Wireless Internet Cantenna

Step 2 In hindsight

I knew I should've stopped and took pictures, but I didn't.

So this is what I started with, a Kidde fire extinguisher that was empty and had been cluttering up a shelf for several years now.

It has an aluminum body with a nice flat bottom, which I thought would work well as a waveguide.

It measured around 3-1/4 inches outside diameter. This is like the kind you might find in a car or around a kitchen. If it had a plastic body, I suppose it could be wrapped in aluminum foil, but I would've scrapped the idea and gone for some exhaust tubing or something like that.

Comments

[sonnytiger]

can it work if you use another size fireextinguisher ore any other type of metal tubing ect? Mail me at [e-mail]

[Shadetree Engineer]

From what I've seen, the precise inner diameter you use can vary a lot and still work. But, to get the best performance out of 2.4 Ghz, you need to stay within a range of diameters. I can't find my notes at the moment or I'd put some numbers down here, this particular extinguisher was near the small end of the range, so go bigger in diameter. Keep in mind that whatever inner diameter you use, will change the best length to cut the tube, and also for where to cut the hole for the thumb-fi.

You can use any tube, but the extinguisher has the advantage of the end already being capped, and for this extinguisher, capped flat and with an almost perfectly square seam.

If you want to use any other type of can, such as a soup can, you will have as good a result as I did with the same care taken to make all the dimensions come out close. I recommend spending an entire day to read this:

http://wireless.ictp.it/school_2003/docs/radio/microwaveantennabook/contents.htm

I just remembered this site today, it was bookmarked for a project I was researching two years ago. At that time I was trying to make an antenna that would take all of the energy from a magnetron out of a junked microwave oven, and beam it in one direction like a ray-gun. It took me a few weeks, but it finally dawns on me that I've been seeing several times now that the thumb-fi and the micro-wave ovens are on the same frequency! I had this 2.4 Ghz feed-horn sitting right there on a shelf over the work bench where I made this cantenna! Bigtime slap to the head here....

By the way, I highly recommend going to the site I mentioned and building a feed-horn with metal-lens setup. That might be my next project as it is.

[sonnytiger]

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