How to build “cantenna”, a wave guide antenna out of a coffee can November 27, 2007Posted by GuySoft in cantenna, Crictor, diy, Hamakor, linux, open source, wifi, wireless.
Tags: cantenna, computers, diy, hacking, howto, linux
This is really a translation of a post I wrote in Hebrew out of Linmagazine.
Here is my own DIY guide to build a waveguide antenna. This antenna will dramatically boost your wireless connection to a specific direction, enabling connectivity to great distances.
- A coffee can with a diameter between 70mm- 110mm
- A copper wire, as straight as possible
- A female N-type connector
- A Pigtail – a cable that connects the cantenna to the wireless card (the card needs an external antenna connector.
- A wireless card with an external antenna connector.
stages of building the cantenna
Stage 1: Getting the parts
Of course, the first part is finding the can in the right size. As I wrote, the diameter should be in the magical range of 70mm to 100mm. This number is govern by the oscillation of the radio wave inside that can (The wave in wireless 2.4 GHz). The depth of my can was 117mm, it was a little more than the minimum given. Basically, you need the can to be as deep as possible. Use this online calculator, to calculate the minimal depth, before having serious signal loss.
I found my can at the supermarket. It was supose to be used for storing coffie. there were good reports using wiskey cans. Just to make one thing clear – Pringles cans are too small fore the wavelength and they don’t last well anyway.
The copper I got in a normal electronics store (in this case “Kashayof” in Jerusalem). The calculator i mentond above, will give you the length and position of copper inside the can. My result is 43mm for distance from the base, and 31mm for length. Just make sure you get this right :) .
I also got there the N-type female connector, here is a picture so you can see it:
The wireless card i use is called Engenius EL-2511CD+ EXT2 (picture at the bottom), its pretty old, I am sure you can get now something better. It cost me about 45$, including shimpent, which isn’t much. It has an output of 200mW, Which meens its sensative to long ranges. Really, any card will be alright, but the higher the sensitivity and trasmission, the better.
I also had to get the pigtail cable from eBay, because my card uses a connection called mmcx. A getting this stuff in Israel is impossible. So I orderd it from Hong-Kong, and it cost me about 20$.
There are various qualities for cables, so you better pay attention (I had a low quality cable, its a LMA-100).
Part 2: Assembly
In this part, I’ll mostly use pictures, so you can see all the step (its more effective).
The first thing I did was to take off the paint off the surface we are going to dill on. This wasn’t written anywhere on the net, however I thought I should do it just for safety:
After that, I marked the place where the hole was drilled:
For the next stage, my father will join us. Since he owns the Drill in our house – go dad!!!
Here is all the equipment ready, in the safist place on earth to drill – the kitchen (still, I don’t recommend doing this part at home, use a garden or something).
BTW, if you ever want to see how shakesphare look in Hebrew – the page under the drill is “A midsummer Night’s Dream”.
Of course, don’t forget to secure the can before you drill, this needs to be very precise:
Here I am drilling:
Making sure we are on the right track:
We have a match of sizes! :
The holes for the screws were added by someone else. I sould have done it myself, but I had no small drilling heads. If you have them, it should be easy:
Stage 3: Soldering the copper wire to the N-type connector
This is the part I liked best, Soldering the copper wire to the connector. You need to get the wire as straight as you can. For some strange reason, there is no straight wire here for sale. So I did that myself.
Here is a picture of the soldering process:
Try not to make pointy edges with the solder, microwaves like smooth surfaces.
Here is a picture of my tidy working place:
In the end, you better screw the connector to the can, should take a second of two. Here is a picture of the inside of the can, once all is assembled:
And here is a picture of the final product:
And here is a closeup on the connector:
stage 4: configuring the card on Linux
The card uses the module hostap_cs. this module works well, and as of kernel 2.6.x is inside the kernel source.But for some reason, it didn’t work right away. It drove me nuts, took me about to days to surf in windows (oh! the shame), but in the end, I figured it out, well 2 problems. The first was that the irq adress was taken, so I fixed that adding the following line in /etc/pcmcia/config.opts :
exclude irq 5 exclude irq 7 exclude irq 3 exclude irq 4 exclude irq 11 exclude irq 10
The harder part was because the card wasn’t working still. Ironically, I found that was because the driver was crashing with the other wifi card I had on the laptop. So i removed that module:
And thats about it, I found a linksys network not too far from me, about 1km away. And I can surf the net all thanks to a coffee can.