Cisco Cisco Aironet 350 Wireless Bridge Guía Para Resolver Problemas
Omnidirectional antennas (which provide 360 degree coverage)
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Directional antennas (which provide a limited range of coverage)
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Antenna Gain
Antenna Gain is measured in dBi and dBd (0 dBd = 2.14 dBi). If the gain of the antenna goes up, the
width of the coverage area that antenna provides goes down. Coverage areas or radiation patterns are
measured in degrees. These angles are referred to as beam width and they have horizontal and vertical
measurements. Wider angles mean wider coverage, while smaller angles (typically with higher gain)
mean more coverage. In most installations, antennas should be installed in a vertical polarization
(antenna perpendicular to the ground).
width of the coverage area that antenna provides goes down. Coverage areas or radiation patterns are
measured in degrees. These angles are referred to as beam width and they have horizontal and vertical
measurements. Wider angles mean wider coverage, while smaller angles (typically with higher gain)
mean more coverage. In most installations, antennas should be installed in a vertical polarization
(antenna perpendicular to the ground).
The range of powers, voltages, and currents encountered in radio engineering is too broad to be
expressed on a linear scale. Consequently, a logarithmic scale based on the decibels (dB, one tenth of
a bel) is used. Decibels do not specify a magnitude of a power, voltage, or current, but rather, a ratio
between two values of them. The unit dBm is a power level relative to 1 milliwatt (mW). An
important relationship to remember is:
expressed on a linear scale. Consequently, a logarithmic scale based on the decibels (dB, one tenth of
a bel) is used. Decibels do not specify a magnitude of a power, voltage, or current, but rather, a ratio
between two values of them. The unit dBm is a power level relative to 1 milliwatt (mW). An
important relationship to remember is:
0 dBm = 1 mW Power (dBm) = 10 log (power in mW/1 mW)
For example, if an amplifier has an output of 20 W, its output in dBm would be 43 dBm:
Power (dBm) = 10 Log (20000/1) = + 43 dBm
If a high−gain omnidirectional antenna is used, make sure that it is mounted at a correct height. The
omnidirectional antenna radiates the signal in a donut shape around the tip of the antenna. If the
antenna is not mounted correctly, it is possible that the signal could pass over the target receiver
antenna.
omnidirectional antenna radiates the signal in a donut shape around the tip of the antenna. If the
antenna is not mounted correctly, it is possible that the signal could pass over the target receiver
antenna.
For more information on this topic, refer to RF Power Values.
4.
Antenna Placement
Poor antenna placement (such as duct taped to a metal object) can cause many problems. Make sure
that the antenna support structure is solid. An example of a poor antenna support structure would be
one mounted on a pole that waves back and forth in the wind. Make sure that the antenna mounting is
weather proof. Cisco Aironet Bridges are not designed to be subjected to weather unless contained in
an enclosure. Be sure that there is no water in or on the antenna cable, and that the antenna cable is
grounded. Antenna cables are not designed to protect network devices from static electricity or
lightning surges that travel on coaxial transmission lines.
that the antenna support structure is solid. An example of a poor antenna support structure would be
one mounted on a pole that waves back and forth in the wind. Make sure that the antenna mounting is
weather proof. Cisco Aironet Bridges are not designed to be subjected to weather unless contained in
an enclosure. Be sure that there is no water in or on the antenna cable, and that the antenna cable is
grounded. Antenna cables are not designed to protect network devices from static electricity or
lightning surges that travel on coaxial transmission lines.
5.
Antenna Alignment Tool and Carrier Test
It is very important to point the antenna in the right direction. Cisco has a light duty tool, the antenna
alignment tool, built into the bridge operating system that helps align the antenna in the correct
direction. A carrier busy test is also provided to help to avoid RF interference and to find out which
channel is less busy.
alignment tool, built into the bridge operating system that helps align the antenna in the correct
direction. A carrier busy test is also provided to help to avoid RF interference and to find out which
channel is less busy.
6.
Transmission Line
Avoid use of long, coaxial antenna cables. The longer the cable, the higher the signal loss over that
cable. RF energy is carried between the antennas and the radio equipment through coaxial cable.
Actual decibel loss depends on the type of cable chosen, but Cisco low−loss cable encounters
approximately 6 dB for every 100 feet of cable. Loss occurs on both transmitted and received signals.
If the cable diameter is larger, loss is decreased, but thicker cable is more costly. Make sure that the
cable is not crimped in any way. Finally, as the transmitted frequency (channel) increases, so does
signal loss.
cable. RF energy is carried between the antennas and the radio equipment through coaxial cable.
Actual decibel loss depends on the type of cable chosen, but Cisco low−loss cable encounters
approximately 6 dB for every 100 feet of cable. Loss occurs on both transmitted and received signals.
If the cable diameter is larger, loss is decreased, but thicker cable is more costly. Make sure that the
cable is not crimped in any way. Finally, as the transmitted frequency (channel) increases, so does
signal loss.
7.
If the signal passes through glass, metallic tint on the glass can degrade the signal.
8.