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Coffee Can or Pringles Can?
This wi-fi antenna design is a much simpler DIY project than the pringles cantenna. Basically there are 3 parts to a build-your-own 2.4 Ghz cantenna kit: a pigtail, an N-female connector and a metal coffee can. A smooth metal can is better, because irregular surfaces, such as ribbed cans, can cause internal reflections and scatter radio-waves.
The coffee can antenna is a waveguide/feedhorn, which can be used by itself, or in combination with a parabolic dish for greater gain/distance.
Size and shape of a microwave waveguide (the coffee can) and the placement of the radiator inside the waveguide is important. The 5.25 inch/133mm long coffee can (4 inch/102mm diameter) antenna is made by following the steps below.
Drill a ½ inch/12mm or five-eights inch/16mm (depends on the N connector) hole in the side of the all metal can for the N connector. You can drill multiple-size holes in thin sections of metal, plastic, and wood using a single step bit. The posititon of the N connector hole is determined by the overall diameter of the can. Measure up from the inside of the can.
- 4" diameter, hole is 1.72" from bottom
- 3.75" diameter, hole is 1.85" from bottom
- 3.5" diameter, hole is 2.07" from bottom
- 3.25" diameter, hole is 2.5" from bottom
- 3" diameter, hole is 3.75" from bottom
- 101.6mm diameter, hole is 43.7mm from bottom
- 95.25mm diameter, hole is 47mm from bottom
- 88.9mm diameter, hole is 52.6mm from bottom
- 82.6mm diameter, hole is 63.5mm from bottom
- 76.2mm diameter, hole is 95.25mm from bottom
Insert and solder a 1.2 inch/30.5mm piece of 12 gauge solid copper wire (1/4 guide wavelength size) into the N connector to serve as your driven element (radiator). A piece of brass rod will work as well. The wire side goes in the can. The other side, where the cable attaches, goes outside of the can.
N-Female chassis (panel) mount connector
The N connector, one of the first connectors capable of carrying microwave-frequency signals, is a threaded RF connector used to join coaxial cables. Solder (preferred), epoxy glue or use screws to attach the N connector/element assembly fitting to the can. Optional: Drill a small hole in the can just behind the N-type connector. Rain or condensation which finds its way into the can has an easy route out. The hole should not affect the performance of the cantenna.
Attach the N-Male end of a pigtail (pictured below is a 60 inch MC-Card to N-Male LMR100 Type cable) to the N-Female panel mount connector on the can and the other end of the pigtail to your nic (wireless network card). Ready-made pigtails are available from the advertisers on this site. Important: Unless you already have a wireless networking card with an existing jack for an external antenna, you will need to either modify your particular card by taking it apart and modifying it with delicate, skilled soldering to attach an antenna jack (voiding your warranty), or consider buying a new/used card that already has a built-in jack.
Some common pigtails are:
- MC Card to N-male for use with Orinoco, Proxim, Avaya wireless, Toshiba, Enterasys, Buffalo and others.
- MMCX Plug (male) to N-male for use with Cisco, Samsung, Symbol, Zcomax, 3Com and others.
- RP-SMA Plug (female) to N-male for use with Linksys, Dlink, US Robotics, Zcomax, Zoomair and others.
- RP-TNC Plug (female) to N-male for use with Cisco, Linksys, SMC, US Robotics and others.
When aiming the cantenna, the polarization is important. Polarization refers to whether the driven element inside is pointing skywards (vertical) or sideways (horizontal). The direction of the driven element should match the antenna it is communicating with. In other words, the plane of polarization is the same as the N-connector's that the "pigtail" cable connects to. Some users rotate their antenna at a 45° angle, giving it a mixed or split polarization. This might work better because the target antenna may not be on the same absolute plane as your antenna's mounting plane. A tripod is handy for mounting an antenna.
It's a probably a good idea to always point a cantenna away from you, even thought the power output is relatively low. Remember the can is a focused microwave device. More about health concerns here.
That's all there is to achieve a 10db or better gain at 2.4GHz. The coffee can design is simpler and easier to make than the pringles cantenna. Use either a high-quality female bulkhead (round) Type-N connector or a chassis/panel (square) Type-N connector. For an additional 5dB of gain use hardware cloth available at a hardware store to form a funnel 4"/102mm at the throat and 16"/406mm at the diameter with a length of 23"/584mm. Solder or epoxy it to the open end of the coffee can.
Source: Popular Mechanics.
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