We started out using the traditional method of building a Cantenna, using the sites provide in the class assignment Case Study 04 – Wireless Antenna Project. And the decided to use the idea of waveguide signal and incorporate it into our design.
History:
The term ‘Cantenna’ originally referred to a product sold by Heathkit Co. in Benton Harbor, MI, USA. It was a 50-ohm resistive load used by radio amateurs. However, in more casual vernacular of the Do-It-Yourself community, it has functionally become a portmanteau of can (i.e. an empty can) and antenna, since they’re used to broadcast (and receive) signals, and not just terminate them.
Facts:
A cantenna is a directional waveguide antenna for long-range WiFi and can be used to increase the range (or snoop) on a wireless network. The original design was based on a Pringle’s® Potato Chip can, a cantenna can be made from a variety of cans, bottles, or boxes. The materials to build one can be purchased online or at an electronic supply store. The original design employed a Pringle’s can, but for the best possible design many sites recommend using a longer tin can, or adding an extension.
While cantennas are useful for extending a local-area network (LAN), the miniature design makes them perfect for mobile applications, such as wardriving. Its design is so simple and ubiquitous that it is often the first antenna that WiFi experimenters learn to build. Even the Secret Service has taken an interest in the can antenna.
So here’s where we Start!
Equipment need:
- One can (48 oz Safeway Chicken broth)
- A can opener
- Drill press
- Metal file
- Center punch
- Tape measure
- Small tripod
- One N type female RF connector (radiator)
- 1 Pigtail (N-type male to your style jack)
Measurements:
- Diameter of Can 4.25 inches or 11.1 mm
- Length of Can 7 inches or 17.5 mm
- Distances of hole from bottom 1.63 inches or 41.1 mm
Interesting suggestion: (might have tried this variation if I’d found it in time)
If the bottom of the can is not smooth a extra bottom can be added inside the can. It can be made from tinned steel or aluminum which is cut according inside diameter of the can. How it is mounted inside the can there are countless means. It is not necessary be tight, microwaves are not passing through narrow slots. Between the extra bottom and original bottom there becomes a space with no need.
My contributions:
- Researched various websites to help determine the ideal dimensions of a can to receive optimal signal strength.
- Purchased a 48 oz can of Safeway’s Chicken Broth.
- Remove one end and clean thoroughly, and removed the label.
- Measured the diameter of the can inches and used the site Rudy provided to calculate the proper placement of the hole for the radiator. Since it was difficult to determine in where 1.63 inches, I found a calculator online that would convert inches into centimeters.
- Used a center punch to mark the correct point to drill, and used a small file to create a pilot hole.
- Drilled the 5/8 inch hole in the can with a drill press.
- Installed the radiator into the can.
- Tested can on Friday May 29th.
- Added additional 48 oz can and Taped together with metal duct tape, to see if we could get a stronger signal (less noise)
- Tested Saturday May 30th.
- Removed second can because it caused the signal to worsen (more noise)
- Masked off the radiator, and painted the can.
- Decorated the can.
- Took pictures.
- Photoshoped pictures.
My Partners Contributions:
- Researched various websites to help determine the ideal dimensions of a can to receive optimal signal strength.
- Measured diameter of can and measured for placement of pilot hole for radiator.
- Added additional 48 oz can and Taped together with metal duct tape, to see if we could get a stronger signal (less noise).
- Tested Saturday May 30th.
- Removed second can because it caused the signal to worsen (more noise).
- Took pictures.
- Photoshoped pictures.
Final result of Cantenna:
I tested our cantenna on Friday May 29th and the test result was a signal 75 at around 310 feet. The next day, Saturday May 30th we had add an additional 48 oz can to lengthen the cantenna in the hopes it would strengthen our signal, unfortunatly this did the opposite the signal was 88 at 310 feet. So, we remove the second can and retested. This second test on Saturday May 30th was much better, we tested at signal strength of 79.
The Final Product!!
Decoration supplies needed: (fortunately I had supplies on hand already)
- Hot glue gun and glue sticks
- Masking tape
- Can of spray paint
- Google eyes
- Pipe cleaners
- Craft foam
- Scissors
- Florist wire
Interesting Tip:
Because the Super Cantenna has linear polarization, you may find that you get a better signal by rotating it slightly clockwise or counterclockwise on the tripod along its cylindrical axis.
Cantenna/antenna technology: (I found this on a site, obviously understand just fraction of what it’s explaining).
There are three different wavelengths in the waveguide tube. Here they are marked as Lo, Lc and Lg.
Lo is the wavelength of the hf signal in open air or Lo/mm = 300 / (f/GHz).
Lc is the wavelength of the low cut frequency which depends on tube dia only Lc = 1,706 x D
Lg is standing wavelength inside the tube, it is function of both Lo and Lc
A waveguide which is closed on the other end acts similar as a short circuited coaxial cable. The coming hf signal reflects from ending point and there forms so called standing wave when incoming and reflecting signals in different places are either weakening or amplifiering each others:
If there is a measuring probe which is moving in axial direction inside the tube there can be found some minimum and maximum points in certain intervals. At the closed end the signal is zero and so will be in halfwave intervals. The first maximum point is quarterwavelength from the closed end. This will be the best place to outlet signal to coaxial line. You can notice that maximum area is quite flat. So the place of the outlet must not be very accurate.
It is important to notice that the standing wavelength Lg is not the same as wavelength Lo counted from hf signal. Large tubes are near as open air where Lg and Lo are almost same but when tube diameter becomes smaller the Lg increases effective until there becomes a point when Lg becomes infinite. It corresponds the diameter when hf signal doesn’t come to the tube at all. So the waveguide tube acts as a high pass filter which limit wavelength Lc = 1.706 x D. Lo can be calculated from nominal frequency: Lo/mm = 300/(f/GHz). Inverse values of Lo, Lc and Lg forms a right angled triangle where becomes the equation of Pythagoras:
(1/Lo)2 = (1/Lc)2 + (1/Lg) 2
which can be solved
Lg = 1 / SQR((1/Lo)2 – (1/Lc)2)
In the antenna the N connector is situated in maximum point or length of Lg/4 from the closed end. Total length of the tube is selected so that the next maximum place hits on the open end of the tube or 3/4xLg from the closed end. The latter is only supposed by my own and found be not the worst decision.
What I learned:
It’s something that was brought up in class. Someone asked about putting a cap or lid on the end of a cantenna. The wanted to know what the effects would be to the signal strength. What I found out was the is a way to test a lid or ‘End Cap’ to see if the plastic is microwave-transparent. If it isn’t you will lose your signal.
Here are the methods I found for testing an ‘End Cap’:
Method 1:
With a microwave oven – fill a mug half-full of water, and place it in the oven along with the plastic end cap. Just lay the end cap down on the rotating table, don’t let it touch the mug. Cook on full power for one minute. I forgot to say, put a teabag in the water first… Take out your mug and plastic cap. The water should be hot, but the end cap cold. If the cap is warm then it cannot be used, since it is absorbing microwaves.
Method 2:
With no microwave oven, but an open-scanner boat radar available – tape it to the front of the radar antenna, and run the radar. Run it for a couple of minutes; the effect is about the same as with the oven. A Radom-type scanner won’t work; as it isn’t putting out enough juice in the short time the beam hits the end cap, once per rotation.
