Cookie Cantenna with Funnel
by Daniel Marsh dmarsh@speakeasy.org
This article will describe how to make a cheap, portable, high performance (15-18 db) directional antenna out of commonly available parts that can be purchased in most grocery and hardware stores.
Background
Until recently I , people seeking high performance antennas have either had to put up serious money for commercial antennas or attempt to create their own out of scavenged parts. This has lead to a whole slew of novel designs ranging from the PringlesCantenna to the MicroTVAerial. Most homebrew designs are compromises of one sort or another. With the PringlesCantenna, you sacrifice performance and weather resistance to be able to occasionally see a friend gape "you made that antenna out of WHAT?" With the MicroTVAerial and other more engineering intensive designs you get good performance at the cost of difficult assembly, often requiring specialized tools. Some antennas, like the SlottedWaveguide almost necessitate the use of milling or laser cutting machines. Unlike these other designs, the CookieCantenna aims to let you have your cookies and eat them too!
Chief Goals
- Low cost ($10-15 max)
- High Performance
- Easy parts acquisition
- No use of tools that are hard to find
- Portability, as well as suitability for longterm mounting.
- Eat cookies
Needed Parts and Tools
Parts
- 1 - 4" diameter Pepperidge Farm Pirouette Cookie Can
- (available at almost any supermarket for $4-$5). Reportedly, Trader Joe's has a similar cookie can for $2. Also reportedly, Dollar Stores have a similar cookie can for $1, with cookies.
- (available at almost any supermarket for $4-$5). Reportedly, Trader Joe's has a similar cookie can for $2. Also reportedly, Dollar Stores have a similar cookie can for $1, with cookies.
- 1 - chasis mount female N connector, preferably the type that mounts with a single large nut. An example is shown here:
If you are in the Seattle area, Vetco Surplus has them for about $3 each
- 1 - short piece of 12-14 gauge bare copper wire (5" should be more than enough).
- 1 - Washer with an inner diameter of ~5/8 inch
- (enough to just clear the threads on the N connector)
- 1 - 4 inch to 6 inch heating duct adapter available from most larger hardware stores
Tools
- Can-opener, preferably the electric type that "peels" back the lid
- Soldering iron and solder
- Measuring ruler with millimeter scale
- Drillpress, dremel or some other tool that can cut through thin metal
- Crescent Wrench
- Possibly a file
Assembly
- Take off the lid and remove all the cookies and packaging. The interior should be relatively clean, but you may want to wash and dry before proceeding.
- Use a can-opener to remove the bottom of the can. The lid of the can is totally flat, so does a better job of reflecting radio waves without distorting them. The bottom of the can has small ripples for strength, which seem to add a small amount of distortion. So, for our purposes, we are going to remove the bottom and use it as the opening into the waveguide. If you don't have one of the fancy electric can-openers that will remove the bottom without leaving sharp edges, you may need to use a file to remove any sharp edges or protrusions into the can's interior.
- You now have a hollow cylinder. Pop the lid on one end of the cylinder and measure 44 mm down the cylinder lengthwise from the spherical plane of the lid and make a mark in the paint with a sharp object. It is important to measure from the face of the lid and not simply from the end of the hollow cylinder, as the two resulting distances are slightly different and could negatively impact antenna performance.
- Drill or use some other tool to create a hole for your N connector, centered on the mark you made in the last step. The hole should be just big enough to allow the threading on the N connector to get through. In my case, this hole ended up being about 5/8" in diameter, but yours may be slightly different. Try to avoid deforming the shape of the can during this process. If the hole has any rough edges, use a file to smooth them down.
- Next, get out your N connector and copper wire and plug in your soldering iron. Cut a piece that will be a little long for our purposes, say 40mm worth and solder the wire into the center tap of the N connector. It may be difficult to keep the wire straight and solder at the same time, so you might want to get a friend to hold the wire in place (ideally with needlenose pliers. The wire will get hot!) while you hold the soldering iron in one hand and the solder in the other. A picture of one style of N connector with a wire soldered in place is shown below for reference.
- Now that your wire is in place and sticks out straight, you will want to trim it so that the total length of the wire and the brass nub you soldered it into is 31 millimeters. READ THIS AGAIN. You want the total extruding length of the brass nub + copper wire to be 31 millimeters. Here is another diagram to help:
- You now get to insert your brand new N connector/copper wire combo into the hole you made. We want as little of the connector itself sticking into the interior of the cylinder as possible. My connector ended up having a lot more threading than needed. If I had just stuck the connector in and bolted it in place, I would have ended up with a sizeable chunk of connector inside the cylinder interfering with all those radio waves that are supposed to be bouncing around. My solution was to slip a washer over the connector BEFORE inserting it into the hole so that just the bare minimum of threading needed to tighten the nut in place extruded into the interior of the cylinder. The size of the washer, if needed, will depend on the connector you buy. You may want to drill your hole and make your connector/wire parts first, then take the two down to a hardware store and figure out the proper size to get.
- Take the lid off and start threading the nut in place. Once it is started, use a crescent wrench to tighten the nut in place.
- Congratulations, if you have gotten this far, you should have a fully functional 15 db directional antenna. With a few additional steps and pieces of hardware we can increase the gain and add some weatherproofing (if you plan to mount it outdoors longterm).
Funnel Cone Addon
- By adding a metallic funnel we can increase the performance of the antenna by as much as 3 db (double the signal strength). This added performance may double the cost of your antenna to as much as $12, however! I was able to create a funnel for my antenna out of a 4" to 6" heating duct adapter that I found at Lowe's Hardware for about $4.25. Our can is close enough to 4", that it slipped on the end with no trouble and was tight enough that it wouldn't come off without a sizeable tug. I plan to epoxy my funnel on once I get to thinking about mounting my antenna outdoors long-term.
Suggestions for Weatherproofing/Long Term Mounting
- Take some epoxy and glue the lid in place. Once the epoxy has has set, drill 4 small holes at 90 degree arcs around the sides of the lid (the hole should go through both the side of the lid and side of the cylinder). This should provide drainage for any water that condenses or somehow gets into your can, regardless of how you have your antenna oriented.
- Make an endcap for the open end of your antenna out of some sort of material that is microwave transparent. In short, we want the 2.4 ghz radio waves to be able to get through this cap, but not the rain. Most people use some sort of plastic lid from another can for this purpose. You can test if your cap is microwave transparent by putting it in...you guessed it, the microwave. Nuke your cap and a cup of water (to prevent the microwave from overloading) for a minute or two. If your cap is still cool, then it is transparent to microwaves and you can attach it to the open end of your cantenna without losing much signal strength.
- Your Cantenna is made from steel, which can rust. Paint the exterior of your antenna with some good rust-protecting paint. Avoid getting paint on the connector itself by wrapping it in electrician's tape before painting.
- Water could potentially get into the cable through the connector, so once your cable is attached to the antenna, use some heat shrink tubing and some non-corrosive sealant to make sure no water can get in your cable ends. One reader wrote to inform me that silicon sealant leaks acetic acid while it cures. I personally have not had a problem using it in the past, but ymmv. The same reader suggested an alternative. Radioshack sells some stuff especially for connectors at around $4 for a small tube. If you plan on using more goop in the future, you can buy the same stuff in the form of "windshield sealant" at most auto supply stores.
- Hand holding this antenna is awkward and about the only thing to hold onto is the connector/cable. Holding onto the connector works in a pinch, but ends up causing wear and tear on the connector and may loosen the nut that holds the connector in place. Drilling into the can to mount a handle is not advisable, as anything inside the waveguide will cause distortion. My solution was to take a strip of sheetmetal and bend it around a similarly sized can (don't use the cookie can for this, as it is thin walled) until I had a circular shape with two flat strips sticking out perpendicularly.
I glued some thin rubber strips to the inner surface where my circular mount would contact the cantenna. This provides a lot of friction and keeps the mount from slipping. I used my drillpress to drill holes through the flat sections that stick out from the circle and then used nuts and bolts to tighten the circle around the cantenna. I then attached a makeshift handle made out of a scrap piece of sheet metal. There are a lot of ways that you could potentially mount this antenna. I like mine as it is easy to construct and doesn't alter the antenna in any way. It shouldn't take much effort to adapt this mount for more permanent installation.
Links to Similar Designs
PringlesCantenna as made from a Pringles container
Non-author Comments
A commercial version of a "cantenna" with an integral camera tripod mount is at: http://www.cantenna.com. While it doesn't come with cookies, it does cost under $20. The amount of gain isn't indicated at the website. They didn't answer my email request about how much gain in dB their antenna has. It would be embarrassing if their cantenna had less gain than a Pringles cantenna!
This is the end, for now. You can go back to your boring life, or go out shopping with an excuse to eat cookies!
Works good in Visalia!
MichaelPierce: If you are interested I have a one that I bought a while ago to try it out. I'll bring it to the meeting if you want and you can run some gain tests on it. email me at Michael at piercedesigns.com
I just looked at the Cantenna website (http://www.cantenna.com/answers.html) and they say: Electrical Specifications Frequency: 2400-2500 MHz Gain: 12 dbi Beam Width: Approx. 30 degrees Impedence: 50 Ohm Max input: 50 Watts VSWR: <1.5:1 avg.
Mechanical Specifications Length: 12” Material Base: Metal Lid: Plastic Connector: N Female Polarization: Linear
Looks like a little less gain than the one described right here, but still decent.
-Haudy Kazemi
Chew Carefully !
Down here in Portland OR a bunch of us met up to make various DIYtennas. I picked the cookie can one because..well because they taste so damn good. That they got better results than folks futzing with salted potato products was just more the reason.
I built a few of them and mounted one on a retractable 10 foot pole for site survey fun. http://www.personaltelco.net/gallery/view_album.php?set_albumName=album12
Given the simplicity of the design, the fast production time and the results in db gain I have gathered up the makings for about 6 more. They make the perfect gift for the wirelessnut who has everthing.
Thanks for the great design
-tomwsmf http://www.personaltelco.net/index.cgi/TomHiggins
Working on my own version of this antenna. The Home Depot has various size stainlees hose clamps that work nicely to hold the two sections together. I also found a great "radome" for this antenna. Look at the mixing buckets in the paint section. One of them fits perfectly over the 6" duct adapter. It can be held in place with another hose clamp.
-sean
I have more than a year of experience with this exact cantenna. Its a functional design and thanks for posting the how-to. A word of caution to others, the funnel does absolutely nothing to improve signal strength. Of course my card (Senao 2011 CD Ext 2) and driver (sourceforge WirelessDriver and Kismac) contribute to that opinion. Anyway, if you disagree with me, you can buy the stove pipe at the plumbing supply on the west side of Stone Way in Seattle. I have two extras that I wont be needing.
Also, I was persuaded that the shorter the pigtail the better. In fact, I got a 5 foot pigtail and used it for a year, then I cut it in half in hopes of a better signal. The shorter 2.5' pigtail is no better than the 5' pigtail (I even shielded the short pigtail better than the original.).
Its time to take this cantenna design to the next level.. any ideas, innovations? Seems like an adjustable metal aperture would be a good addition based on my testing.
Update: upgrading to the 2511CD Ext 2 (SenaoCard) certainly helped to improve signal strength! -Chris
The "funnel" should improve the signal, but there is an optimum shape, and it has to be done right. That means it must be electrically attached, not just glued or taped on. Solder it on! As far as the feedline, there isn't enough loss on 5' to make a big difference by cutting it in half. If you had 15 or 20' of small coaxial cable, then it would. -Andy N7TP
I want one! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 10/13/2005 question Has anyone tried sticking a USB adapter in a can? Any suggestions on where to place it (diameter)? --steve
http://www.nodomainname.co.uk/cantenna/cantenna.htm Is a link where a guy put a can over his usb adapter antenna and improved his reception.
-duke
I just made one of these this past weekend and i got around an 18+db boost with this!! Yes, the funnel works perfect, i did what the other guy said and i soldered on, hell, i pretty much soldered everything on. It looks fugly as hell because solder does not stick well to piroutte cans since its polished up and i went overboard on solder because of that but it has an awesome gain for what its worth.
-Vin
Check Walgreen's (in the U.S.) for Royal Dansk "Taste To Remember Luxury Chocolate (or Vanilla) Wafers". Same size/shape can as the Pirouette. Currently (as of 1/3/07) $2.99 or 2 for $5.
-Rob
Before I found this page, I built 2 using the Pirouette cans and one using a candy can from City Club. The cans are all the same size. I purchased the Pirouette can in Maui and it was almost $4.00. The City Club in Lapaz Baja had two cans for $5.00. In Mexico they have a coffee can that is the same size also. Now for a question. Has anyone tried connecting up two of these cans with a splitter to see what they get? I have done regular can antenna built with BNC connectors and a 50 ohm Y. This is not optimum but it was what I had. Here is a link to the pictures and Netstumbler plots. http://windsurf.mediaforte.com/wifi/wifi_antenna.html
-Wilton
I built one of these and came back to check to find that it had been spammed over. Great work! -Brett
I just came back from the www.cantenna.com website. Purchase a 12dbi cantenna for $40??? I don't think so. You can get a professional parabolic (or yagi) antenna of 20dbi or more for that kind of cash. -Stephen P
