Now that you have finished drinking that last tasty cup of coffee, what do you do with the empty coffee can?
Go Wireless! That's what.
Here is an easy to build, accurate and powerful wireless antenna made out of an empty 13.5oz coffee can. Some soldering experience is required to build this project but if you can wield a soldering iron and a roll of solder, you can't help but turn out a well built antenna for long range wireless communications.
Step 1: Parts and Tool List
To enjoy great wireless, you will need at least one antenna. If you are planning to create a short haul project between two locations, make two antenna so you have a matched set.
1) 13.5oz Maxwell House or any other brand tin can with plastic lid. (Empty of course).
1) 4 inch by 4 inch sheet of brass or tin.
1) 1 inch long by 1/4 inch diameter Brass tubing. (Any model or hobby shop).
6) feet of AIR195 low loss 50 ohm coaxial cable. (Available from air802.com. RG-58 may be substituted with marginal results).
1) SMA Female connector. (For connecting to your bridge or antenna jack. Available from air802.com)
1) Brass angle bracket. (Local hardware store).
1) 1/4-20 Brass hex nut. (Same hardware store).
30 to 50 Watt Soldering Iron
Solder Flux (zinc chloride or rosin type. not acid flux)
Coaxial cable connector crimp tool for 1/4 inch cable.
Drill with assorted drill bits
Black spray paint
RTV Silicone Rubber compound or Clear Silicone Bathtub Caulk
Sheet metal sheers
'0000' Steel wool
Step 2: Calculations and Layout
Some Googling on the internet produced a number of Cantenna calculating tools. I chose this one because of its ease of use.
Any can will do but when you plug in the numbers you might find that you need to cut the can to the correct length before using it. The 13.5oz. coffee can is just right and works with no cutting required.
The frequency required is 2.437 GHz (or wireless channel 6) and the diameter of the coffee can is 3.875 inches or 98.4mm.
When you plug these numbers into the calculator, the length of the can is .75 x Lg or 135.75mm which is the exact length of the 13.5oz. coffee can!
Here is the layout with all the necessary dimensions.
NOTE: These are not exact dimensions but are close enough to give you results that rival the manufactured cantennas.
Step 3: Preparations
Prep the can by removing the label and any remnants with alcohol or any adhesive remover.
Cut the ends from the can with a can opener.
Drill a 7 mm diameter hole 45 mm from one end of the can.
Wash the can thoroughly and dry.
Use steel wool to polish the end of the can which has the hole drilled in it.
Set the can aside.
Using '0000' Steel wool, polish the brass tubing so solder will take to it.
Cut a 30 mm long piece of brass tubing from your stock and set it aside.
Prepare one end of the cable by removing 60 mm of the outer jacket.
Cut the shield braid to 20 mm long, fold it back over the outer jacket and unbraid it.
Remove the center conductor insulation down to the shield.
Measure from the shield to the end of the center conductor and cut the center conductor down to 31 mm.
Set the cable aside.
Use '0000' steel wool to polish both sides of the brass and set it aside.
Step 4: Solder Tubing to Can
Push the brass tubing into the hole drilled in the can, allowing only 1 mm to protrude into the can.
Flux the joint where the tubing and the can touch.
Wrap a piece of solder around the tubing creating a ring. Slide the ring of solder down onto the joint and melt it with the soldering iron.
Let the joint cool and repeat the soldering procedure on the inside of the can.
Using an acid brush, clean the joint inside and out with alcohol to remove any flux from the work.
Make sure your solder joint is shiny and new looking. A frosted or pitted look means that the joint wasn't hot enough. Reheat the joint and apply a touch more solder to fix it.
Step 5: Solder Can to Brass Sheet
Flux the end of the can closest to the tubing and flux the edge of the brass sheet.
Place the brass sheet on a fireproof surface and place the can on top of the brass sheet.
Solder the can around the inner and outer circumferences.
Set aside and let cool.
SOLDERING TIP - Use Silver solder in paste form to create a clean joint without having to mess with flux and solder.
Cut away any unneeded brass, file or sand even with the can edge.
Clean up your work with alcohol to remove dirt and flux.
Step 6: Solder Mount to Can
Turn the can onto its side with the brass tubing pointing straight up. Brace the can between two wood blocks to steady it.
Locate and place the brass bracket toward the outside edge of the can in line with the tubing.
Flux the bracket and can then solder the bracket to the can in line with the tubing as shown.
Let the can and bracket cool then clean with alcohol.
NOTE: A heat gun may give better results and provide better heating to the workpiece. Use rosin core silver solder for the best joint.
Step 7: Finish the Mount
Drill a 8 mm hole in the brass bracket
Flux the area of the hole and clamp a 1/4-20 brass nut in place over the hole.
Solder the nut to the brass bracket.
The mount allows the cantenna to be attached to a tripod for accurate aiming.
Step 8: Clean Up and Paint
Clean the can and bracket in alcohol to remove all flux and dirt.
Sand or file all rough joints and edges.
Mask off the brass tubing using masking tape.
Paint the outside with Black Rustoleum enamel. Do Not paint the inside.
Let dry for 24 hours before completing assembly.
Step 9: Cable Assembly
Remove masking tape from the brass tubing.
Push the cable into the brass tube until the center conductor insulation is even with the inner edge of the tube and only the center conductor is visible in the can.
Using the crimp tool, crimp the brass tubing around the coaxial cable to secure it.
Finally, apply RTV Silicone Rubber Compound to the inside rim of the plastic coffee can lid and snap onto the front of the antenna.
Let the assembly dry before proceeding with the next step.
Step 10: Connection and Use
Prepare the other end of the cable and crimp on the appropriate connector for attachment to your laptop, bridge or router.
Here I'm using an SMA connector for my mini bridge which will connect to my laptop.
To bypass the bridge, you could modify your laptop and add an external wireless connector like I did in the photo below which will allow you to connect the antenna directly to it. (I'll post an instructable on how to modify your laptop soon).
Step 11: Create Your Own Communications Channel
Short Haul Wireless
With two antennas, a wireless access point and a wireless bridge, you can create your own short haul network. Short haul wireless paths can be as short as 150 feet or as long as several miles.
Since there are 11 wireless channels to choose from, you could build several 'repeaters' and create a network up to several hundred miles. A repeater consists of two antennas, a bridge and an access point. The receive side or bridge side might operate on wireless channel 3 and the access point side might use wireless channel 9. In this way, you would avoid any interference between the two signals. With the correct selection of wireless channels to reduce interference, you could conceivably build a network around your entire city!
With the addition of a network switch, you could tap the network and use it as your internet connection. Check you local township ordnances as well as your contract with your internet provider for possible restrictions before launching a network building program between you and your friends.
The diagrams below illustrate the three short haul schemes that are possible.
Figure 1 shows a short haul network with an extended user.
Figure 2 shows a short haul network with an unattended repeater.
Figure 3 shows a short haul network with a split user and extended user.
Good luck and happy connections!