assessment. The two aspects to be considered are natural threats and those caused by humans.

The kinds of natural threats that might be encountered depend on location. “Sites in the Northeast are vulnerable to snow, wind and flooding, while those in the Southeast have to survive hurricanes and tornadoes,” said Matt Foosaner, director of Sprint's emergency response team. “Meanwhile, transmission sites in California have to contend with wildfires, earthquakes and the chance of tsunamis.”

Manmade threats include industrial accidents, fire, vandalism and terrorist attacks. Carelessness also has to be considered. Sprint once lost a transmission shelter after a blizzard because a snowplow drove right through it.

“The key to assessing threats to your site is to take a step back and consider all reasonable possibilities,” said Art Vanags, director of North American systems integration project management for Motorola. “Do this right, and you will make accurate, meaningful conclusions about hardening your sites.”

After threats have been assessed, Holycross said that agencies should hire a qualified civil engineer to independently evaluate their sites. “A third-party engineer has the expertise to do the research accurately and to provide you with truthful answers unaffected by political or financial pressures,” he said.

Once the sites have been evaluated against the threat assessment, the next step is to decide what should be done and how to pay for it.

First things first: Do those upgrades that can be done for minimal money, and do them now. “All of the smaller LMR systems in this country could see a 50% improvement in performance by doing required maintenance on their antennas, tower-top preamps if they have them, and their hardline coax and grounding systems,” Holycross said. “This doesn't cost much money and only takes a few days to accomplish, but you'd be amazed just how many agencies throw up towers, then expect to use them without doing regular maintenance.”

Smart public safety agencies cut back grass and brush around their sites on an ongoing basis. This low-tech work doesn't cost much, but it makes a difference during wildfire season. “In California, I saw a few transmission sites in the midst of the burn area that survived thanks to preventive brush cutting,” Vanags said. “In cases where there was no fuel to feed the fire, it simply leaped over the buildings, leaving them safe and operational.”

With enough lobbying and public awareness, elected officials can be convinced to fund site-hardening projects. Once the money has been allocated, the following options are worth implementing.

Strengthen/raise the shelter

Polk County's transmission shelters have survived numerous hurricanes because “they are built of reinforced concrete and bolted to their foundations,” Holycross said. In those instances where shelters are framed, reinforce and secure them.

In areas where flooding is a problem, “it makes sense to physically raise the shelter 5 to 10 feet above ground level,” Foosaner said. “It sounds obvious to protect the electronics by getting them out of harm's way, but you would be amazed by how many agencies have not done this.”

Reinforce the tower

A transmission site is useless without its tower. The tower's structure should be reinforced to handle the load it has today with carrying capacity to spare. This will provide extra protection during high winds and ensure that future users won't compromise the tower's integrity when they add new antennas.

Add lightning protection

“We live in the lightning capital of the world,” Holycross said. “No other place gets as many lightning strikes as we do. This is why our sites have extensive grounding systems and lightning surge suppressors. The result is that we have never gone off-air due to a lightning strike. Yes, some of our surge suppressors have been melted, but the extra voltage has never made it inside the shelter to the electronics.”

Improve backup power

Without electricity, a transmission site is useless. This is why having properly serviced, adequately fueled electrical generators is a must. Holycross said to use propane as a fuel source, but not diesel. “Diesel fuel does literally go bad,” he said. “It doesn't take long for it to convert into something resembling a sponge. In contrast, you can leave propane stored in a tank for 50 years, and it will still be ready to burn when you need it.”

Hydrogen fuel cells are another option. “We are implementing these clean-burning cells as part of our green strategy,” Foosaner said. “Thanks to advances in fuel cell technology, this material is actually less volatile than natural gas or diesel, and it doesn't result in any hydrocarbon emissions.”

Because generators take time to kick in, transmission sites need to have an adequate supply of battery power from on-site uninterruptible power supplies (UPS). Although these battery banks often are configured as a stopgap to cover the few minutes that occur between the loss of main power and the generators' feed, smart agencies install enough capacity to provide a few hours' worth of power — at a minimum.

“You have to have enough battery power to keep the transmitter going until a tech can get there if the generator fails,” Vanags said. “Otherwise, you could lose the site after the UPS runs down.”

Ensure redundancy

It is imperative to have redundant signal paths between transmissions sites and the facilities that feed them. For example, those who rely on landlines to get signals to their sites should add a wireless backup path via microwave or WiMAX. “In hurricanes, I've noticed that the microwave system stays up when the telephone lines are lying on the ground,” Holycross said.

Equipment redundancy also is a must, as is a self-healing connection architecture. Equipment redundancy requires backup trunk controllers and other mission-critical components online and available at a separate location. A self-healing architecture means that if the line between a site and the origination point is broken, the signal can get there via another path. One proven way of doing this is to connect all the sites and the origination point together on a “ring-shaped” network. By being located as points on a continuous circle, signals can be sent to the sites in either direction. If a break occurs between headquarters and a site in one direction, the signal can be fed from the other.

Site hardening improves a radio system's resiliency and robustness, ensuring that it will survive when the going gets tough. The time to start the process is now.