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or: How To Set Up a TWCN Node
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You'll eventually want to share on a larger scale. Let's say that again (say it out loud) ... you'll eventually want to share on a larger scale. Most wireless devices are geared towards the small office / home office (SoHo), and home user environments. As a result, a wireless signal typically propagates past your immediate house (especially if you live in Toronto, where many property lot sizes are about 20 feet in width). Picking up the signal with a good PCMCIA 802.11b card (such as Lucent's Orinoco series, undoubtedly the best card out there in many people's opinions) is easy on either adjoining property. If you wish to exceed that range you'll no doubt need an external antenna connected to your PCMCIA card for it to be of real use to you.
The internal antennas on PCMCIA cards are horrendous. They differ wildly between manufacturers, and they're often so inconsistent in reception and transmission (as the image below indicates) that rotating your card/laptop can change the signal strength dramatically. Many devices, such as Apple's Airport, may require you to do things like drilling holes and taking things apart to add extender antennas. For these reasons, manufacturers have now started building devices that provide for connections to external antennas; your best bet is to get one that does. Lucent is becoming an industry favourite for their Orinico series of cards (plus they have little connectors that allow you to attach to really large external antennas).
As you may well guess, some vendor's base units have better ranges than others. For an in-depth comparison of many popular brands, we recommend you read Network World's article "Putting 802.11b to the test" available at http://www.nwfusion.com/reviews/2001/0205rev.html.
There are two main categories of antennas: directional, and omni-directional (or non-directional). Directional antennas allow you focus their radiating power so you can shape the distribution pattern to best suite your application. Omni-directionals attempt to evenly distribute their radiating power, usually creating distribution patterns in the shape of spheres, or squished spheres.
Antennas are sometimes called aerials or repeaters, and they typically comprise an amplifier of some sort. Technically speaking, however, an antenna is just a electric conductor.
Antennas are essentially conductive materials that have an alternating current pass through them. This alternating current is a frequency measured in Hertz (cycles per second). When electricity passes through any conductor it loses some of its power to Electromagnetic Radiation (ER) which is sometimes referred to as electromagnetic propagation.
ER can be harmless, or harmful. The light from an incandescent bulb bouncing off of a wall an is ER, as is the light from the Sun; and they both are of a frequency that our eyes perceives as colours -- this is called the visible spectrum. We cannot see the entire spectrum of electromagnetic frequencies, in fact, we see but a tiny portion of it as the image below indicates. Harmful ER is naturally higher in energy, and thus higher in frequency that that of the visible spectrum. Regardless, rest assured that there is no harmful ER emitted by your wireless antenna.
As stated earlier, conductors lose energy; and some of that energy is transformed into ER. The higher the loss of power, the better the antenna, and the higher gain it is said to have. Gain is measured in bels, or more often, decibels (dB). It's an logarithmic scale of measurement, meaning 3 dB is about twice the power of 1 dB, 10 dB is 10 times the power, 13 dB is about 20 times the power, and 20 dB is 100 times the power. We will not go into the math behind the measurements in this document, but the general rule is: the higher the decibels, the better the signal. Sometimes you'll see dBi used, which is essentially a measurement for antenna gain, and at other times you'll see dBm and dBW used, which are the measurements of 1 mille-Watt, and 1 Watt of power amplification, respectively. Gain is a slightly misleading term for antennas, there is no actual gain in power or energy: you need amplifiers for that. The gain is a relative measurement of the difference between the ER for antennas with identical input power, or from the same antenna with differences in ER from one direction to another. As Tim Pozar of the Bay Area Wireless User Group puts it, "If you have an [directional] antenna that radiates better in one direction than another, it would have gain in this direction. The amount of gain would be shown as "dBi" or dB gain (or loss) over an isotropic antenna". If you're confused, just remember dBi is an relative measurement term for antennas, while dBm and dBW is a power measurement term.
The shape of the antenna affects its pattern of ER distribution. A straight wire is omni-directional. Meaning it goes in all directions pretty much evenly (ok, actually it's nowhere close to even in all directions let's pretend for now). Frequencies have wavelengths. Imagine a wave in a pond after you throw a pebble in, the length from the peak of one ripple to the peak of the next is its wavelength. The number of ripples generated in a period of one second is its frequency. Viewed from the top down, an omni radiates in the same pattern as those ripples in the pond.
You can change an antenna's length and shape to match wavelengths and/or their harmonics (which are whole number multiples or specific fractions of wavelengths) and thus increase its gain for both reception of a particular frequency, and the transmission of it. By altering an antenna's shape and length, you alter its potential to transmit and receive various frequencies with greater and lesser efficiency. That's the entire basis of antenna design.
You may find the following interesting if you want to learn more theory:
Undoubtedly you'll need to figure out what type of connector you have, so you can connect an antenna to your PCMCIA Card, amplifier, base station, or whatever else you have. As always, check your manufacturer's documentation for the specifics.
In the spirit of all things Internet, other's have done a good job of documenting the world of connectors (oh yes, I said world of connectors), so if you want to know more, visit the links below.
Connectors list by Rob Flickenger of the NoCAT Project:
http://nocat.net/connectors.html
HyperLink Technologies (of the USA) also has a good connectors page:
http://www.hyperlinktech.com/web/connectors.html
If the remainder of the appendix does not answer the question of which antenna is right for you, we recommend you take a look at Telex's very informative FAQ page at http://www.telexwireless.com/wlanfaq.htm.
Table of Contents | Previous Page | Next Page
Title: Wireless Network Access Point (WNAP) Set Up Guide, or: How To Set Up a TWCN Node
Authors: Jason Hammerschmidt (ffff654.noSPAM.at.yahoo.com), and Jason Ramsay-Brown
Contributors: Emir Alikadic, Hugh Reilly
Version: 1.0, April 2nd, 2002.
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