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RF is commonly used in the wireless communications industry to describe equipment using radio frequency waves to transmit sounds and data from one point to another. In computer networking, RF is used to describe network devices(hubs, bridges, etc.) that transmit data signals using radio waves instead of datacables or telephone lines. |
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Even though the phrase "RF wireless networking" might seem mysterious, the underlying technology is very common. It uses radio waves, the same type of energy used to transmit radio and television broadcasts. Two-way radios and walkie-talkies also use this technology.
The space program utilizes radio waves to control computers onboard space capsules and probes, and receive signals from other devices. Remember the video broadcasts from the surface of the moon? The color photographs of the surface of Mars? All of these were translated into radio waves and transmitted to Earth using radio technology.
Thinking about radio and TV, you can probably already identify some of the components needed to make RF wireless networking work: a radio transmitter, a radio receiver, an antenna, and a cable from the antenna to the receiver or transmitter. Add a couple of other components to protect the equipment—such as lightning arrestors and noise filters—and you've pretty much listed what you need.
You thought this was going to be complicated, didn't you? In the next few sections we'll describe what is involved in transmitting data over a radio frequency and how a wireless network connection can reliably be established. |
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| There are several components required to implement an RF wireless network link : |
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Some manufacturers sell their wireless bridges in separate units. In such instances, the physical radio/bridge unit has a base cost. Software features, such as individual protocol routing and encryption, are sold as a separate unit. However, these may be required in your implementation. Be sure to define your needs completely to the reseller/integrator/installer who installs your wireless connection. |
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For all wireless installations there must be a cable which connects the antenna to the radio in the wireless bridge. Because it runs to the outside of the building, this is called an external cable. When purchasing all the components as part of a kit, an external cable is included. Depending on where the wireless bridge is located inside your building, and where the antenna is mounted, an additional length of cable may be required.
In order to keep the wireless system within specifications, it is important to minimize the length of the cable. If necessary, it is possible to locate the wireless bridge at one location in your building and run a network cable from it to your network connection at an alternate location in the building. Be sure to physically secure the bridge if it is located in a public area. |
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Since external antennas are involved, the threat of a lightning strike can be very real. Make sure that proper measures are implemented to minimize the risk of lightning strikes. Most manufacturers of wireless bridges sell an optional device called a lightning arrestor. It is normally installed between the antenna and the bridge. Also make sure the antenna is properly grounded. |
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Some manufacturers provide another optional component known generally as an emissions filter. It reduces the level of extraneous noise that might interfere with the electrical signal on its way from the antenna to the wireless bridge. It also is installed inline between the antenna and bridge. |
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When it is not possible to obtain a clear line-of-sight between the two antennas involved in a wireless connection, a mast or radio tower may provide additional height for the antenna, clearing obstacles such as trees or buildings which lie in the path of the radio signal.Masts are generally mounted on the roof and may be 10-50 feet in height. If a mast is used in your implementation, be sure it is tied down properly to minimize the risk of wind damage.
Radio towers are generally independent structures erected to raise antennas when extended distances are desired. They may also be required when tall buildings (larger than three stories) or topographical features lie directly in the path of the radio signal between two antennas. Towers can be erected at heights of 50 feet and higher. Obviously, depending on the application, the cost of erecting tall towers can be prohibitive. |
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A network data cable is required to connect the wireless bridge to your internal network (to a hub, switch, or repeater). This cable is generally the responsibility of the individual entity. If the wireless bridge is a significant distance from the network equipment, installation of this cable may require a cable installer. In this case, be sure to discuss the cable run with your wireless installer when the system is being specified. |
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