Nortel WLAN Security Switch 2361 Instalační příručka Strana 78
- Strana / 120
- Tabulka s obsahem
- KNIHY
Hodnocené. / 5. Na základě hodnocení zákazníků
78 Appendix
NN47250-506 (324883-B Rev 02 Version 02.02)
Antenna properties and considerations
In the design and installation of a WLAN system, system installers need to have some fundamental knowledge
of antenna performance and RF propagation characteristics to ensure efficient performance of the network.
This knowledge will assist these individuals with the proper selection of system antennas, as well as, guiding
their decisions on antenna mounting location and orientation in an effort to ensure optimum system coverage
and performance. A properly selected antenna system has the capability of improving overall system
performance and may lead to a reduction in system cost if the overall number of access points can be reduced.
Conversely, a poorly selected antenna system may degrade system performance and may lead to an increase in
overall system cost.
Antenna properties
The external antennas supported by the WLAN 2332 system are passive devices. A key attribute included in
their design is that they are DC-coupled to the output of the WLAN access point to enable the software to
detect their presence and direct the energy out their aperture rather than through the internal antennas mounted
within the access point housing. Since they are passive devices, they do not process nor amplify the RF signal.
Even if they are 100% efficient, they cannot radiate more total power than is delivered to their input terminal
from the access point.
The basic properties that are used to describe the performance of an antenna include impedance and VSWR
(Voltage Standing Wave Ratio), radiation patterns, 3-dB beamwidth, directivity, gain, EIRP (Effective
Isotropic Radiated Power), polarization and bandwidth. These properties and their impact on system
performance are discussed in the following sections.
Impedance and VSWR
In order to achieve maximum power transfer between an access point and an antenna, the input impedance of
the antenna must identically match the characteristic impedance of the output of the access point. If the two
impedances do not match, a reflected wave will be created at the antenna input and travel back towards the
access point. This reflection is associated with a mismatch loss between the access point and the antenna and
results in an overall reduction of system efficiency and available transmission power. The WLAN supported
external antennas have been designed to match the output impedance of the WLAN Series 2332 access points
to ensure optimum system power transfer.
The Voltage Standing Wave Ratio or VSWR is the ratio between the maximum voltage and the minimum
voltage that appears along the transmission line connecting the access point to the antenna. The VSWR, which
can be derived from the level of reflected and forward waves, is also an indication of how closely or efficiently
an antenna's input impedance is matched to the characteristic impedance of the cabling and output impedance
of the access point. An increase in VSWR indicates an increase in the mismatch between the antenna and the
access point. These increases can be a direct result of corrosion, damaged cables, loose connections or seals
and lengthy cable extensions from the access point. All of these concerns must be checked and optimized
during the installation of the antenna system by the professional installer.
To indicate how increased VSWR impacts overall system performance, the table below details the percentage
of power reflected by the antenna, and the resultant overall transmission loss, for several typical VSWR values.
For a 1.5:1 VSWR, the transmission loss is approximately 0.2 dB or a 4.0% reduction in efficiency.
- Solution Guide 1
- Contents 3
- 6 Contents 6
- Outdoor Solution 7
- Customer service 8
- 2332 Access Points 9
- Canadian IC statement 10
- Declaration of conformity 11
- Радио Модел 12
- Community 14
- Transmit Power Control (TPC) 15
- Taiwan Compliance Statement 16
- United States and Canada 18
- 2.4 GHz Band 18
- 5.0 GHz Bands 18
- External Antenna Statement 22
- Country 2.4 GHz 5.0 GHz 23
- Warning conventions 27
- Radio safety warnings 29
- Earth ground warning 35
- Introduction 39
- Package contents 40
- Signal path distance 41
- Antenna polarization 41
- Signal path clearance 41
- Physical site survey 41
- Physical site 42
- Hardware installation 43
- Installation 47
- Grounding principles 48
- Figure 6. Drip Loops 49
- Outdoor external antennas 50
- Coax cable seal installation 51
- Software installation 53
- Site Planning 58
- Safety Precautions 59
- Reference Information 60
- Applying coax seal tape 61
- Figure 14. Mounting Bracket 62
- Terminal Strip Connection 66
- Software 67
- Appendix 69
- Surge Suppression 70
- Appendix 75 75
- 76 Appendix 76
- Appendix 77 77
- Antenna properties 78
- Appendix 79 79
- Effective Radiated Power 80
- Polarization 80
- RF Propagation and Path Loss 82
- Appendix 83 83
- 84 Appendix 84
- Appendix 85 85
- 5.15 GHz 86
- 5.47 GHz 86
- 5.85 GHz 86
- 88 Appendix 88
- Appendix 91 91
- 92 Appendix 92
- Appendix 93 93
- 94 Appendix 94
- Appendix 95 95
- 96 Appendix 96
- Appendix 97 97
- 98 Appendix 98
- Appendix 99 99
- 100 Appendix 100
- Appendix 101 101
- 102 Appendix 102
- Appendix 103 103
- 104 Appendix 104
- 2462 MHz 105
- 2412 MHz 105
- 2437 MHz 105
- 106 Appendix 106
- Appendix 107 107
- 108 Appendix 108
- Appendix 109 109
- 110 Appendix 110
- Appendix 111 111
- 112 Appendix 112
- Appendix 113 113
- 114 Appendix 114
- Appendix 115 115
- 116 Appendix 116
- Appendix 117 117
- 118 Appendix 118
- Appendix 119 119
- Figure 23. Top view 119
- Figure 24. Bottom view 119
- 120 Appendix 120
- Figure 25. Side view 120
- Figure 26. Mounting screws 120
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