JonStarbuck.co.uk

[This page is a work in progress, it is not complete yet

Also, the Pringles Cantenna is a myth, see further down for why.]

I have been reading about Cantennas and the like, home made directional hi-gain wireless antennas. I fancy making one but I don’t like the internal wi-fi card approach; the losses and complications from using long coaxial cable at these frequencies seems unnecessary to me. I searched about on eBay for a while and found a nice Netgear USB wireless adapter.

Netgear USB adapter in its case.

Netgear USB adapter with its case removed.

Closeup of Netgear USB adapter’s dipole antenna.

With the old antenna removed.

A short length of coax soldered into place (very tricky).

I am going to use it to with various configurations of antennas, dishes, cantennas, yagis, waveguides and so on to see what results i get. Initially i have it attached to an old laptop’s antenna (see picture above) and it is sat in my window to check I have not damaged the card or messed up the soldering (indeed I am using it now to upload this).

My initial experiments ended in disaster, I cut off the USB Dongle’s antenna and soldered on some coax from a laptop (see the pictures) but i was getting better results through the coax than through the antenna on its end. So I dropped the coax bit and soldered the antenna on directly but it kept beaking off and repeated attempts to solder it back on ended when there was nothing left to solder to! Other people seem to have managed it, but I can’t and it is not like I am so unskilled with a soldering iron either!

Instead I have bought an older USB non-dongle-type wifi adapter from eBay, a NetGear MA101, which I have attached a very short pigtail to, so I have a long USB lead and a short pigtail, which gets over the problem of a long coax being very lossy. Basically i am copying one of these designs, more specifically this one.

So far, still not much of a result………. The whole apparatus works fine but seems to be somewhere between very slightly directional and not be directional at all. As you can see from the photos, I have tried to extend the can with card and tin-foil, and shield the card’s on-board antenna with some foil, but this made no difference.

Next I am going to upgrade is to ditch the tin can (which is almost 100mm diameter, incidentally) and make a nice smooth-sided, flat-ended and long tube.

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Software

I like the look of this http://www.netstumbler.com/downloads/

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Cantenna:

This website seems to be one of the best from my point of view, a nice simple explanation of the maths and dimensions for a 100mm can which is what I happen to have here. So the can i have is a lot less than ideal, it is not smooth or the ideal size, but it will do for my first experiment.

Great site which includes lots of good info on Cantennas and the Pringles Cantenna Myth.  If you take the time to work it out and not just read the crap others have written you will find the Pringles tube is too narrow and  would need to be impossibly long at this frequency.

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Some links and other bits and bats for later:

Cute set of no-budget experiments from New Zealand:
http://www.usbwifi.orcon.net.nz/

I have good reson to beleive the following will not work:
http://www.rahul.net/dold/clarence/usb-can/im000742-800×600.jpg

http://flakey.info/antenna/waveguide/
http://www.usbwifi.orcon.net.nz/
http://www.oreillynet.com/cs/weblog/view/wlg/448
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12612
http://flakey.info/antenna/waveguide/
http://www.unwiredadventures.com/unwire/2005/12/defcon_wifi_sho.html
http://www.engadget.com/2005/11/15/how-to-build-a-wifi-biquad-dish-antenna/
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12611