Broadband Antennas

Just what is a broadband system? The word "broadband" means different things in different applications. Federal Standard 1037C, Glossary of Telecommunication Terms, defines it in a vague way. Today, just about all communications systems fit our idea of "broadband," with the key concept being speed due to the number of bits that flow through the communication "pipe."

Before you select individual components for a broadband system, develop an understanding of what that system will be doing and what environment each component will operate in (outdoor, high heat, high noise, etc.). Create a block drawing of the major components, as a starting point.

Once you have a clear idea of which components are your core components, you can select the supporting components that match them. For example, select your routers, switches, antennas, and amplifiers before specifying your cabling.

This seems logical enough, but it's not always the way people proceed. One reason why they get hung up is they realize they'll be routing cabling through environmental air space, so they specify plenum cabling while this is on their mind. But that's out of sequence in the design process.

Obviously, you need broadband filters, couplers, and antennnas that meet your frequency requirements. But many other factors also apply. For example:

• Indoor or outdoor?
• In an enclosure, wall-mounted, or panel-mounted?
• Do you need a mast, tripod, or tower?
• Are connections coaxial or some other method?
• Is your broadband system providing stand-alone coverage, or is it part of an integrated wired/wireless system?

Careless installation of broadband components can severely limit performance. Some key issues to address:

• Follow the requirements of National Electrical Code, NFPA 70, Chapter 8.
• Do not "ground" the individual components. Bond them. The National Electrical Code, NFPA 70, provides the definitions of grounding (connect to the earth, or dirt) and bonding (create a metallic path to eliminate differences in potential). It also provides the bonding requirements in Article 250, Part V. Violating these results in undesired current flow and flashovers.
• Mechanical mounting. Is the mounting surface suitable to the anticipated mechanical stress? Is it secure, and does it provide the necessary protection?
• Location. Put as much distance as is practical away from power wiring. As with real estate, location is pretty critical.
• Access. You need to mount components such that they are reasonably well-protected from damage and, where possible, secure from unauthorized access. But you also need to make these accessible for maintenance, repair, and upgrades.
• Interference. Don't locate components close to utility lines or other sources of signal noise problems. Don't route cabling in runs parallel to power runs. Right angle is best, if practical.
• Aiming. In many applications, poor aiming of broadband antennas can degrade system performance below acceptable limits. Follow standard industry practices for the system you're installing.
• Obstructions. You're limited to how much power you can pump out, if broadcasting. If you're receiving, there's a limit to how strong that signal will be. In either case, you must consider instructions such as structural steel members of buildings. In many cases, such as when building out a wireless Internet system inside a commercial building, obstructions create gaps in coverage. Additional hardware (e.g., repeaters) is required to fill the gaps.