Create a cantenna to drastically extend your Wi-Fi signal! Works great with a router that has external antennas, like the old-school classic WRT54G.
Requirements For This Walkthrough
Materials
- 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)
- Solder
- Wire cutters
- Screwdriver
- 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
Downloads
- None
Knowledge, Skills, and Abilities
- Ability to solder
- Ability to install components with screws
- Basic understanding of wireless networking concepts (radios, wavelengths, frequencies, etc.)
Resources
- http://www.turnpoint.net/wireless/cantennahowto.html
- http://www.extremetech.com/article2/0,2845,1641185,00.asp
- http://martybugs.net/wireless/biquad/
- http://www.engadget.com/2005/11/15/how-to-build-a-wifi-biquad-dish-antenna/2
- http://www.radio-electronics.com/info/antennas/waveguide/waveguide-basics-tutorial.php
- http://antenna-diy.blogspot.com/
- http://www.seattlewireless.net/SardineCanAntenna
- http://wifirepeaters.net/best-wireless-antenna-for-strong-signals/
- http://hackaday.com/2009/07/07/various-cantenna-builds/
- http://www.pelaginox.com/pc/pc-cancalc.html
- http://www.seattlewireless.net/AntennaHowTo
- http://www.thanscorner.info/how-to-build-a-cantenna/
- http://revolutionof1.wordpress.com/how-to-build-a-cantenna/
How the Cantenna Works
Waveguide
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 aluminium can. If you make really large waves in the water but have a tiny 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 maths.
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.
