Long Range Gain WiFi Antenna
I must fault my sister who sent me a link to a really neat project of a home constructed Long Range Gain type WiFi antenna made from easily obtained parts right on your pantry shelf. The source document that was sent to me may be found here http://blog.jgc.org/2012/02/long-range-wifi-antenna-from-illy.html This blog is maintained by John Graham-Cumming.
However the readily available can size was not found in my pantry and so I was left with the burning question of what can I use in place of the 3.25 Inch in diameter can.
On a trip to my local hardware store where I was actually buying something entirely different I spotted this neat device that is used to provide an interface between an exhaust fan through the wall of a structure finally day lighting outdoors. Such devices are used with home dryers or various exhaust fans. Lo and behold this device consisted of a 3 inch in diameter aluminum cylinder that was 12 inches long and was fitted to a plastic cover plate that installs on the outside of the structure. The unit is manufactured by Lambro Industries Model # 222WS
Well it took about a nanosecond to reach into my wallet to find $6 plus tax and that baby was mine. Next I thought about how to enclose the end of the tube and how to come up with a perhaps better approach to installing an N -Type connector.
The end closing was actually pretty simple. I took a square piece of thin Tin stock I happened to have but the same material in aluminum works too. I started with a piece 4 X 4 inches square and using the old method of drawing pencil lines from opposite corners the intersection of the two lines is the middle of the stock. (I actually was listening when I took geometry in the 7th grade.) Next using a compass and at the center point I drew a circle that was three inches in diameter. I then proceeded to draw a circle 4 inches in diameter which is actually tangent to the four edges at the mid-point of the 4 inch sides.
Using a pair of tin snips I cut away the excess material from the 4 inch circle. The next part is best done after having at least one beer as it can get tedious. Starting at the outer circle and at 1/4 inch intervals, with the tin snips, make a cut from the outside circle right to the edge of the 3 inch circle. Go all the way around the circle. Some math -- a 4 inch in diameter circle means that the circumference is 4 X Pi = 12.57 inches. Since there are 4 cuts to the inch you will have to make about 50 cuts --make that two beers. Once that is done then taking a pair of needle nose pliers bend up each small sector using care to make the bend line right at the edge of the 3 inch circle. As a mater of fact if you bend each sector slightly inward when the cap is in place on the end of the tube, the sectors act like fingerstock and give a really snug fit. When I was done I wrapped about three turns of electrical tape around the the circumference of the tube which applies a little pressure to the finger stock and prevents water intrusion and keeps the electrical contact "solid".
I wanted something easier that trying to install an N -type connector on a thin aluminum tube. That is when I decided to use SMA type connectors, which only required the drilling of a 1/4 inch hole for the antenna penetration and using a two hole bulkhead style connector only required drilling two small mounting holes to accommodate a 2-56 nut and bolt. Using the length calculator in the article, the antenna 1/4 wave length for a 3 inch diameter tube is 3.74 inches. I eyeballed something slightly less than 3 and 3/4 inches. For the antenna I took a piece of #16 heavy enamel coated copper wire and filed down the end so it would fit into the solder pocket on the SMA connector. I started with a piece 1.5 inches long. The finished length installed in the connector measured from the bottom of the connector to the top of the wire is supposed to be 1.21 inches. After soldering I measured 1.25 inches and then did some eyeball pruning to get it as close as I could to what I thought should be 1.21 inches.
Next I paid attention to the effects of attenuation as mentioned in the blog. So with the SMA connector installed on the tube I purchased a pre-made 1 foot long cable 50-Ohm cable with a male SMA mating connector on each end. However to attach to the WiFi electronics which ultimately connect to your computer via a USB cable requires an in-series adapter as the WiFi part has a male jack type connector too. So the adapter has a female jack and female plug at either end. It is available from Mouser P/N 565-72967, or from Pomona Electronics P/N 72967. That jewel costs about $13. Again the goal was to maximize the signal from the antenna to the WiFi unit and if a longer cable was needed it should be on the USB side.
Does it work? Yes! My crude test was to point the antenna away from my wireless router access point and observe the number of bars on the laptop. I then pointed the antenna at the wireless router and full bars and excellent signal strength. I even spotted an open "apple" router in my neighborhood --never saw that before.
The total cost including the WiFi electronics was about $50. Oh should mention that the plastic housing is ideal for mounting the antenna to some structure or perhaps a tri-pod.
Have fun homebrewing --- Pete N6QW -- email email@example.com