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4km WiFi Range w/ $5 DIY Antenna
Mignon writes "This industrious fellow in New Zealand made his own WiFi antenna using a USB WiFi adapter and a Chinese 'spider skimmer mesh scoop.' He got about 17 dB signal improvement for about US $5 in materials." Update: 05/25 23:09 GMT by T : Reader
John Stockdale offers a U.S. hosted mirror of the site. Update: 05/26 13:58 GMT by T : Reader Jared Mauch contributes another mirror.
If it was omni-directional, then I'll be very impressed, but you can make a pringles antenna for very cheap, and get about 10 miles range (line of sight).
The best way to predict the future is to invent it. -Alan Kay
There was a story about freecache, but no one here on slashdot ever uses it in stories. Here's a pre-cached link, in case the main NZ server goes up in smoke. http://www.freecache.org/http://www.usbwifi.orcon. net.nz/
http://www.stanford.edu/~jstockdl/tmp/usbwifi.orco n.net.nz/
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Mirrored as much as I could of the images before the server was smoked.
-S
**AA: a bunch of mindless jerks who'll be the first against the wall when the revolution comes
In theory for a transmitting antenna, there is no limit to how much gain you can get. Gain is the ratio of received power to the power you would get with an isotropic radiator. To get gain, you just focus the beam tighter. The limit to how tight you can focus the beam is set by the aperture of the antenna. The gain of a receiving antenna is set by its effective area. Gain isn't hard to get.
The bigger problem is to get line of sight. At this frequency, if you can't get line of sight, all the gain in the world won't help.
The super cantenna is only 12 db. 17 is more impressive, and should result in greater range.
Range itself is hard to compare, as it depends on environment, the radios used (cheap 35 mW? 200 mW with good receive sensitivity?), whether the same antenna is used on both ends, and the subjective evaluation of what exactly constitutes a "useable signal".
-jim
Also, to those confused about how antenna gain works. The gain is measured in comparison to the output of an isotropic radiator, basically something that puts out the same signal strength in all directions. So that means that any unamped antenna with a gain higher than 1dBi is directional in some sense, because the total radiated power is still the same. So-called omnidirectional antennas really are only omnidirectional in the horizontal plane, if you go up or down their signal strength drops off rapidly.
IIRC, the maximum tx power in the 2.4ghz band for unlicensed users is 1 watt, or 4 watts EIRP. For point-to-point links, though, you can trade 1db of power reduction for 3 db of antenna gain, allowing much higher EIRP.
More info is here
-jim
The device is putting out the radiation... No matter antenna you put on it you don't increase the output of the device. Now you do focus it into a much "hotter" spot when you make it directional. Even so though none of these devices are allowed to excede 1W of effective radiated power (No commercial consumer device currently excedes 250mw).
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To give you an example... You microwave uses 4000 times that much power to cook food with.
I would imagine if you stood in the beam path of a 20+db antenna for a couple months you would have health issues... but you also wouldn't have a signal
As health risks go a cell phone is a MUCH larger output of power and you stick it right next to your head. Worry about those first
And FWIW cantennas are no better... most directional antennas send most of their power out the front but all of them have sidelobes.
Telcos have alot of dark fibre in the States. Most people assume that's optical fibre...but it's actually moral fibre.
I didn't shop around for best price, etc, etc, 'cos I knew that once this thing hit slashdot, there was gonna be a worldwide stockout on the chinese cookware. I could have gotten things a bit cheaper if I had shopped around, but short of an AUD$1200+ aeroplane ticket to Guangzhou and buying direct from manufacturers, there was no way this setup would cost $5.00 of anyone's money. With time and petrol and driving around, I guess it cost AUD$100.00. Good fun tho, and worth every cent.
I find your ideas intriguing and I wish to subscribe to your newsletter.
There's nothing stopping you (if you leave out the legal), but it wouldn't be all that useful. While an amplifier would boost your output, it will do nearly nothing to increase the signal that you recieve i.e. you will be speaking louder but the person talking to you will still be speaking at the same volume. You may well ask then how an antenna's gain works out overall then, as you are still basically just boosting the wattage of your signal, not the other guy's. The answer there comes from the directionality of the antenna - while the other guy isn't speaking any louder the directional antenna allows you to filter out the noise coming from everywhere else, making it easier to hear what he's saying. Thus with a directional antenna, you're getting two good effects, while with the amp you're really only getting one. Now, OTOH, if you stuck an amp on your rig AND the other guy's rig, then you'd be talking :-)