Table of Contents
Cantenna, directional antenna with gain
Doc Revision: V1.0
Date: 28 Jan 2007
By: RF Peep
Many people have been asking how to boost their wifi signal, here is my small contribution with an antenna I made and use successfully.
The objective of this tutorial is explaining how to build & use a simple antenna system with USB adapter.
This antenna is directional and very simple in construction and costs only 80p or 1 Euro or $1.40 !! for the can, excluding the cost of the USB stick (which I presume you already have) and blue tack. Basically Blu-tack is a kind of plastersene. My USB stick is a D-Link G122 ver B1.
It’s a can which contained dog food, any can of the same size will work. This one measure:
Length = 170mm, Width = 100mm, Length from inside bottom of can to centre of USB stick = 40mm
Cut a rectangular hole as shown in the photo Pic 1. Then smooth the entrance of the can so the edges are not sharp, I used the rounded end of a hammer.
Put the USB stick inside the can and secure it with blu tack or silicon sealant. You will need to adjust the USB stick by moving it in and out for optimum received signal by pointing the can at your AP and using airodump-ng and watching the signal strength numbers go up, signal quality will go up too (airodump-ng V0.7 has quality read out). You could also use Netstumbler on windows to make your adjustment. Once you have the optimum position then secure it using blu tack or silicon sealant.
The AP needs to be a reasonable distance away (not in the same room) so that you don’t swamp the receiver and get a false reading on your software. The open end of the can is where the wave enters, point his towards the AP! It is highly directional and a few degrees left or right of the target will make a significant difference.
The measured gain is around 13dB which is 20 times the strength of the USB stick without the can. This is amazing gain for the simplicity and “cheapness” of the system! This is what I measured using professional measuring equipment from work, I’m astonished at the results myself! Due to the internal construction of other USB wifi devices the gain may vary. Also by inserting the USB device the other way around could improve signal strength, it is all very device dependent. I then use a short length of USB cable to connect the PC to the Cantenna.
The size of the can is important when designing a proper antenna system, however, the parameters of this can are in fact not the correct ones for the frequency of wifi but as you will see, work very well and are a compromise.
Once constructed, the can should be placed on a tri pod or some form of support facing the AP. I used 3mm copper wire, which is easy to work with, to make a simple stand for the Cantenna.
Please feel free to ask questions or leave feedback on the forum about your construction and use.