Range

You will see specifications for different brands of wireless networking devices quoting wildly different ranges. Take these claims of huge range with a pinch of salt. Unless the manufacturers have got something very wrong, or are operating at illegal power output levels, then products from different sources will behave much the same within similar parameters. Any variations in the true range between products, assuming the comparison is done with products running at similar power levels, comes down to factors such as antenna gain (different gain alters beam spread and also alters the affective receive sensitivity), receive sensitivity, and (particularly for indoor use) the ability to cope with multi-path reflection affects.

There are two types of application in which wireless networking is used: internal and inter-building.

Indoors
Radio waves travel in straight lines and at 2.4GHz do not penetrate obstacles very well. Some surfaces reflect the signals quite well whilst others tend to absorb them. Water, which comprises most of you , is particularly good at absorbing the energy, so you will find that putting your hand over an antenna can reduce the signal substantially. (Your hand won't warm up because output power is limited to 100mW in Europe - well below the power output of your mobile phone!). 5GHz wireless suffers from similar problems BUT, with better penetration and scatter, it can give improved non-line-of-site (NLOS) capabilities over 2.4GHz devices.

As a general rule 802.11b/g devices will usually cover a house quite well but there are no guarantees. You might also find, particularly for 11g, that the connection speeds will drop in order to get a reliable link. In fact, often an 11g product with up to 54meg potential will give similar performance to an old 11b device even though 11b is only up to 11meg speed. The signal passes better through wooden floors and ceilings than through brick walls, and has no chance at all through concrete or stone. The use of an access point in the loft connected to a directional antenna pointing down from the rafters has proved an effective way to get full coverage in a typical house. For a more restrictive range the built-in antennas often work very well.

Your choice of wireless network adapter may be significant. If your mini tower PC stands on the floor with it's back to a radiator, you can't a expect built-in adapter with integral aerial to work very well. Or if you tend to sit with your notebooks aerial sticking out of the left hand side and your access point is down the corridor to your right, then the computer itself will screen the signal. Try an adapter with an external aerial that can see over your keyboard.
See our 'Wireless Around the Home' article for a more in depth discussion on using 2.4GHz wireless in buildings

802.11a/5GHz radio, although costing a little more than 2.4GHz products, has much better penetration and scatter making it better for indoors operation where it needs to reach remote rooms. In our opinion, especially with 11n technology, 5GHz is the future for wireless networking in buildings (mind you we’ve been saying that for years now and still waiting for it to take over from 2.4GHz products!)

You can read more information on 5GHz wireless in our '5GHz Frequency Bands' Article.

Outdoors
The following table is a guide to the distances you might expect to achieve using 'off-the-shelf' wireless devices a standard 100mW access point with a given antenna gain at both ends . A receiver sensitivity of about -83dB is assumed.

Antenna Gain
Q. How does an antenna produce gain?
A. By focusing the available radio energy in one direction.
Q. OK, so how can an 'omni-directional' antenna have gain?
A. Because it radiates around itself in a disc pattern, stealing power from above and below.
The above Q&As should help you get a feel for the radiation pattern for different types of antennas. A 0dB antenna radiates equally over a complete sphere. Bearing in mind that 3dB represents a doubling of radiated power, you could imagine a 3dB directional antenna radiating its signal into one half of that sphere. A 3dB omni-directional antenna would have a radiation pattern in the shape of a sphere with a cone removed from the top and bottom.

Diversity Receivers
Wireless signals (both 2.4GHz and, to a much greater extent, 5GHz) reflect readily off many surfaces, there will often be a pattern of patches around the room where reflected signals cancel out the direct signals leading to 'dead zones'. If your antenna is in such a dead zone you get no signal. However, for every dead zone there will be a 'double-power' zone. Due to the shortness of the radio waves at these high frequencies then the distance between a good patch and a bad patch can be only a few centimetres Wouldn't it be nice if you could have a second antenna, just a few centimetres away? Then, there would be a good chance of this second antenna sitting in a better reception zone.
A system with two aerials in this arrangement is called a diversity receiver. Many wireless devices use diversity receivers to try and improve NLOS operation. Of course, 11n technology with multiple antenna and data streams is really a super version of diversity – this is one of the reasons why 11n is theoretically better for indoor/non-line-of-site operation.
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