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> Homemade Wifi Antennas
Fallingwater
Posted: August 23, 2008 01:27 pm
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This xkcd comic, and its forum thread, have piqued my curiosity.

I knew about cantennas, but I never bothered making one. Now I'd like to try, but I have one question.
It's quite hard to believe that a pringles can is the most efficient way to make an antenna. What do you guys think is the best directional wifi antenna that can be made with generally available parts? Perhaps a satellite dish with a USB receiver stuck in the center would work better? (just guessing here.)


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JoOngle
Posted: August 23, 2008 01:39 pm
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Yes it works. Be aware though - Some countries have laws against
using other peoples network even if unencrypted, and some take
it very seriously - you COULD leave your IP adress, MAC adress etc.
that could eventually identify you - not likely - but it has happened.

Now thatīs said...

I have a HUGE "pringles" can...actually itīs the internal-trash can
of my "Bullet style" Trashcan...it is a HUGE oversized pringles can
and I placed my iPod touch inside it (had to push it back and forward
inside the can in order to find the sweet-spot) but it immediately
registered 30-40 networks as opposed to 3-7 ...so yeah...it works!


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CWB
Posted: August 23, 2008 01:46 pm
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yep ...

like an old boy told me years ago : "if you can't hear 'em you can't work 'em" .

i used a piece of foil mounted on the wall behind my wireless card antenna and improved my link signal from marginal to 75% .


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Jimthecopierwrench
Posted: August 23, 2008 03:42 pm
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Beats me. Pringles cans here are cardboard tubes (with a metal disc on one end and a ring on the other) and don't seem to correlate dimensionally close with any even fractions of wavelength so i'm not really sure why they'd shine above a piece of wire.

One guy was using 4" dia. metal juice/coffee cans. Although I'd expect the ridges stamped into the can would offer some attenuation I'd still think it'd be way superior to pringles.

Why not try cardboard, hot glue, and tinfoil until you've come up with satisfactory dimensions and them maybe transfer them to sheetmetal? Maybe start wih mounting the element 1/4 wave from the rear reflector in a 1/2W dia, 2W long tube?

Seems to me That you'd almost need a detector of some sort with a real signal strength output (not the stupid bars in the corner of your screen - mine at least seem to represent nothing useful) to experiment with your designs, else you'r guessing or following someone else's diagrams. With the price of dongles being so cheap now i wonder it there is any front end in them that could be hacked at to make such a detector?





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Thunderbolt
Posted: August 23, 2008 04:22 pm
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QUOTE (Jimthecopierwrench @ August 24, 2008 12:42 am)
Beats me. Pringles cans here are cardboard tubes (with a metal disc on one end and a ring on the other) and don't seem to correlate dimensionally close with any even fractions of wavelength so i'm not really sure why they'd shine above a piece of wire.

I'm guessing it's focusing a weaker omni-directional signal to a more powerful directional transmission.

QUOTE
This xkcd comic, and its forum thread, have piqued my curiosity.

This'll make you orgasm. laugh.gif
http://www.usbwifi.orconhosting.net.nz/

About the most efficient home made Wi-Fi antenna you can make is a biquad antenna. Costs a bit more and takes a bit more to make but it'll be a helluva lot better than a Pringles can. biggrin.gif


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CWB
Posted: August 23, 2008 09:50 pm
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pringles cans are cardboard/aluminum foil laminates .

usually , the more gain that an antenna has , the narrower the beamwidth and greater the directionality (eg : front to back ratio in a yagi) .

it is surprising what happens at microwave frequencies ... multiples of wavelengths become small and consequently phase addition and cancellation points can be found with relatively small increments in dimensions and spacing .

strange looking antennas ? the old uhf "bowtie" arrays and the steerable helical plane arrays (bed-spring) .


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tekwiz
Posted: August 23, 2008 10:18 pm
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QUOTE (Changes @ August 23, 2008 04:27 am)
Perhaps a satellite dish with a USB receiver stuck in the center would work better? (just guessing here.)

It certainly would, although you want it in the focus, which isn't necessarily the center of most sat dishes.
Antenna gain is fairly easy to understand, when you remember that microwaves act very much like light. An omnidirectional, unity gain antenna radiates(& receives) very much like a candle flame...in a spherical pattern. Any reflector scheme, from a basic plane, to a parabolic dish, will increase the amount of light going in a given direction; at the expense of light going in all other directions. The tighter the beam, the further it will go. It's as simple as that. The cantenna works by concentrating all of the radiation more or less in a single direction. A dish, being a more coherent reflector, produces a tighter, better organized beam, which translates into more range. Since you can't get something for nothing, this comes at the price of requiring much more accurate antenna positioning toward the signal source, as a highly directional antenna won't pick anything up except what it is directly pointed at. cool.gif


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Fallingwater
Posted: August 24, 2008 12:20 am
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Just how directional would a satellite dish antenna be? Are we talking "gets just the one AP it's pointed at with a margin of 10 centimetres" or "a building two hundred metres away"?

Also: am I right in thinking the focus of a satellite dish is usually where the receiver doodad sits on its stalk? If that's the case all I have to do is put a usb wifi dongle on the stalk in place of the receiver, right?


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Nothing40
Posted: August 24, 2008 12:39 am
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I used a big tin can,I think it held some Clam Chowder originally.
Just take a tape-measure to the store,and find a can that's close to optimal.
I got a nice 10dB gain on mine. smile.gif


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Private_Walter
Posted: August 24, 2008 12:55 am
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This was in a popular science magazine a while ago, although it was for a phone.

http://www.popsci.com/diy/article/2006-10/...-and-parts-list

seems a little expensive, although I'm betting you guys could hack together one for cheaper.

EDIT: Found a video of it.

http://www.youtube.com/watch?v=zwNZGuKzGWY

Austin


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telomere
Posted: August 24, 2008 01:25 am
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In actual tests with a pringles can vs. many directional antennas, the cantenna did no better, and sometimes worse. There's nothing special about it, except that it is inexpensive to make.

As long as you're paying attention to the details, any directionality is a huge bonus over the "omnidirectional" (really not omni, but somewhat close) antennas.

If you buy a parabolic dish, you can get results that make a pringles can look like a toy. biggrin.gif


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Fallingwater
Posted: August 24, 2008 02:39 am
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A parabolic dish being the same thing as a satellite dish, right?

Sorry, I'm not very practical with radio stuff terminology tongue.gif


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telomere
Posted: August 24, 2008 04:51 am
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parabolic - parabola. Satellite dishes are often parabolic.


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AwesomeMatt
Posted: August 24, 2008 08:53 am
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http://www.leechvideo.com/video/view3489580.html <-- Have a printer? Aluminum foil? Gluestick? You're done. "Don't even bother asking mom, she won't care."

When the wifi standard was dreamed up and the FCC approved it, they anticipated people doing stuff with it like hooking it up to cans and dishes and stuff. In the US, it's perfectly legal (not legal to steal someone's net access, but, legal to transmit and use the antenna).

http://www.engadget.com/2005/11/15/how-to-...d-dish-antenna/ <-- Read.

http://www.engadget.com/2005/07/31/unampli...t-at-125-miles/ <-- These guys set the record between two mountaintops, but their own site documenting it is gone now sad.gif

http://www.engadget.com/2007/06/19/venezue...cord-237-miles/ <-- How about 237 miles? That's like, sitting in San Fransisco and stealing some dude's wifi in LA. Though, South America has some of the most massive altitude changes in the world. Curvature of the earth is your problem at that point, as you need LOS.

TV satellite dishes are parabolas, but they are not the exact back of the parabola, they're a slightly lower segment. When you point them, you're actually way off from where you think they're pointing, by like, 30 degrees low. If you want a dish to go horizontally, the pickup should be pointed down about 30 degrees into the dirt. This is so the pickup doesn't block the sat signal from actual satellites.

Using actual antennas and wiring is a bit tricky, and very sensitive. I recommend not doing that. Just get a USB wifi dongle, toss it about where the sat pickup was, and hook up a USB extension cord to bring it to a computer. USB is good for up to about 20 feet, with some more expensive USB-extension options after that (it's timing-limited, not strength-limited).
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tekwiz
Posted: August 24, 2008 07:59 pm
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QUOTE (Changes @ August 23, 2008 03:20 pm)
Just how directional would a satellite dish antenna be? Are we talking "gets just the one AP it's pointed at with a margin of 10 centimetres" or "a building two hundred metres away"?

Also: am I right in thinking the focus of a satellite dish is usually where the receiver doodad sits on its stalk? If that's the case all I have to do is put a usb wifi dongle on the stalk in place of the receiver, right?

Not quite that bad, at 200 meters, the beam from a sat dish will likely be 10 meters in diameter or so. Think flashlight beam. You are correct as to the receiver position. cool.gif


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For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

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SiliconBurner
Posted: August 24, 2008 11:16 pm
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QUOTE (Changes @ August 23, 2008 01:27 pm)
This xkcd comic, and its forum thread, have piqued my curiosity.

I knew about cantennas, but I never bothered making one. Now I'd like to try, but I have one question.
It's quite hard to believe that a pringles can is the most efficient way to make an antenna. What do you guys think is the best directional wifi antenna that can be made with generally available parts? Perhaps a satellite dish with a USB receiver stuck in the center would work better? (just guessing here.)

If you want a more versatile antenna, you could also try an omni-directional vertical collinear.
See http://www.nodomainname.co.uk/Omnicolinear/2-4collinear.htm
Up to 10 dB gain, but in all directions, so it wouldn't matter where the Tx or Rx are relative to another.
Admittedly less easy to build than a pringle-can or a metal plate as reflector, but for a stable WiFi signal, at some distance from the WAN station, this would be a good way to go I think.


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mikluha
Posted: December 23, 2008 06:32 am
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I had similar problem couple years ago when we just moved in the middle of nowhere and built a barn about 200 ft away from our house + house wall + temporary tarp barn wall. I needed Internet there. Quick. I had usb wi-fi dongle to connect to the house wi-fi. Connection was marginal - on-off. I stole spaghetti bowl (or whatever it's called) from my wife (explained her later that The Science requires some sacrifices). It's a close enough to parabola shape for all practical purposes. Put dongle inside. Spent 10 min drilling holes and adjusting. And level went from zero to 3 bars on my computer.
The system worked for 3 months until I run cable.

Cost: $5 dishware + $1 pipe
Time: 10 min

pic
Dongle mounted little bit lower than axis, so the antenna has to be tilted to compensate that shift. I'm sure by messing around mounting system I could get a much better aplification but it was good enough temporary solution

pic - another view.
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MikeGyver
Posted: December 23, 2008 11:19 am
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Google "biquad antenna"

fit one of these to the arm of an 18" inch satellite tv dish
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CWB
Posted: December 23, 2008 01:15 pm
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a lot of the small satellite dishes use an "offset look angle" ...
they actually "see" at a higher angle than the dish would indicate .


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MikeGyver
Posted: December 24, 2008 07:02 am
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Most people mount the dish "upside down", with the arm on the top so the dish can be aimed horizontal.
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GPG
Posted: December 24, 2008 12:28 pm
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SKarmytech
Posted: December 24, 2008 04:06 pm
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I just built some WindSurfer antennas from freeantennas.com and placed them in my router. It realy works by reflecting the signal to a disired area you want.


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Fallingwater
Posted: March 23, 2011 02:55 pm
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Holy thread resurrection Batman!

I've revisited the idea again, and I got to thinking... would putting a double biquad instead of a normal biquad on the satellite dish give any additional benefit? That page suggests the gain is fairly high, but then he is using the antenna by itself, and I suppose the horizontal shape of the antenna could cause problems with the round shape of the dish...


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tekwiz
Posted: March 23, 2011 07:56 pm
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All antenna gain comes from reducing coverage area from the near hemispherical toroidal pattern of a zero gain isotropic antenna, allowing the same amount of power to be concentrated into a smaller area. The tighter the coverage, the higher the gain.
AFAIK, there is little to be gained by interfacing a gain antenna, like a biquad, with a dish, because a properly set up dish already has a pinpoint pattern. It's exactly analogous with focusing a candle with a parabolic reflector. Adding a gain antenna would be like using a smaller parabolic reflector in front of the candle, sending light that would normally be emitted in the direction of interest to be reflected by the rear dish first. It does focus this light a bit better, but the gains are truly miniscule.


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moopthereckoner
Posted: October 18, 2011 10:57 pm
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what decreases signal quality outdoors?

what shapes are more effective that can be used macroscopically to channel radio waves?

will a combination of designs achieve a multiplicative/additive effect? (ex. fractal antennae inside a can)
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