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Jon’s Cantenna - hi-gain, directional wi-fi antenna

[this is a work in progress, it is not complete yet, please leave comments at the bottom, thanks.]

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 come 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 braking off and repeated attempts to solder it back on ended when there was nothing left to solder to! Other people seem to have manged 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 somwhere 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:

This is exactly what I am thinking of off - http://www.usbwifi.orcon.net.nz/
http://www.rahul.net/dold/clarence/usb-can/im000742-800×600.jpg
http://www.qsl.net/n9zia/wireless/pics/tincanant.jpg
http://flakey.info/antenna/waveguide/
http://www.usbwifi.orcon.net.nz/
802.11b Homebrew WiFi Antenna Shootout
http://www.oreillynet.com/cs/weblog/view/wlg/448
Antenna on the Cheap (er, Chip)
“Cantenna” - yagi design for 802.11b wireless application
Pringles Cantenna - will not work!
DX Zone list of WiFi antennas - all sorts of designs
Pantenna
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
Common Wireless Antenna Connectors
Waveguide on Wikipedia
Feedhorn on Wikipedia

Written on 20 February 2008 by Jon under How to make a with 1 Comment

Collecting waste oil (legaly)

I have been offered waste oil for free from a local pub but they need from me a Duty Of Care note in order for them to be happy to let me take it away.

I want to start producing my own WVO using my WVO Processor.

I have contacted the Environment Agency by both email and telephone in order to find out how to do this, but so far have had no response (PS - note second comment below). I know there are exemptions to the requirement for a waste carriers and waste disposal licenses for small bio-fuels producers, homebrew garden-shed-biodiesel makers, but the EA don’t seem able to tell me about them.

PS - Download Waste Transfer Note mentioned in second comment below.

Written on 16 August 2007 by Jon under Biofuels, How to make a with 2 Comments

Jon’s Burninator / propane puffer

I said I was going to have a go at making one of these here and I have a working prototype now. Its ignition system is not yet working, I want it to be automatic and electrical, but we tried it out last night with a small methylated-spirit burner instead and it worked well!

We only ran it up to about 2 bar but it did exactly what I wanted it to, it blew large brief balls of yellow flame into the night sky when i hit the go button - what is more it did not blow up or kill anyone, which was a relief.

How it works:

The propane gas builds up pressure in in the second pressure chamber (limited to 2 bar for now by the regulator) and is released by the solenoid (bought from eBay for next to nothing but quite expensive normally) in short bursts.

At the same time as the electrical pulse opens the solenoid, the car ignition coil is (supposed to be) fired, igniting the gas as it escapes - but as of yet I have not built the necessary driver for it (i tried to make one using just a relay, but it did not work).

[ later note - while the square wave driver bought worked well for making the ignition coil make decent sparks they were not strong enough to ignite the gas as it escaper, so it is back to using a pilot light. ]

A friend suggested i look up Ruben’s Tubes……. and they do indeed look fun!