Wireless Internet Cantenna

Picture of Wireless Internet Cantenna
This is about making an antenna using a usb wifi adapter, and an old fire extinguisher I never got around to refilling

I used a hacksaw, a dremel with the heavy-duty cut-off wheel and some small files

To figure out where to cut, I drew lines to cut along, on the outside of the extinguisher body. This includes a nice ink pen, an architects scale (tri-angle type ruler), and a piece of paper. The ink pen could have been a scribe, instead. A sharpened nail, or ice-pick would work for that

I went and recycled a few photos between steps, as I didn't take enough pictures during the construction
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Step 1: It all started with Pachanka's Wokfi

Picture of It all started with Pachanka's Wokfi
After reading another instructable on how easy it could be to build a parabolic antenna, I wound up with this

And this, is a 24 inch wok I found at Goodwill for $7, mounted on top of a telescope tripod. Handles were removed and the thumb-fi taped and hung off of some string into the focal point

But before I could test this wokfi, I read yet another instructable for a yagi cantenna, and after following some of the links in the comments I decided to build this cantenna

Step 2: In hindsight

Picture of In hindsight
I knew I should've stopped and took pictures, but I didn't.

So this is what I started with, a Kidde fire extinguisher that was empty and had been cluttering up a shelf for several years now.

It has an aluminum body with a nice flat bottom, which I thought would work well as a waveguide.

It measured around 3-1/4 inches outside diameter. This is like the kind you might find in a car or around a kitchen. If it had a plastic body, I suppose it could be wrapped in aluminum foil, but I would've scrapped the idea and gone for some exhaust tubing or something like that.

Step 3: Deconstruction

Picture of Deconstruction
I already threw all the leftovers out, so no pics of that here, sorry

Seeing as this extinguisher was empty and not pressurized, I didn't need to empty it first. But if I did had to do that, I would just pull the safety and shoot the thing untill no air came out

The fun part was years ago with my nephews assistance, right now all I need to do is unscrew the top and dump out the remaining powder

The top unscrewed easy, by hand. No fatal explosion. For the faint of heart, you could tie the trigger valve open so that there's not even a chance of pressure building up while it sits, but why miss out on the adventure?

After filling with some water and rinsing out the last of the powder, I needed to figure out where to cut this thing

Step 4: Cutting the head off

Picture of Cutting the head off
I used a calculator on this website: to find my measurements

Using a close estimate of what the inside diameter might be, about 3-1/8, I decided to cut as close to the top as possible, but without any of the curve from the tops shoulder left behind. I could shorten the can later, if needed

This is where that piece of paper comes in. This is a standard technique that I use on so many other projects, that it probably should have it's own instructable. But it's the first time I'm bringing this up, so I'll include it here

I'm going to be using a hand-held hacksaw, and I want to make a nice and even cut so that the top is square and flat. A quick and easy way to do this is to first draw a line to use as a guide, going around the extinguisher

To do this, I wrap the paper around the can, and because it's a standard printer paper, it has a very straight edge on all sides. This means that after wrapping it tight, and after adjusting the paper so that the edges where it meets are lined up with each other, all I have to do is slide it up to where I want the cutting line, then carefully draw along the edge of the paper, all the way around the top of the extinguisher.

Once I have a nice cutting line to go by, I follow that with the hacksaw and proceed to cut the top off. The after the top is off, I went over it with a flat file to even it down and give the inside edge a nice crisp corner. I think that any imperfections here might disturb the radio wave

Step 5: Lengthy Layout For A Thumb-Hole

Picture of Lengthy Layout For A Thumb-Hole
Still using that same calculator, now I have a better measurement of the inside diameter: 3.16 inches approximately.

This gives an upper and lower frequency range that looks good. The full wave length is 11.07 inches, 3/4 wave is 8.3. I decided to leave the length alone

The 1/4 wave measure of 2.77 inches, is where I want to position the thumb-fi, and I reasoned that this is probably the center of the thumb-fi

First, another standard layout trick. Using any nice length of angle stock will allow a method to draw lines perfectly along the length of tube or pipe. In this case, I'm using that funny ruler. Laying it along the length of the extinguisher, near the rear end, it fit's automatically and I use that to draw a starting line. Doesn't matter too much where as long as it goes through the likely placement of the hole, but it will help if the line ends right at the bottom of the extinguisher, because I'm going to eyeball the next lines position based on the first one

To find where to put the second line, I rested the thumb-fi on the bottom of the extinguisher so that it lined up with the line I had drawn. Then I placed the ruler so it lined up on the other side of the thumb-fi. Carefully holding the ruler so it wouldn't budge, I just let the thumb-fi fall onto the work bench and proceeded to draw the second line along the length of the extinguisher

These two lines give two sides of the hole that will be cut. The quarter wave dimension will now be used to find the other two sides. I fudged this step, I made a reasonable guess where the bottom of the inside of the extinguisher would be. So, with the ruler laid along the length of the extinguisher, I slid it down to the bottom and lined up the zero with where I thought the inside bottom might be, then made a mark at 2.77 inches up. This is going to be between the last two sides I will be marking out, now I need to know how thick the thumb-fi is

Another bit of eye-balling here, as I just placed the thumb-fi on the ruler and slid it down untill one edge looked lined up with zero, then looked down the other edge to find it's approximate width. Slightly over 1/2 inch

Now, placing the ruler back on the extinguisher, and putting one edge of the ruler on that 2.77 inch mark, I slid the ruler along that mark untill the number one mark on the ruler lined up with the 2.77 mark on the extinguisher. Now I just go a 1/4 inch to either side and there's my last two sides, almost. One last time with that paper wrapped around the extinguisher, lined up with each of those last two marks. Now the last of the sides are drawn. I expect to have to use some filing to finish the hole, and I was right as we'll see next....

Step 6: Cutting the Thumb-Hole

Picture of Cutting the Thumb-Hole
I have a single-speed Dremel plugged into a vari-ac power supply. So it's actually a variable speed Dremel. Using a cutoff arbor and using the 1 inch heavy cutoff wheels, I cut along the thumb-hole lines I drew. It's not necessary to cut all the way to the corners on the shorter sides. I just went as close as I could, and the cutout was able to break loose just by pushing it around by hand. I would've used a utility knife to finish the cuts if I had to, but it wasn't needed this time

After a bit of filing to clean up the hole, I found that the thumb-fi didn't want to go all the way in. So, some more filing on each side to keep it centered to the starting dimesion. I was only off about a 1/16th

Step 7: It's a Cantenna!

Picture of It's a Cantenna!
As you can see, the thumb-fi went right into the side. I used some duct tape to hold it in place

Then I went back to the shooting range to see how this compared to the wok-fi

I used the telescope tripod, and tied the can to it so that it could be rotated as well as aimed up and down or side to side

It didn't work! I was able to see a bunch of networks, but couldn't get any of them to lock in. Bummer...

Step 8: Fine tuning

Picture of Fine tuning
After borrowing some beer and a sandwich from my shooting range friend, I decided to adjust the depth that the thumb-fi was placed inside of the can

That did it! Now I can get some signal levels!

The thumb-fi is about a half inch into the can.

Step 9: Final Conclusion

Picture of Final Conclusion
It works. And now I want to know how this will work mounted in front of a retired dish-tv reflector

Using the Cantenna, I was able to get about 12 signals in just one direction. Though not as strong as I would like, still a bit better than the Wok-Fi did

The best signal looked like it was a mile away, going by where the Cantenna was pointed when I moved it untill the signal dropped off.

Edit: 3-26-'09 Well, seeing as I continue to get comments on this instructable I guess I could say a bit more.

The retired dish-tv experiment was an improvement on this. See The Wireless Internet Cantenna gets Dished

But my best performance is a simpler approach. Just add a cone to the end of this fire-extinguisher to get the Conetenna. I'm regularly establishing a connection about 5600 feet away from my location using the Conetenna. The connection is too slow for any kind of streaming video, but enough to check my e-mail.

At another location, using the Conetenna, I've established a 100% 8-out-of-8 signal with the maximum data rate possible over the adapter - from across the backyard and inside of a garage.

I was going to build an even better antenna, but the Conetenna is enough for now, and other projects beckon. Thanks.
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spawnos37172 years ago
Would it be possible to multiplex a couple more wifi adapters into "the can" to further acquire signals?
Shadetree Engineer (author)  spawnos37172 years ago
As far as I personally know, I very much doubt it. Doesn't mean it's impossible, but I think there'll be all kinds of technical issues that will make such a build way too complicated. Just inserting a dead unit will interfere with the first one. Multiplexing just two USB adapters in any kind of antenna configuration is too much challenge for me! Even if all you did was use the adapters as-is with no can. I think you'll need to write a custom driver to do it.

If all you want to do is just grab more signal, the best approach is to increase the physical size of your antennas 'ear'. In other words, take a look at parabolic dish antennas. The bigger the dish, the more signal you can grab out of the air. And any size dish can be made to work with the same adapter.

A less effective, yet improved alternative is to add a cone to the end of the can.

PS: Something you might want to take a look at is what I'm using these days. A Ubiquiti Bullet.
sn00ze3 years ago
this page has some good images explaining where everything goes
sn00ze sn00ze3 years ago
Shadetree Engineer (author)  sn00ze3 years ago
Nice. That site keeps all the research for can dimensions as simple as possible.
cotton6 years ago
it will work on a old satilite dish
Shadetree Engineer (author)  cotton6 years ago
Yes, it will.
no i meant as in use the oringinal antana at the end of the arm poiting at the dish and wire it into a wireles card
Shadetree Engineer (author)  cotton6 years ago
Oh okay. Main problem is the waveguide that came with the dish is about one inch in diameter, which is for a much higher frequency than 2.94 Ghz. I would recommend installing a coax connector into a can like my fire extinguisher approach, with a tuned length of wire soldered on the inner end to act as the active part of the antenna. Then you can connect a pig-tail from a wireless card to this antenna. Try Seattle Wireless this site seems to have some current info, they link to cantennas, which use this connection method.
enf0rcer1213 years ago
i just completed mine like this and picked up 7 more connections
bugmenot54 years ago
 Had there been any pressure inside the extinguisher there is no possible way you could have opened it by hand. For experimental purposes, try doing so with scuba diving equipment.
Shadetree Engineer (author)  bugmenot54 years ago
Uh Ok.  That must be why I emptied the extinguisher!  Though I dimly recall having thoughts of an exploding white cloud of powder shooting into my eyes as being somewhat instructive.

Your proposed experiment I'm assuming, is to attempt unscrewing a fully pressurized scuba tank?  Huh, I remember wanting to do that when I was in high school.  I don't know if it was the A-Team or McGuyver, both of those shows were playing at the time. But they were the inspiration for that scuba tank fascination.

Did you know that a steel scuba tank if cut in half, has a wall thickness of over 3/8ths inch?  It took me a while with my sawzall, but I've done that once.

11richie214 years ago
do you know if this "cantenna" works with an xbox 360 and can you use a wifi max adapter. thanks
Shadetree Engineer (author)  11richie214 years ago
I'm not too sure about the 360 adapter as I never used one. If it can be connected to the 360 by a cable, maybe 6 feet in length, then it should be no problem as you would just put the 360 adapter inside of the can instead of the adapter I used.  If you are using the official 360 adapter, that appears to use an external antenna, so I would just put the antenna inside the can with the adapter arttached to the outside. Use a usb extension.

The WiFi Max adapter appears to be an access point for your 360 to connect to. It looks like it should work exactly the same way as what I did, just accomplishing a different purpose.

Did you know that you can use a router with built-in wireless on your 360 to connect to another router? Look at DD-WRT, that's an alternative software that can run on a router. It allows turning the router into an adapter, which means you can plug an adapter into the ethernet port instead of the usb.
ok thanks! good to know
sn00ze4 years ago
(removed by author or community request)
Shadetree Engineer (author)  sn00ze4 years ago
Nice site, keeps the panic level down!
McGragger5 years ago
is this the correct way to face the thumbfi ? Which side is the internal antenna on?
Shadetree Engineer (author)  McGragger5 years ago
I'm not sure what you mean by 'facing the thumbfi', but in this photo I made the mistake of inserting the adapter too far inside of the can. I didn't find this out until later, when I adjusted the insertion depth for best signal. I have tried putting the adapter into the can with either side facing forwards, and found no significant change in signal levels. I never cracked this model of adapter, so I'm only assuming that the internal antenna is located at the tip, that it is likely formed directly on the circuit board, and that there are no other components inside of the adapter to block the 'backside' of the internal antenna. ps - check out the 'Conetenna' tutorial, where I add a cone to this can to gain more signal. I think I put in some advice on cone layouts that can be sized for any dimension of can opening. My latest connection with the 'Conetenna' is just over a mile, netting a very useable connection speed.
i would say so!
k_man935 years ago
looks like a cool hideout room thing... and its practical!
geeklord5 years ago
Gotta love those people who leave their wireless' name as the default and don't add any security :D
i love that too
xvitox5 years ago
Hey do you wanna send me a link for the wireless adapter that you used?
Shadetree Engineer (author)  xvitox5 years ago
It would be nice if the transceiver was at the lower side under the can so a boot could be made of silicone to keep water (rain) off the USB connector.
The signal is polarized, it works better if you rotate the antenna for best results, not for water-proofing. If you make a boot, then it shouldn't matter which way it is.
lil jon1685 years ago
how do i get wirless inter bet when i have DSL
Shadetree Engineer (author)  lil jon1685 years ago
DSL is usually a really fast connection to the internet. Faster than most homemade wireless set-ups. I'm going to assume you have a DSL modem and don't mean to abandon the DSL connection, but would like to add wireless to it. Or does the modem have wireless already, and you just need to install wireless on another computer? In either case, buy a router with Wi-Fi built-in, or a Wi-Fi adapter. And in the case of the adapter, follow this instructable or one from the Wi-Fi Group to connect to your modem from the treehouse!
can u send me a link to a wifi adapter cause i dont relly know wat ur talkin about
Shadetree Engineer (author)  lil jon1685 years ago
Ah well, sure. Check your message box.
For some reason, i just don't think a cantenna is as good as a wokfi or parabolic reflector.
Well, in the case of my waveguide 'Cantenna' described here, you are absolutely right! If you should happen to see a newer antenna creation, called the 'Conetenna', you will note that it uses this can - simply adding a cone to the end to increase the signal. A really good parabolic will still beat the Conetenna.
I'll work on it, internet is expensive.
danfolkes5 years ago
Hey, cool instructable. I like the use of USB adapter insead of having to deal with pigtails and wire. You might consider popping off the case to the thumbdrive to see if you can position the inner antenna a little better. It might be out of wack. I am going to make one of these out of a juice can!
Shadetree Engineer (author)  danfolkes5 years ago
Well, I've heard a rumor that the adapters built-in antenna could be oriented 90 degrees wrong for a side mount into the can. It was recommended to put the adapter into the end of the can to compensate. The built-in antenna is usually going to be formed from the copper plating that is a part of the circuit-board. You would be better off converting to a pigtail if you want to perform surgery on any adapter. Not a crazy idea if you consider that there are self-powered usb extension cables to allow some really flexible installations!
deejaydee5 years ago
im going to buy a wireless adapter to connect to my friends wireless thats about a block away .. and i was thinkin of buying something cheap like the "ENCORE ENUWI-G2 IEEE 802.11b/g USB 2.0 802.11G Wireless Adapter" .. and im wondering will that work?
Shadetree Engineer (author)  deejaydee5 years ago
Yeah should be just the same, only the size of the hole you cut will be a bit different. I've run into a good point of view that brings up an issue with how the antenna inside of the adapter is oriented. That is, for some USB adapters, you will get a better signal if you install the adapter on the end of the waveguide tube, instead of on the side like I did here. Check out what happens if you put a tuned cone on the end of the waveguide, like my conetenna instructable.
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