How to Make a Cantenna - Homemade Wi-Fi Antenna
In this age, nearly every house that has a broadband Internet connection probably has wifi as well. Wifi has made the tedious and sometimes difficult task of home networking a largely automated one. In the past, someone had to stretch long and unsightly LAN cables around their home or office to setup a network. The only other option was to have a professional crew come in and install the cables inside the walls, which is time consuming and expensive. Wifi, on the other hand, is as simple as plugging a wifi router into a wall electrical outlet and attaching a broadband modem. The rest of the setup is through software on each computer. No cables to mess with, and portable computers such as laptops can be easily moved from one location to another within the home or office without breaking the network connection.
However, wireless networking has some drawbacks. One such drawback is the subject of this article. Wifi routers tend to have a very good range when operating in line of sight with the computer. However, 95% of all home networks operate with the router in one room, and the computer(s) in another, or perhaps several other rooms. When barriers such as interior walls are placed between the router and the computer, wifi range suddenly drops to surprisingly short distances.
Commercial options, such as boosted wifi antennas, can help, but often signal strength will be only marginally improved at best.
However, a DIY option exists that, in my experience, has provided a substantial boost to signal strength and range with only a minimal investment...the tin-can antenna.
Tin Can (about 3 1/2" diameter and as long as possible)
N-Type Female Panel-Mount Connector
RP-SMA to N-Type Pigtail
A short length of wire
Solder and Soldering Iron
4 small machine screws, washers, and nuts. I used #4-40 screws for mine
What is Needed?
At right you can see the selection of parts that you'll need to build you tin can waveguide antenna. I know if you've searched around on this, you'll find sites proclaiming that you can build this for only a few bucks, but I'll tell you honestly, it cost me quite a bit more. My total investment was about $40 because I did not have any of the parts on hand. The single most expensive part for me was the pigtail, which I purchased from Datapro.com for about $25 plus shipping. You can probably get by cheaper if you built the cable yourself, but I could not source the parts locally to do that.
The first thing you should do when building this antenna is find the pigtail and N-type connector. These will be the hardest parts to source, and may need to be ordered online. See the Datapro link above for the pigtail I used. The N-type connector I used came from a local electronics store. This part can easily be obtained online or at any local store that deals in ham radio equipment. My local Radio Shack did NOT carry the parts I needed, which surprised me. However, stock at each Radio Shack store varies, so check there first.
The remaining parts should be very easy to find. Use any standard food can of between 3 and 3 2/3 inches diameter, and the longer the can the better. The can I used was a "Classic Meat Flavored" spaghetti sauce, purchased at a local supermarket for about a buck and a half, and measuring 3.33" dia. and 5.7" tall. The large can version of a popular brand of Sloppy Joe mix uses the same can as this. The short length of wire came from Radio Shack. Get the N-type female connector first, then look for a solid copper wire that is about the same diameter (the wire only, not the insulation) as the little brass tube on the back of the connector. I used Radio Shack brand 18-gauge solid hook-up wire. It's a little small for this, but it seems to work fine. You'll need at least an inch and a half for the antenna, but of course it's better to have extra. If you have this around the shop, that's one less item to buy for the project.
Now that you have all the parts, it's time to start building the antenna. Depending on your skill with using drills and soldering, it should not take too long to build the antenna. Mine took about 2 hours once I actually got started building it, and that included a half hour trip to Lowe's for some small nuts and bolts to mount the connector to the can.
The first step in building the antenna is marking and drilling the hole for the N-type connector to mount. Use this handy calculator to figure out where to place the hole. Input your can's diameter in the "D" field (in millimeters) and make sure the "f" field is set to 2.4 GHz. Hit calculate and the numbers you need are located at the bottom of the page, beside the "Lo/4" and "Lg/4". Lo/4 is the height of the wire probe that will be placed inside the can (not needed at this moment, but write it down as we'll need it later), and the Lg/4 tells you how far from the back of the can you need to drill the hole for the connector. For ideal operation, your can should be the same length as 3/4 of the "Lg" figure at the bottom left of this calculator, but I have not found a can available that meets this dimension. I suppose it would work if you were to attach two tin cans together, but I don't know if this would be worth the effort.
After marking the location for the hole on the can, you need to drill it out. This turned out to be the hardest part for me because my bench top drill-press did not have enough travel to chuck the 5/8" drill bit that was needed for the N-type connector to fit through. I mounted my connector on the inside of the can. If you mount on the outside, you might be able to get by with a smaller hole in the can. Don't forget to drill any mounting holes needed to mount the N-type connector while you're at it.
Once you've managed to drill the hole, it's time to solder the bit of wire to the connector. This is where that "Lo/4" number from the calculator comes in. That number is what the length of the probe on the connector needs to be. This is measured from the base of the little brass tube on the connector to the end of the wire. Try to cut your wire as close to this length as possible. Do this by sticking the wire into the tube and measuring from the base of the tube out, cutting the wire at the desired length. Once you are satisfied with the wire, solder it into the tube, minding to keep it as straight as possible. Take care not to bend this wire once you're done, as well.
Now that the connector is assembled, it's time to mount it to the can. As I said before, I mounted my connector inside the can and am getting fairly good results. Mounting the connector outside the can gave slightly degraded performance for me. I believe I am the only one mounting the connector inside the can, though. Use your own judgement and experiment. On my can, I slipped four #4-40 machine screws with lock washers into the mounting plate for the connector, then slipped the entire unit into the can. Get everything lined up and install four flat washers and #4-40 nuts on the outside. Congratulations, you've just completed a tin can waveguide antenna, or Cantenna! Now it's time to see how well it works.
Connect the pigtail to the connector and to your computer, fire it up, and see what kind of signal strength you are getting now. Remember the the waveguide antenna must be aimed at the wifi access point (AP) for best results. I have found that aiming your antenna makes a very large difference in signal strength. A couple or three degrees of rotation can change your signal strength by as much as 50%. You need to mount the cantenna to a base of some sort for maximum results. Thus far, I have not determined a proper mounting solution for my situation. Depending on your situation, a small table-top camera tripod might be ideal for mounting your cantenna. All you need is a plastic zip tie to strap the can to a base.
In my situation, I am using the cantenna in a motorhome to boost wifi reception where ever I go. At my current location, with my computer's stock omni-directional dipole style wifi antenna, I was receiving a signal strength of around 8-10% (as measured with systemDashboard Wireless Meter widget for Yahoo Widgets). With my cantenna, I am receiving an average strength of 35-40%, with it sometimes going as high as 60%. This is coming from a signal that's travelling about 200 feet, with about 5 walls and a window in the way. In my opinion, that's a pretty marked improvement over the standard antenna. I also tried a boosted omni-directional antenna from the computer store and the best reception I could get with it was about 25%, so I would say the cantenna is working very well.
UPDATE: Mounting Base
Well, I went looking for a base to set the cantenna on today. Radio Shack had exactly what I needed. It's a Targus brand Universal 6" Table Top Tripod. Purchased at Radio Shack for $7 bucks, the tripod extends to 6" tall, and collapses down to only about 4" by about an inch diameter, for travelling. The base when fully extended takes up approximately a 4.5" triangle, allowing it to be placed in many locations. Collapse the legs and it takes even less space, but it's a little unstable and the pigtail would not clear for me.
The only problem I have with it is the baseplate. It's fairly small, and tapered on the bottom for looks, I guess. Unfortunately, this doesn't leave much space to attach the cantenna down to it. As you can see in the pictures, I mounted it with four 8" zip-ties. I had to use four because the 8" ties are not long enough. Anyhow, I mounted the ties on both the front and back of the base plate, and crossed them over each other so they are pulling toward the center of the plate. Hopefully, they will hold there. If not, it should be easy to mount a small piece of wood to the baseplate and attach the cantenna to that. With the cantenna properly mounted now, my average signal strength has jumped up another 10%, to around 45-50%.
I also picked up a Targus Grypton flexible tripod to try out. It's rather cheaply constructed, but it was also only $4.99 at the local store (it's not even on RadioShack.com). It seems like it might work fairly well if you're in a situation where you need the antenna mounted to a rail or something. I got it to test mounting the antenna on the rooftop access ladder on the back of our coach, but the little tripod in the back window is working far better than I expected. I did notice the Grypton does not like weight much. My fairly small Cannon PowerShot S2 IS is too much weight for the tripod, causing the camera to tip forward or back. Keep that in mind if using this tripod for an exterior mounting, as winds may toss the cantenna with it.