The Conetenna - a wi-fi antenna

Step 5 The Cone

This is what I felt was the most important part. Building the cone. I did this last so that any last minute inspiration might have a chance to indicate how I was going to make this part.

I finally decided to use a sheet of UHMW polyethylene that I had kicking around, and just cover the outside with aluminum foil. I just didn't feel like using the aluminum panel I've been saving for an oil pan project.

First I used some software to determine the length of the cone based on what the exit opening was going to be and the opening of my feed-can. Then I drew that in Deltacad to find what the short and long radius needed to be to lay out a pattern on the plastic sheet.

The can is 83 millimeters in diameter, the exit diameter 242 mm, so that worked out to a layout radius of 4.5" & 13"

Using Deltacad, I figured that the amount of the layout arcs I had drawn, needed to measure 23" point-to-point on the outer radius. The plastic sheet just happened to be 23" wide, so I measured to the exact center of the sheet before drawing my arcs, and just drew them all the way to the edges. Not having any better tool, here I can be seen using a tape measure to make a mark every inch along the 13" radius. The 4" radius was drawn with a compass. Then I connected the marks and used scissors to follow that line. I took a close-up photo of the paper you can see in the background, that's my notes for this project. This will show what I mean about the dimensions of the cone.

Comments

[saysay]

what is the purpose of the cone in your conetenna?
what are the specs of it??

[Shadetree Engineer]

The cone helps get more signal into the waveguide.  It acts as an impedance matching device to free air.  The dimensions are calculated with the help of some radio frequency tuning software, basically the bigger the opening, the longer the cone.  The ratio follows a complicated set of rules so it doesn't really just scale up by doubling the measurements.  Seeing as this waveguide is not really the best choice, I may as well have used a dog cone. i would recommend using one of the coffee can designs instead of a fire extinguisher.  It looks like I didn't put the finished length of the cone into this Instructable, but I did put the diameter of the cones exit - 242 mm. The antenna isn't nearby or I would just measure it and say what the length of the cone is, sorry.

[the_burrito_master]

just get a dog cone lol that might work.

[the_burrito_master]

oh he already said it down there. :P

[Grey_Wolfe]

For those of us who do not possess the appropriate programs to figure out the curves for the cone, and are either to lazy or simply do not know the formulae to do it by hand, a good option is an Elizabethan Collar. These are available at most pet retailers, (you know those cones you put around your dog's head to keep him from gnawing on the goods after getting fixed) and they are very affordable, $8-10 USD for the largest sizes. Also, they are fairly rigged, so should hold up quite well. And, they come in designer colours. :-P

[Shadetree Engineer]

I knew I should've put in some dimensions! The dog collar-cone thing will help add signal to a can, but I think it wont be as directional. However, that is a good approach for quick construction if you wrap some foil around it like I did. I'll add some specs on my cone if I can get into the edit mode...