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Wireless Networking

Revision as of 18:37, 25 March 2007 by Brodiepearce (Talk | contribs)

Linksys WRT54GS wireless router
18dBi Conifer, horizontally polarised
slotted waveguides

Contents

Wireless Standards

802.11b 
provides speeds upto 11Mbps at 2.4GHz
802.11g 
provides speeds upto 54Mbps at 2.4GHz
802.11a 
provides speeds upto 54Mbps at 5.8 GHz
802.11n 
an unratified standard that should provide speeds of upto 100Mbps (WWiSE and MIMO are two competing proposals for 802.11n)

Wireless Concepts

LOS 
Line-of-sight; if two locations have a clear, unobstructed view of each other, they are said to have good LOS. Because microwave energy is absorbed by solid obstructions, LOS is required for a good wireless signal between two locations.
Beamwidth 
The beamwidth of an antenna is the angle between the half-power (3 dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe, usually expressed in degrees (and usually given in the horizontal plane).
Bandwidth 
the amount of data that can be transferred in a given time period, normally measured in kbps (kilobits per second) or Mbps (megabits per second).
Frequency 
The number of cycles per second. The frequency of 802.11b ranges from 2.412 GHz (channel 1) to 2.477 GHz (channel 14).
Gain 
In antenna design, gain is the logarithm of the ratio of the antenna's radiation pattern to that of some ideal antenna, typically the theoretical isotropic antenna.
dB 
a measure of the ratio between two quantities, and commonly used to measure signal-to-noise ratios.
SNR 
Signal-to-noise ratio is the power ratio of the signal (meaningful data) and the background noise.

Wireless Security

Please see Wireless Network Security.

Antennas

If you want to improve the range of the standard "rubber-ducky" antenna(s) on your wireless AP/router, before spending money on a higher gain antenna, try making some simple reflectors for the standard antenna, as detailed on the deep Dish Cylindrical Parabolic Template website.

Antenna Types

Omni-directional 
radiates a signal in multiple directions, typically 90, 180 or 360 degrees.
Directional 
typically focuses the signal in a single direction.

Omni-directional antennas are typically used in situations where multiple clients will be connecting, from multiple directions. A directional antenna is preferred for point-to-point links, as the signal is focussed in the direction you want, rather than being dispersed in multiple directions. Noise is also reduced, and you're also reducing the amount of RF "pollution".

Antenna Polarisation

Polarisation is defined as the orientation of the electric field of an electromagnetic wave. Two often used special cases of elliptical polarization are linear polarization and circular polarization. The initial polarization of a radio wave is determined by the antenna that launches the waves into space.

Linear Polarisation 
the electric field vector stays in the same plane
Circular Polarisation 
the electric field vector appears to be rotating with a circular motion about the direction of propagation (can be either right-hand or left-hand rotation)

The Helical antenna is circularly polarised, while all other antennas listed below are linearly polarised, with the linear polarisation being either vertical or horizontal, depending how the antenna is oriented.

Homebrew Antennas

The majority of the antennas listed below can be constructed at home with tools that most people will have in their shed.

Cantenna

Biquad

Dishes

Helical

Collinear

Slotted Waveguide

Patch Antenna

Discone

other Omni Antennas

Community Networks

Most major cities have a community wireless network (aka freenet), consisting of like-minded individuals who have established a wireless network between their houses and other elevated places with good LOS.

If you're interested in getting involved, contact your local freenet for more help and assistance.

ACT

New South Wales

Northern Territory

Queensland

South Australia

Tasmania

Victoria

Western Australia


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