Better Pringles Can Antenna
The O’Reilly & Associates book ‘Building Community Networks’ has popularised the Pringles Can antenna. The pringles can is aluminium lined can 230mm long, with an internal diameter of about 70mm. This is not ideal for a 2.4 GHz antenna, and is better suited for 3.1 GHz under the design from the ARRL.
Designs for the Pringles Can require a dipole just shorter than the centre of the can to be inserted 86mm from the closed end of the can.
λ = 3.0 x 108 x (1 / 2.462) x 10-9 λ = (3.0 / 2.462) x 10-1 λ = 0.122 meters 1 / 4 * λ = 30.5mm
The published design calls for five 1″ washers to be placed on a continuous screw inside the antenna, with each washer being kept apart by some fine
aluminum tube. This tube is so fine that it will deform easily if you tighten the nuts too tight. Cutting the stuff is not easy either, and it is not cheap. Apart from cables and connectors it is the most expensive part of the whole design. So get rid of it. Do not use it!
There are better things to keep the washers in place. They are called nuts. And they were designed for the purpose
|A small nut on each side of the washer will keep it in place and will make adjustments easier. The washers need to be placed about 30.5mm apart. This should be measured from one end, so that measurement errors are not multiplied. Nuts are also much cheaper than the Aluminium tube.|
As far as I can tell the washers just set up a series of cavities where the microwave signal can resonate. Again I do not think that the washers are the correct size. I would imagine that they should be about 30mm in size too. About the only thing that is correct about this design is the seperation of the elements. The spacing lines up to about every 1 / 4 * λ
The issue then becomes tuning the antenna for the best results. The reason for this is that minor changes in the injection point will move the tuning. Tuning is non-orthoginal, meaning that moving one washer will affect all other washer positions. Get it good and dont touch it again. Dont even think about adding one washer at a time – it does not work that way.