Cisco AIR-ANT2420V-N= Datasheet download pdf (Page 6)

The Physical Environment

After mobility issues are resolved, the physical environment must be examined. While the area of coverage is the

most important factor for antenna selection, it is not the sole decision criterion. Building construction, ceiling height,

internal obstructions, available mounting locations, and the customer’s aesthetic desires also must be considered.

Cement and steel construction have different radio propagation characteristics. Internal obstructions such as

product inventory and racking in warehousing environments are factors. In outdoor environments, many objects

can affect antenna patterns, including trees, vehicles, and buildings, to name a few.

The Network Connections

Cisco Aironet access points use a 10/100/1000-Mb Ethernet connection. Typically the access point is in the same

location as the antenna. While it may seem that the best place to put the access point is in a wiring closet with the

other network components, such as switches, hubs, and routers, this is not the case. The antenna must be placed

in an area that provides the best coverage (determined by a site survey).

Many people new to wireless LANs want to locate the access points in the wiring closet and connect the antenna

using RF coax. Antenna cable introduces losses in the antenna system on both the transmitter and the receiver. As

the length of cable increases, so does the amount of loss introduced. To operate at optimum efficiency, cable runs

should be kept as short as possible. (See the Cabling section in this document for more information.)

Building Construction

The density of the materials used in a building's construction determines the number of walls the RF signal can

pass through and still maintain adequate coverage. Following are a few examples. The actual effect on the RF

must be tested at the site, and therefore a site survey is recommended.

Paper and vinyl walls have very little effect on signal penetration. Solid walls and floors and precast concrete walls

can limit signal penetration to one or two walls without degrading coverage. This may vary widely based on any

steel reinforcing within the concrete. Concrete and concrete block walls may limit signal penetration to three or four

walls. Wood or drywall typically allow for adequate penetration through five or six walls. A thick metal wall reflects

signals, resulting in poor penetration. Steel-reinforced concrete flooring will restrict coverage between floors to

perhaps one or two floors.

Recommendations for some common installation environments are outlined below:

●

Warehousing/manufacturing: In most cases, these installations require a large coverage area.

Experience has shown that an omnidirectional antenna mounted at 20 to 25 feet typically provides the best

overall coverage. Of course, this also depends upon the height of the racking, material on the rack, and

ability to locate the antenna at this height. Mounting the antenna higher will sometimes actually reduce

coverage, as the angle of radiation from the antenna is more outward than down. The antenna should

be placed in the center of the desired coverage cell and in an open area for best performance. In cases

where the radio unit will be located against a wall, a directional antenna such as a patch or Yagi can be

used for better penetration of the area. The coverage angle of the antenna will affect the coverage area.

●

Small office/small retail store: The standard dipole may provide adequate coverage in these areas

depending on the location of the radio device. However, in a back corner office a patch antenna may

provide better coverage. It can be mounted to the wall above most obstructions for best performance.

Coverage of this type antenna depends on the surrounding environment.

1 2 3 4 5 6 7 8 9 10 11 ... 87 88

No comments

Cisco AIR-ANT2420V-N= Datasheet Page 6