Appendix C Wireless LANs
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Antenna Overview
An antenna couples RF signals onto air. A transmitter within a wireless device sends an RF
signal to the antenna, which propagates the signal through the air. The antenna also operates in
reverse by capturing RF signals from the air.
Positioning the antennas properly increases the range and coverage area of a wireless LAN.
Antenna Characteristics
Frequency
An antenna in the frequency of 2.4GHz (IEEE 802.11b and IEEE 802.11g) or 5GHz (IEEE
802.11a) is needed to communicate efficiently in a wireless LAN
Radiation Pattern
A radiation pattern is a diagram that allows you to visualize the shape of the antenna’s
coverage area.
Antenna Gain
Antenna gain, measured in dB (decibel), is the increase in coverage within the RF beam width.
Higher antenna gain improves the range of the signal for better communications.
For an indoor site, each 1 dB increase in antenna gain results in a range increase of
approximately 2.5%. For an unobstructed outdoor site, each 1dB increase in gain results in a
range increase of approximately 5%. Actual results may vary depending on the network
environment.
Antenna gain is sometimes specified in dBi, which is how much the antenna increases the
signal power compared to using an isotropic antenna. An isotropic antenna is a theoretical
perfect antenna that sends out radio signals equally well in all directions. dBi represents the
true gain that the antenna provides.
Types of Antennas for WLAN
There are two types of antennas used for wireless LAN applications.
• Omni-directional antennas send the RF signal out in all directions on a horizontal plane.
The coverage area is torus-shaped (like a donut) which makes these antennas ideal for a
room environment. With a wide coverage area, it is possible to make circular overlapping
coverage areas with multiple access points.
• Directional antennas concentrate the RF signal in a beam, like a flashlight does with the
light from its bulb. The angle of the beam determines the width of the coverage pattern.
Angles typically range from 20 degrees (very directional) to 120 degrees (less directional).
Directional antennas are ideal for hallways and outdoor point-to-point applications.
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Страница 59: ...59 PART II Network Wireless LAN 61 WAN 69 LAN 77 DHCP 79 NAT and Firewall WAN to LAN 81 DDNS 89 ...
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Страница 100: ...Chapter 13 Access Control NBG 510S User s Guide 100 ...
Страница 103: ...103 PART IV Management UPnP 105 Static Route 113 ...
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Страница 116: ...Chapter 16 Static Route NBG 510S User s Guide 116 ...
Страница 117: ...117 PART V Maintenance System 119 Logs 123 Tools 125 ...
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Страница 136: ...Chapter 20 Secure Remote Access Title NBG 510S User s Guide 136 ...
Страница 140: ...Chapter 21 Secure Remote Access User Info NBG 510S User s Guide 140 ...
Страница 150: ...Chapter 23 Manage User Access Permissions NBG 510S User s Guide 150 ...
Страница 154: ...Chapter 24 Secure Remote Desktop Control NBG 510S User s Guide 154 ...
Страница 162: ...Chapter 25 Secure Remote Access Screens NBG 510S User s Guide 162 ...
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Страница 170: ...Chapter 26 Troubleshooting NBG 510S User s Guide 170 ...
Страница 176: ...Appendix A Product Specifications NBG 510S User s Guide 176 ...
Страница 180: ...Appendix B Common Services NBG 510S User s Guide 180 ...
Страница 198: ...Appendix D Legal Information NBG 510S User s Guide 198 ...
Страница 204: ...Appendix E Customer Support NBG 510S User s Guide 204 ...
Страница 209: ...Index NBG 510S User s Guide 209 WPA PSK 189 190 application example 191 ...
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