Create a cantenna to drastically extend your Wi-Fi signal! Works great with a router that has external atennas, like the old-school classic WRT54G.
Requirements For This Walkthrough
- A wireless router with external, removable antennas, preferably with custom firmware or a wireless USB dongle with a removable antennta
- Mac or PC
- Empty 1qt baby formula can or other similarly-sized aluminum can
- Female N-connector, chassis-mount
- RP-TNC-to-N-male cable for connecting to most routers (a.k.a. pigtail) or an N-male to RP-SMA-male cable for connecting to USB adapters
- Screws (sometimes they come with the chassis-mount N connector)
- 12-gauge copper (if you have scrap cables, you could also unsheath them and see if the copper wire is thick enough to fit into the N connector)
- Soldering iron (a fine-tip with lower heat works best)
- Digital (preferred) or analog calipers; or just a tape measure
- Can opener (or something to remove the lid with)
- Fine-tip Sharpie or other utensil to mark the location of the screws
Knowledge, Skills, and Abilities
- Ability to solder
- Ability to install components with screws
- Basic understanding of wireless networking concepts (radios, wavelengths, frequencies, etc.)
How the Cantenna Works
The aluminum can acts as a medium for the radio waves to be guided through, hence the term waveguide cantenna. Radio waves will be “guided” into the can and interact with the wire element, which sends a signal down the pigtail cable and then to your computer or router.
Dimensions of the Can Matter
Each radio frequency has a different wavelength. The wavelength of a signal is the velocity of the wave divided by the frequency. If you can, imagine you can create waves in a small pool. The velocity is the rate at which the wave changes position. The frequency is how many waves you can make in x amount of time. The wavelength will be the distance between each wave you produce.
Now imagine you want to catch some of those waves in an aluminum can. If you make really large waves in the water but have a really small can, you won’t catch many or they will just break up. If you can perfectly match the size of your waves to fit inside the can, you will get capture the most water, or in our case, a wireless signal. The only difference is that radio waves are invisible. In order to find out the right size of the can, we need to do some math.
Guidelines to Cantenna Dimensions
There are a few basic guidelines to follow when making a cantenna. This will also help conceptualize what to do when making it or if you are modifying the can for a different frequency.
- The length of the can should be longer than 3/4 of the wavelength
- The diameter of the can should be longer than 1/2 of the wavelength
- The copper element should be approximately 1/4 of the wavelength
- The copper element should be x millimeters away from the back of the can (rear standoff)–this is based off the overall diameter of the can. Use this calculator to determine this
There is an online calculator, which will help you determine the dimensions of your cantenna.
Formula for Calculating the Wavelength
First, it is important to know that radio waves travel at the speed of light, which is about 300 Mega meters (Mm) per second (the exact speed is 299,792,458 meters/sec). For the purposes of an easy-to-remember formula, I rounded up and converted meters to Mega meters.
Wavelength (mm) ≈ Velocity of wave (Mm/sec) / Frequency (GHz)
w = v / f
We know v will be 300 (rounded up based on the speed of light mentioned above). For f, we need to plug in the Wi-Fi frequency. You could just use 2.4, but in order to be a little more accurate, we will use two more decimal places. For channel 6 in the 2.4GHz spectrum, we need to plug in 2.437. Solving for w then yields ~123mm.
w = 300 Mm / 2.437 GHz
w = 123.102175
Now that we know the wavelength for our radio frequency, we can begin calculating the dimensions of the can based on the guidelines mentioned previously.
Breaking Down 2.4GHz into Smaller Pieces
If you are confused about using 2.437 instead of just 2.4, take a look at the chart below to see how each channel has its own frequency. Or if you are feeling very bold, examine the Radio Frequency Allocation chart, which gives a very broad but complex overview of all the available radio frequencies. Basically, just know that the 2.4GHz spectrum isn’t just 2.4GHz, it is actually 2.401 to 2.483. While this may not seem like much, if you have ever changed your wireless routers channel to get a better signal, you know that it does make a difference.
Finding the Wavelength of Any Frequency
Making cantennas to work with any wireless signal
2.4GHz is a common frequency for Wi-Fi and its wavelength makes the canntenna an ideal size–not too big, but not too small. Once you start working with other frequencies, the cantenna might become ridiculously large or impossibly small. But simply using the formula above, you could theoretically make a waveguide antenna for any frequency.
Creating the Cantenna (Step-by-step)
Dimensions for the Can
The size of the can will make a difference on the quality of the signal. I will be using numbers from the How the Cantenna Works section above to calculate the dimensions.
If you were able to find the same can that I used (a 1qt Enfamil baby formula can), then you can simply follow the instructions below. If you have a different sized can, you will need to calculate the dimensions based on instructions above in the How the Cantenna Works section. You should still be able to follow along, but any specific dimension steps will need to be modified to suit your can.
Clean the Can
- Empty the can by using its contents as intended (give baby formula to a baby; drink juice; or consume food that the can contains, etc.)
- Clean the can
- Remove one of the can’s lid
- Remove the can’s label
Prepare the Can for the N-connector
- Measure ~63.5cm or ~2.5in from the back of the can (this will be different if you are not using the same can that I did)
- Mark this location with a Sharpie marker Note: This will be the location of the copper wire element
- Drill or cut a hole into the can making sure that the center of the circle lines up with the measurement above.
- Drill four screw holes into the can using the N-connector as a guide for their location
Cut the Copper Element to Size
- Cut a piece of 12-gauge copper element to a slightly longer than 31mm (this will be different if you are not using the same can that I did)
Note: This part is tricky because it needs be 31 mm from the point it exits out of the N-connector. In order to solder it into the connector, it needs to be a bit longer. I suggest cutting a larger piece, fitting it into the connector, and then trimming it down after it is installed.
Solder the Copper Element into the N-connector
Once you have the copper element cut to size, it needs to be soldered into the connector. If you have never soldered before, learn how, and then cut a few pieces to practice with before working on the actual connector.
- Solder the copper element into the N-connector
Caution: Be careful not to melt the plastic contained in the N-connector. It melts easy, so I would suggest using a soldering iron that has lower heat and a fine-tip.
Attach the N-connector to the Can
Once the N-connector is complete, you are ready to mount it to the can using the four screws.
- Screw the N-connector to the can
Connect the Cantenna to a Wireless Router or Wireless USB Dongle
Your cantenna is almost done; just connect the pigtail cable from the cantenna into a wireless router or wireless USB dongle. The router or dongle needs to have a removable antenna. The picture below shows the classic WRT54G being used. The great thing about this router is that you can add DD-WRT firmware, which will give you the ability to choose which antenna is transmit and which is receive. It will also allow you to adjust the power so you can increase the range even more.
- Screw one end of the pigtail into the cantenna’s N-connector
- Screw the other end into a compatible router or USB dongle