Cantenna Mark 3 (USB)
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Self contained USB antenna

Firstly, why make a USB antenna?  Simple, it's easy to connect, requires no bulky cabling and best of all, there's no signal loss between the antenna and the PC.  This antenna is my final solution for a simple device that can be attached to a window and provide client access to a distant access point.

I had been operating a dog food tin with a pigtail to the radio used in this antenna for some time but the tin can was starting to get rusty and the pigtail and radio were going to get damaged sooner or later.

Some of my best results were obtained using the cardboard (foil lined) milk tub but this wasn't rain proof so the solution was to stick them all together inside a waterproofed tube!

Curiously, on the day after I made this antenna, I stumbled across this link on the Internet:-

http://www.ydi.com/usbantenna.asp

However, that costs $450 whereas my effort costs, well, about $100 for the radio and less than $10 for the rest of the parts!

Construction

My previous cantennas have used N Type connectors.  The problem here is that they require space and need to exit through the side of the plastic tube.  I wanted to keep everything safely inside so this time, opted to use a piece of LMR195 and just dispense with the N Type connector altogether.   In order to ground the antenna wire and provide physical mounting, I roughed the glaze of the foil inside the milk tub and then stuck adhesive copper tape both inside and outside the tub, ensuring that an electrical connection was made.

I then soldered the braid of the LMR195 to the copper tape - easy!

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For the feed, I didn't bother with any bits of brass, in fact my first cantenna used the original antenna wire from the Netgear MA101 USB NIC and I didn't notice any real performance gain by using a brass element, bit of welding rod or piece of copper wire.  So I just used the centre conductor, keeping the dielectric in place for insulation from the soldered braid.

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The LMR195 was then bent carefully and the tub and wire just fits inside the 4" plastic tube that was to be the housing.  I terminated this in an N Type connector for easy connection to the radio pigtail.  For the radio, I chose to use a Compaq WL110 (branded Orinoco Gold) although any USB adapter that can be modified for an external antenna connection would do.  Had I used the Netgear MA101, then i would have soldered the LMR195 directly to the Netgear PCB thus avoiding any connectors and subsequent loss.

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The above picture shows the slot cut out for the USB socket.

Below:  The internals of the Compaq WL215.  I decided to use a Wl215 instead of the Netgear MA101 because at the time of writing, there appears to be a driver issue where the MA101 driver will pause transmission for a second or so, every minute.  This isn't good for online games or video or voice conferencing.

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Below:  The tube containing the tub and with the trusty flexible stalk suction cup that I find so useful!

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The radio USB socket is the only part open to the elements and could be shrouded if necessary.

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Add a bit of bubble wrap to stop it all rattling around...

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One finished USB Cantenna!

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