- The 2nd antenna a Can-Type -
The 2nd Antenna is a 'Can-Antenna', or 'can-tenna', in technical terms called a 'Wave-Guide Antenna'. An SMA-type Female Chassis-mount connector is used. The can diameter is about 90 mm for the 2.4 GHz band. It can be constructed e.g. from old coffee tin can. Nowadays I haven't seen these in stores but maybe somewhere they can be found. The can diameter has to be between 80 and 100 mm, side and bottom must be smooth and direct. Be careful not all cans are straight, but ribbed, these are no good. If there are some burrs on the open end they have to be smoothed out e.g with a hammer or file, being careful not to deform the can.
On the diagram below the diameter of the can is D in mm and length is Lg in mm. The best length is 3/4 of Lg, But this is not critical, so anything between 3/4 of Lg and Lg would be ok.
Lo would always be 31 mm, measured from the can to the top of the conductor.
Lg/4 is very critical and alterers with the diameter, length and frequency. On a 100 mm can the Lg/4
is 44.2 mm, and on an 85 mm can is 57.8 mm, measured from the base of the can to the conductor.
The making of your Can-tenna
Making anything above 50 MHz requires a measure of skill. Generally the higher the frequency the higher the skill. You can imagine that half a mm on the 2.4GHz band might change the frequency over 100 MHz, rendering your work unless. To measure such minimal amounts of mm, I cut down a 6 mm aluminium rod, to the right size. Now it was easy to drill a hole in the right place. Drilling first a 3 mm hole, then working up to 6 mm or 8 mm. You don't need to drill out the hole to 12 mm, the size of the connector as it would be mounted on the outside of the can, as in the picture above. Make sure that any deformation is tapped out with a little bodywork hammer. The SMA-type connector assembly is then soldered in place to the outside of the can.
| Size D in mm | Lg Total length | 3/4 length of Lg | Lg/4 in mm |
|---|---|---|---|
| 85 | 231.3 | 173.5 | 57.8 |
| 86 | 224.8 | 166.6 | 56.2 |
| 87 | 219 | 164.3 | 54.7 |
| 88 | 213.8 | 160.3 | 53.4 |
| 89 | 209 | 156.8 | 52 |
| 90 | 204.8 | 153.6 | 51.2 |
| 91 | 201 | 150.7 | 50.2 |
| 92 | 197.4 | 158.0 | 49.3 |
| 93 | 194 | 145.6 | 48.5 |
| 94 | 191 | 143.3 | 47.7 |
| 95 | 188.4 | 141.3 | 47.1 |
| 96 | 185.8 | 139.3 | 46.4 |
| 97 | 183.4 | 137.5 | 45.8 |
| 98 | 181.1 | 135.8 | 45.2 |
| 99 | 179 | 134.3 | 44.7 |
| 100 | 177 | 132.8 | 44.2 |
(Round up and down e.g 141.6 = 142 - or - 128.3 = 128)
Materials
1x SMA-type Female Chassis-mount connector (If connector is Nickel plated then it must be brass based or solderable).
1x USB WiFi wlan card with SMA Connector and all the Channel 1 ~13, EU Norm, from *bay UK. I use a Proxim Orinoco Gold PCMCIA card expensive but very good, about £90 from *mazon in the uk.
3m of good quality 50 Ohm coax, like RG8 with 2 male SMA connectors.
1x Straight tin can, not the ribbed ones, about 90 mm in diameter.
Soldier, drills, about 50 mm of 2 mm diameter copper wire, a 150 Watt soldiering iron.
Using my antenna on a broom stick I was able to connect to the laptop of my friend about 10km away with little problem. On the web is to read that the beam would be about 30°, I can say that this was my view as well, so very directional. In September 2007 I was able to do a long distance test with another radio amateur DL4BQ near Leer, north Germany, a distance of 36km away, the signal was just readable. But for working over a camp site, a lot have free hot-spots now, would be fine. I have used mine last year all over France, once on the car park of Leclerc. As you can imagine I got a lot of looks, as if I was ET.
Best of luck building, testing and using your home-brew can-tanna.
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