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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/
This site shows what's commercially available, but gives no price. Does any fellow slashdotter have a clue about exactly how much money has been saved?
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distract free online advertising
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
The most likely shortcoming is that it probably violates the FCC rules about how much power an unlicensed transmitter can put out.
No, the total output power hasn't changed. The antenna just concentrates the signal into one direction.
The FCC doesn't restrict what kind of antenna you can use, just the power going into the antenna.
What, you mean like Athens Metropolitan Network?
Very cool i would say...
At take a look at the node count
To these people it's very usefull.
Slashdot Sig. version 0.1alpha. Use at your own risk.
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
It's still illegal to have too much gain. Concentrating the power increases the signal strength (which in effect is increasing the power).
I use a Netgar MA111 USB wireless key in my Linux router. You need linux-wlan-ng, which provides the proper usb_prism2 drivers (and of course, working usb hardware).
Works pretty dang well, probably better than the Windows setup.
BAM!
I've got one based on the atmel (at76c503_rfmd). It works pretty well. My only gripe is that even though it is open source, it isn't currently in the kernel so I have to recompile before every kernel upgrade.
I've been using it to access my server at home because I'm too lazy to lay cable under the house.
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 don't believe directionals are illegal.. there are still rules for how to deal wiht it.. it's just not as liberal as in the US.
Generally it's something like 3db of gain is permitted for each 1db drop in transmitter power.
So you can't just start throwing directionals off your 100mW transmitter.. you also have to attenuate it properly first.
This allows you to get directional gains, but keeps a sane limit on the total power.
Snipped from some site:
The FCC regulations for Point to Multi-Point allows only 36 dBm (4 watts) EIRP. This is 30 dBm (1 watt) into a 6 dBi antenna. If you use a 10 dBi wireless antenna, you must limit your transmitter (or amplifier) to 26 dBm (10 + 26 = 36 dBm). For a 14 dBi panel wireless antenna, this allows a 22 dBm transmitter (or amplifier).
According to FCC regulations, 2.4 GHz Part 15.247 point-to-point transmitters may use a 30 dBm transmitter with a 6 dBi antenna. For a 3 dB increase in antenna gain, the transmitter power output must be reduced by 1 dB.
My comments below:
In Canada:
The maximum EIRP is 4 Watts for both point-to-point and multi-point networks with a maximum of 1 watt from the transmitter.
Meaning:
In the US, Point to point links have a distinct advantage.
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.
"wa-la?" I believe thats "voila"
I read the internet for the articles.
As cool as this antenna is, it isn't very expensive to buy a nice prebuilt wireless antenna these days. Pacific Wireless dishes, for example, are about US$50 for 19dBi or $70 for 24dBi. I've used their products, and they are very nice. I've given up on building 802.11 antennas: it's too much work vs the cheap commercial antennas for me.
Nice point about the modularity, but if you did want to swap 802.11b for a 802.11a transciever you'd need to change the design as the frequency (and hence wavelength) is different.
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 :-)
I was involved with the installation and testing of the woktenna. This is the dish style antenna on the wifi site (I took the picture of it on the pole on the roof), NOT the skimmer one. I note the author of that site has made his own woktenna since. I have also got other close up pictures of it (if they are needed). Three other miscreants are involved with this plot :)
A few stats:
The antenna has a biquad element mounted at the focal point of the dish, and the biquad element does not have the backplane reflector installed; just the 'bow-tie'. It is soldered directly to the cable connector via copper tubing, which is mounted in a hole at the back of the wok.
The distance this is currently working at is around 4 or 5 kilometers (have not tested further yet). Connections are a uniform 11mbit, and throughput (FTP) to the acess point FTP is 600 kilobytes a second or more. Ping times of less than 5ms. Netstumbler reports a SNR of around 27, signal strength at the AP is around -90dB. The wifi card in use is a Dick Smiths (www.dse.co.nz) xh8135. IIRC, some 35mW.
Previous aerials at the site included a ~15 - ~17dB BiQuad, and a Helical of simular gain mounted around 2 meters up from the roof of the house, and some 10 meters of 0.1dB/meter loss coax. The sigal with the helical was unusable - often dropping out. The Biquad was better, but only providing about 30k/sec throughput (signal strength about -98 - -99dB).
The Wok was fantastically better.
*I* currently use a short helical, and am perhaps 2km from the AP; I get maybe 550k/sec throughput. Both of us have line of sight.
We are all part of the wifi proto-network at http://www.oamaruwireless.com.