Whether you are purchasing a cellular tower for the first or 50th time, there are many decisions to make about the structure supporting the antennas that provide your cellular service. Because constant, consistent coverage is imperative in today's cellular environment, assuring customers continued service is a priority for cellular operators.

Choosing the right tower for the cell site's outside plant can help meet that service priority. A tower is the backbone of the outside plant, and cellular towers in particular are unique to the tower industry. When purchasing a tower, find a manufacturer that has specific experience in building and erecting cellular towers.

Several areas of tower manufacturing should be examined when purchasing a tower as part of the outside plant. The possibility of additional future antenna loads, safety considerations, general specifications, tower construction, warranties and a fair comparison of vendors' bids are all essential factors in choosing the right cellular tower.

Getting to the basics
In the initial stages of setting specifications and choosing a tower vendor, you should determine basic requirements by evaluating the site and establishing the size of the tower you will need.

Initial evaluation involves choosing the tower site relative to the targeted area and determining how much land will be needed for the tower. The tower's height must meet Federal Aviation Administration navigational restrictions, and the frequencies needed should be approved by the Federal Communications Commission for the cell-site area. The overall soil condition in the area should be gauged initially, attempting to avoid sites that are all rock, swamp or sand. A detailed soil evaluation should be conducted before the tower is erected.

Once the site has been selected, you should develop tower specifications with the tower manufacturer as guided by federal and local ordinances. The Electronic Industries Association (EIA) sets specific standards intended to dictate minimum criteria for the design, fabrication and construction of antenna-supporting structures. Specifically, a cellular tower should meet the latest version of the EIA/TIA-222-E standard, which addresses towers. Copies of the EIA/TIA-222-E "structural standard for steel antenna towers and antenna supporting structures" may be obtained from the EIA Standards Sales Department by calling 202-457-4966.

Local standards are sometimes more stringent than federal standards and the tower must conform to local ordinances. Many cities require a state-certified engineer to seal the tower design as meeting EIA standards and local codes before a permit is issued to erect a tower. If a tower should fail for any reason, the cellular operator will be charged with proving the tower met all required standards from the outset. Sealed designs provide that proof. However, when comparing bids for a tower, be sure the sealed designs are included in the total price. Some vendors charge extra for sealed drawings.

Choice and flexibility
Flexibility in design is the key to expansion. Design ahead for the maximum antenna and dish loads. If a tower is not designed for growth when it is constructed, it frequently cannot be upgraded without significant additional cost. It is not a good idea to merely increase future antenna and dish loads. Estimating the future antenna and dish load is much more accurate for ensuring that the tower has capacity for growth.

Lloyd Swetnam, supervisor of construction for GTE MobilNet, Houston, said that he wants a tower designed with the capacity to meet microwave or cellular capacity. "You can't predict the industry" he said. "In some cases, more dishes may need to be added, which consequently increases the wind load. This all enters into a custom design request."

Design flexibility also means providing a customized tower to meet the cellular operator's needs. Cellular towers generally have platforms and special mounts for antennas. Because cellular tower design is complex, manufacturer flexibility is important.

Be sure that custom design doesn't mean custom time. The manufacturer should have the ability to provide a custom-designed tower that meets the cellular operator's deadline and budget. Air-time means money to the cellular operator, and he or she should expect timely delivery.

A cellular tower can be self-supporting or guyed. Guyed towers have guy wires extending from the tower to the ground for stability. Most rural service areas (RSAs) use guyed towers while metropolitan statistical areas (MSAs) mostly use self-supporting towers. Guyed towers require more land surrounding the tower because the wires extend in a radius equaling 80% of the tower height as measured from the base of the tower. The tower will be more expensive with a smaller guy radius because the guy cables resist the horizontal wind load, and the more vertical they become, the less effective they are. Larger steel members and additional bracing are required to bear the increased torque and horizontal load.

There are three choices in the structure of the tower's legs: solid, tubular or angular. Solid and tubular legs offer benefits over the angular leg for cellular tower construction. When compared to angle legs, solid and tubular legs carry a lower wind load, have more efficient cross-sections and are manufactured in many sizes.

Solid legs are advantageous because corrosion is limited to the outside of the leg where it can be observed. A tubular leg may corrode from the inside, and the corrosion will not be found until it has eroded through to the outside of the leg. This could occur from condensation or if a weep hole or drainage hole in a tubular-leg tower becomes blocked with debris, allowing water to accumulate. The result is that in cold climates, water turns to ice and can crack or split the leg.

Splitting is rare, and corrosion is not likely to occur for many years after installation. But when you consider the similar cost of a solid leg at the time of purchase vs. the repair cost of a split or corroded leg, a solid-leg tower often is the design choice in the cellular industry.

Donald Kantner, a purchasing engineer with Ameritech Mobile Communications, said his priority in purchasing a tower is quality. "Solid leg construction makes regular maintenance much simpler and eliminates the worry of corrosion or splitting as with a hollow leg."

Other tower construction options include bolt-up or all-welded construction. Most self-supporting towers are bolt-up construction, and most guyed towers are all-welded construction. Bolt-up construction means the tower is bolted together in sections during erection. All-welded construction has the bracing welded together in sections before erection.

All-welded sections can be more expensive than bolt-up sections, but the savings in erection costs, time and maintenance costs can offset the more expensive materials.

If it is important to the cellular operator to get a cell site on the air quickly, especially when dealing with a 500-foot RSA tower, an all-welded section can be installed in about half the time of a bolt-up tower. When comparing bids involving all-welded and bolt-up towers, be sure to compare the sum of the tower material cost and erection cost.

Evaluating the site
Ideally, the site must be level and accessible by a semi-truck and installation equipment, such as a crane. The route to the site should be clear of overhead obstructions, such as power lines or trees. The underground, where the foundation will he poured should he checked for utility lines

The ground should also be evaluated for soil condition. The EIA has created standard soil design parameters for what it calls normal soil. This creates uniform foundation design criteria to compare competitive bids. Determining the actual site soil condition should be delegated to a geotechnical engineer familiar with tower and foundation construction requirements. Soil testing provides information on seismic considerations and frost susceptibility. It also provides insights as to which type of excavation is appropriate.

The soil condition may turn out to be a costly surprise if a tower manufacturer assumes the soil condition at the site is normal. According to EIA/TIA-222-E, normal soil is defined as a cohesive soil with an allowable net vertical bearing capacity of 4,000 pounds per square foot and an allowable net horizontal pressure of 400 pounds per square foot per lineal foot of depth. Rock, non-cohesive solids or saturated or submerged solids are not to be considered normal soil.

From the cellular operator's point of view, this definition is significant when comparing bids. Few places in the country have normal soil conditions as defined by the EIA. Unfortunately, a vendor may submit an unrealistically low bid on the foundation, citing normal soil, then later increase the foundation's price significantly. Unless a detailed soil analysis has been conducted and made available to vendors ignore the foundation cost when you compare various bids.

When you are responsible for the operation of the cell site's outside plant, safety is a prime consideration - as it relates to the technicians working around the outside plant and to antennas and equipment.

Determining the wind and ice load to use in the tower design is critical to its stability. Be sure all vendors are using the same wind and ice load in their calculations. The EIA wrote guidelines to set a uniform design standard for communications towers throughout the country. These standards are based on the ANSI A58.1 publication, which serves as a guide for most building codes in the country with the exception of the Uniform Building Code (UBC). Generally, if your tower is located in the western United States, the tower will be designed according to the UBC.

The EIA standard specifies a minimum design wind velocity on a county-by-county basis, but it does not make any recommendations regarding radial ice accumulation. Specific areas of the country, such as the Great Lakes coastlines and the top of the Rocky Mountains, are considered special wind regions in which the EIA makes no wind velocity recommendations. The burden of selecting the correct design wind velocity and ice accumulation lies with the tower purchaser. If you do not specify wind accumulation, this critical design consideration may be ignored by some tower manufacturers in this highly competitive market, according to Kevin Bauman, an engineer with Paul J. Ford and Company, Columbus, OH, an engineering firm.

In most locations, the maximum design wind velocity and ice accumulation does not occur simultaneously. For this reason, the EIA standard allows a 25% reduction in wind load when ice is considered. This wind load reduction will often be automatically considered by the tower manufacturers unless the tower purchaser specifically states that the maximum wind and ice should be considered to occur simultaneously.

Lighting will be dictated by the FAA and the FCC. As a general rule, towers more than 200 feet are required to have lighting. However, if the tower is within five miles of a heliport or airport, it may be require lighting even if it is less than 200 feet tall For more information on lighting specifications, see "Tower Safety" on page 28.

Be sure to find out if the tower requires painting. Paint must meet the FAA standard of international airways alternating bands of orange and white. If painting is required, consider having the factory paint the steel during manufacturing. Factory-painted towers have a better seal and a more even coating because they are painted in a controlled environment. A factory-painted tower also can be less expensive in the long run than a field-painted tower that may have uneven applications, requiring more frequent repainting.

Wilson said he always has the manufacturer paint the tower in the factory. "It is much more cost-effective to have a tower factory-painted when you consider the time it would take to paint it in the field," he said. "And while you can erect a tower year round, you cannot paint it in the field year round."

Another safety precaution is installing a ladder vs. step bolts. If a tower has at least a 4-foot face, a ladder can be attached to the inside of the face. A safety climb device such as a bar or cable that runs vertically with the ladder, also should be available for a climber to attach a safety belt.

Step bolts cause injury and can be hazardous to the climber. Step bolts extend from a member of the tower perpendicularly. Climbers have caught clothing on the bolts or bumped their heads on the extensions while climbing. A ladder is safer and more maneuverable.

Anti-climb devices can be installed to prevent unauthorized personnel from climbing the tower, and often a barrier or fence is put up around the base of the tower.

By now, it is evident that numerous options exist when purchasing a tower When evaluating bids, be sure the specifications are equivalent. Ensure that all bids are equivalent as they relate to:

wind and ice load.
antennas, dishes and line loadings (including azimuths).
consistency in tower leg construction (solid, tubular or angular).
all-welded vs bolt-up.
inclusion of sealed drawings.
EIA-applied standards
painting.
lighting.
the foundation price based on a detailed soil report.
freight charges (including off-loading).
FOB location.
delivery times.

It is important that all options are broken out into line items on the bid specifications. This allows you to add and subtract options without greatly affecting the calculations of the total cost.

Also thoroughly examine a tower manufacturer's warranty. Often, it is little more than a long-term employment contract for parts, material and labor. The fine print in a 5-, 10- or 20-year warranty may require that the cellular operator have the manufacturer's personnel perform periodic inspections at a cost of $750-$1,000 each.

Cellular options
Many decisions must be made in addition to tower design and construction when erecting a cellular tower. Such options as waveguide bridges, antenna mounts, platforms and grounding should all be considered when purchasing a tower.

A waveguide bridge is a support structure that holds cable in place between the tower and the building or a ground post. Be sure to specify the height, length and width of the waveguide bridge.

Identify the specific antennas and dishes and respective azimuths so a proper mount can be sized and built. Antennas mounted at the same level require a certain amount of separation. Armed with correct information, the manufacturer will build the mounts that project the antenna the required number of feet out from the tower to maintain a minimum separation.

When requesting a quote, ask that the antenna and line installation cost be broken out as separate line items. Line installations should be charged on a per-foot basis and antennas on a per-unit basis. This is beneficial if the number of antennas or lines changes - the cost difference is clearly shown.

Specify whether your tower will require a platform and the height at which it is to be installed. Also indicate whether standard EIA grounding or special ring grounding will be required.

Checking a manufacturer's insurance coverage is a good gauge of standing. Tower manufacturers should have at least $500,000 basic general liability, plus $1 million minimum umbrella coverage. The manufacturer's subcontractors should also carry as much coverage and an all-states-endorsement workmen's compensation. An installation floater policy, which covers care custody and control, is another form of insurance that tower manufacturers and subcontractors should carry. This means that all materials in the care, custody and control of the manufacturer are covered. Be sure a manufacturer's bid has a waiver of subrogation and lists the purchaser as additionally insured. Many manufacturers fail to meet these requirements, so to ensure the highest standards are met, include those requirements in a request for bid.

A manufacturer's independent subcontractors should also have at least 10 years of experience in the industry. Check references. For a more objective set of references, ask for work done in the past month or two. Watch the work as it is being done in the factory. A reputable vendor should be more than willing to offer a facility tour.

Because a product that has a 30-year plus lifespan needs long-term support, be sure the manufacturer is financially stable. Examine the Dun & Bradstreet reports that apply to the company.

It is also wise to request a lien waiver from the manufacturer that ensures that it has paid all of its subcontractors. This assures you that no liens exist and that a subcontractor will not approach you for payment.

Assessing your choices
Foremost, you should seek a vendor that has experience with manufacturing cellular towers because these towers have unique requirements. That experience should extend into all areas of tower construction. Seek out vendors that have been in the business at least 20 years and find out how much of that experience is with tower construction specifically.

Kautner said flexibility on the part of the tower manufacturer is extremely important in meeting a cellular carrier's varying demands. "If I say I need a tower by the end of November, and the schedule changes such that I will need it in half that time, I will need a vendor not only with flexibility but an understanding that things change."

A manufacturer should understand that last-minute changes are part of the industry course and don't necessarily have to mean an increased cost.

When service and coverage are your priorities, purchasing the right tower is a significant decision in providing the most effective cell site. Planning for future antenna load, safety considerations, general specifications, tower construction, warranties and a fair comparison of vendors and vendors' bids are all essential factors in choosing a cellular tower that will most effectively meet the needs of your service area.