Good Fences, Good Neighbors

Cell sites always have been lightning rods, but it wasn't until zoning boards and the public latched onto the idea that they're a health menace that they began taking their worst hits. Today, they're being accused of everything from causing cancer to interfering with motorized wheelchairs and cochlear implants.

Three trends in the industry are putting more people closer to more sites: aggressive build-outs, sites closer to street level for better coverage in urban areas, and the growing popularity of picocells to improve in-building coverage.

RF exposure usually is less of a concern at a tower site. For one, the RF that reaches the ground is minimal, and fencing around the site adds to that distance. For another, people climbing towers almost always are in the communications industry, where RF-safety training is mandatory. Not so with rooftops, where people can get as close as a few feet from an antenna. As a result, the FCC's maximum permissible exposure (MPE) guideline has two sets of exposure limits: uncontrolled exposure for the general public, and controlled exposure for those whose jobs involve working on or near sites.

One way to assess compliance is to measure RF levels at the site. That can take as much as a day at each site. The alternative is to collect information such as antenna model, frequency and power, and feed it into compliance software.

"For most cellular and PCS carriers, measurements (are) unnecessary," said Richard Biby, Sitesafe vice president of engineering. "The easiest and simplest way to do it that's 100% valid from an engineering standpoint is computations. If you can determine the closest distance that a human can come to your antenna, then you can do a worst-case analysis right there."

Two wild cards are foliage and reflections, variables that most software can't take into account. In those cases, field testing might be necessary.

"If they suspect reflection, then they go to the site and do a wideband test," said Reza Okravi, LCC senior manager of engineering. "That's a judgment call."

Some municipalities require measurements.

"When we have that requirement, we hire a third-party company," said Ben Andrzejewski, US West Wireless network director. "We have the equipment to do it ourselves, but generally we find it easier to hire a third party because it adds credibility."

Most carriers using software find that the vast majority of their sites are compliant. For sites that fail, field testing can identify any hot spots, but collecting and processing data can take a day or two per site. The least-intensive type is a narrowband study, which involves drawing gridlines around the site and using a wideband wattmeter to do hundreds of measurements. If that study confirms that the site isn't in compliance, the next step is a narrow-band study, where a spectrum analyzer measures the power-density level of a specific frequency.

One caveat: Field testing doesn't necessarily provide a complete picture. Any RF environment is dynamic, so it's helpful to know, for example, if a paging site is nearby.

"Paging sites aren't on all the time," Okravi said. "If the paging is off, you may think that you're in compliance. When it comes on, you may not be anymore."

WARNING: HIGH RF LEVELS If RF levels exceed MPE limits, common solutions include posting warning signs around the antenna or erecting a fence to restrict access to the non-compliant area. Less-desirable solutions are reducing power and re-orienting the antenna.

Compliance can get complicated on co-located sites. If the site creates an area where RF levels are too high, each carrier contributing 5% or more to that area shares the responsibility of bringing it back into compliance.

Regardless of whether the site is co-located, compliance is a work in progress. A significant change, such as a power increase or height decrease, can throw a site out of compliance.

"You really should re-run when you lower," said US West's Andrzejewski. "Nine-and-a-half times out of 10, it's not going to take you anyplace. But you're changing the configuration to some degree, and you should check that."

One possible exception is downtilting.

"A downtilt obviously provides a higher exposure level under the cell site," Okravi said. "But in most cases that I've seen, the downtilts generally are in the vicinity of 3 degrees to 10 degrees, (which) doesn't change the exposure level underneath the site that much."

Another concern is changes made by a fellow tenant. Both site-management companies and carriers that lease space to other carriers can require their tenants to alert them of any changes that might affect compliance. The rule of thumb is that the one making a change or moving onto the site is required to alert the other tenants. Even without a site-management company to act as an intermediary, the information usually flows freely.

"Generally, we see a 1-day turnaround for this information," said Bill Brickel, Cellular One - Kansas and Missouri director of technical services. "We have a process by which it is required via a co-location agreement to notify tenants any time site modifications are made."

A diligent site-management company can reduce the cost of compliance by maintaining an updated database of its tenants' equipment, power levels, frequencies and contact information. Site-acquisition companies also often collect information about the other tenants. Both can be tapped to streamline compliance computations.

"When we co-locate a carrier on our towers, we ask them for their antenna information and equipment types," said Robert Mawrey, Unisite vice president of systems and technology. "Over the past few years, we've built up a database that has a lot of detailed information on different manufacturers' equipment. So if they tell us what the model number is, we can often interpolate the characteristics we need to do both interference and, to some extent, health and safety."

If the company's portfolio includes rooftops, it's not uncommon to have it train the building's personnel about RF safety. Bottom line: a good management company can help reduce compliance costs.

"If a site is not well managed, meaning I don't know who the other carriers are and the management company isn't taking an active role, it becomes a financial factor that needs to be considered in the site-acquisition process," said Sitesafe's Biby. "In a purely legal way, the carrier is responsible. In a practical way, that carrier is going to need help."

Disclosing information about power and antennas doesn't faze most carriers. The biggest headache can be finding the right contact people at each carrier.

"The industry, in my opinion, works very well providing that information once a request is submitted," said US West's Andrzejewski. "It was a little rough going when we first started with this because you need to find all the contacts, and different companies have different people doing it. Once that got established, it runs like clockwork now."

That's not surprising, considering that the industry already has banded together to fund studies on RF's effect on health.

"We would definitely give up that information gladly," said Eric Hulander, U.S. Cellular manager of RF planning. "If it's something regarding safety, we're going to cooperate as best as we possibly can. It can be difficult to ferret out the information sometimes, but nobody ever says, 'Yes, I have that information, but I'm not going to let you have it.'"