Download (direct link):
647.) This product, which you can buy online for about 820, provides you with a remote stand for a regular or high gain SMA antenna (Linksys also offers a model for TNC antennas). You do lose some of your signal strength by running the signal over a cable to this remote antenna, but in many cases you gain more in improved signal path (less path loss) than you lose in the transmission path.
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Some common types of directional antennas include
Patch or sector antennas: These are the least “extreme” of the directional antennas, offering a sector that’s as much as 180 degrees in a compact antenna that looks a lot like an omnidirectional that’s been flattened out a bit. Patch or sector antennas can be helpful within a home or office when you just need a little extra help reaching the AP.
Yagi antennas: We just love saying “Yagi.” Yagi antennas are highly directional antennas that look sort of like the TV antenna you had in the attic as a kid (or at least like the one Pat had in his attic). They are hard to describe, so check out Figure 7-5 to see one in all its Yagi glory. Yagis are particularly good for outdoor, point-to-point applications, and not quite as good for general use indoors.
Parabolic antennas: Even more directional are the parabolic antennas. These devices look like the “dishes” used to pick up satellite TV, and share similar design philosophies. You probably won’t ever use a parabolic antenna in your network unless you’re trying to shoot a signal across the country many miles.
Waveguide: Have you heard of the Pringles can Wi-Fi antenna? This famous hack involves putting a waveguide antenna (an antenna that focuses the radio waves from your Wi-Fi system) inside a Pringles potato chip can. You can find a commercial version of this concept at http:// shop.netstumbler.com/detail.aspx?ID=288.
When would you use a directional antenna if you’re not building a point-to-point outdoor network? Typically, we recommend an omnidirectional antenna on your main AP (you may wish to upgrade your AP’s antenna to a higher gain omnidirectional). Directional antennas come in handy on remote wireless stations in your home or office.
Can’t reach the east wing of the house? Try a patch antenna or even a Yagi. Got trouble with the home office over the garage? See if a sector antenna helps. Our general rule of thumb is to stick with an omnidirectional for the AP and go with directionals where needed at the edge of your network.
Feel free to break this rule if the layout of your home or office dictates that your AP is not physically near the center of your space. If your AP is going in the home office in a corner of the house, feel free to try a sector or patch antenna that focuses your signal over 180 degrees and effectively covers the rest of the house better than an omnidirectional antenna would.
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Recall the formula we mentioned earlier in the chapter for received signal strength, in the section called “Antennas for All”? One element of this formula was the transmit power. Antennas don’t actually boost this power — at best, a high gain antenna directs more of this power in a particular direction, increasing the effective signal strength.
But in some situations, you need to start off with a little extra juice to begin with — meaning you want to increase the transmit power itself. To do this, you need to add a device known as a signal amplifier or signal booster.
These devices simply add an amplifier to the signal path between your Wi-Fi device and the antenna. This amplifier (like the amplifier in your home stereo, for example) simply increases the power level of a signal, hopefully with a minimum of increased noise and distortion.
A signal booster can have two components:
A transmit booster: This increases the outgoing signal level by amplifying the signal before it hits the antenna.
A receive booster: This increases the incoming signal level by amplifying it after it has been received by the antenna.
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Most (legal) boosters transmit at about 500 mWatts (a half a Watt) of power, whereas the APs themselves transmit at one tenth (or less) of that amount.
Installation varies by unit, but most signal boosters are simple plug-in replacements for an existing antenna. For example, the RadioLabs 2.4Ghz Wireless Range Extender (www.radiolabs.com/products/wireless/ wireless-range-extender.php, $119.95) plugs into any AP using an RP-SMA or RP-TMC connector and provides an instant power boost in both directions. Figure 7-6 shows this unit.
Boosters provide you with the most benefit on the transmit side of things — making it easier to pick up signals at greater distances. On the receive side of things, they do indeed “boost” the signal that’s being picked up, but they don’t improve the quality of the signal. If a signal is really noisy, the noise (as well as the signal itself) is also boosted — so you may not get a great increase in quality and speed.