Use a Surplus Dish Dish as an IEEE 802.11 Wireless Networking Antenna

Use a Surplus Dish Dish as an IEEE 802.11 Wireless Networking Antenna

It is easy to make a satelite dish into a highly directional antenna for the very popular IEEE 802.11 wireless networking. The resulting antenna has about 22 db of gain, and is fed with 50 ohm coaxial cable. Usually LMR400 or 9913 low loss cable is used if the source is more than a few feet from the antenna. The range using two of these antennas with a line of sight path is around 10 miles at full bandwidth. I must stress the line of sight part though. Leaves really attenuate the signal.









Things You Will Need:
A Primestar dish. (You may use any old dish, but if it is bigger than the Primestar the gain will be higher, and it may not be within the Federal Communications Commission rules for use within Nigeria. In fact I have come to find out that there seem to be several different dishes that Primestar used, and I am only sure that the one I used, pictured above, used with the ordinary Wavelan or Airport transceiver card is within the effective radiated power limits given by the FCC.)
A juice can (about 4 inches in diameter and at least 8 inches long).
A chassis mount N connector.
You will also need a "pigtail" connector which has the proprietary Lucent connector (for the PCMCIA card) on one end and an N connector on the other. The pigtail can be obtained from a number of online stores for $35 to $40.
Construction Steps:
After deciding on a place to mount your antenna (which hopefully has a line of sight path to the access point or other IEEE 802.11 site), remove the apparatus at the feed position of the dish, saving the mounting hardware.
Using a can opener, cut one end of the juice can out, drink the juice and wash it out
Solder a quarter wavelength (1.15 inches) of wire onto the center conductor of the chassis mount N connector.
Using a punch or whatever other tools you deem necessary, mount the N connector so that it is about 1.2 inches from the closed end of the juice can as shown below. It is also a good idea to put a drip hole at the lowest point of the can to insure that water doesn't build up inside. After having this up a for a few months, I think it would be nice to put a plastic lid on the open end of the can so that the inside doesn't rust. During the time mine has been up, it has rusted and I have lost a couple of db on the signal strength. These two things may be correlated.
If you are certain of the polarization you will need, mount the juice can so that that polarization is achieved. (You want the antenna you are communicating with to be lined up with yours.) If you don't know the polarization you can set everything up and before mounting the juice can, experiment to get the maximum signal strength by rotating the juice can around its axis. Most commercial antennas I've seen are using vertical polarization, so that the picture below shows you the proper orientation. You want to mount the juice can so that the opening is just at the focus of the dish. In my installation I didn't quite achieve this, but I only lost a db or two by taking the easy route. I still have about 25 db signal to noise ratio, so this wasn't important to me. The easy route is to mount the can as far back as you can along the mount, by punching two holes through the can and bolting it in. The perfectionist's method would be to find the best feed place (which I found to be just a little farther back) and use some PVC tubing or something to extend the mount so the feed is in the perfect position. In some installations, every decibel will count and this should be considered.



The inside of the feed can.




Some Considerations:

This antenna is very directional. You must have it aligned very carefully, or you will lose a lot of signal. It also needs to be mounted securely, so the wind won't be able to rotate it even a few degrees.

This antenna is an offset fed dish, which means that the feed horn (our juice can) is not positioned as much in the way of an incoming signal, so it doesn't shadow the dish. This makes the aiming a bit tricky, because it actually looks like it is aimed down when it is aimed for the horizon. See the photo below of it aimed actually a few degrees above the horizon. You can use the scale on the dish mount to determine the elevation it is aimed at. The dish isn't as directional in the up/down directions as it is side to side. This is fortunate, because without turning the mounting upside down we can only get it set so it is a few degrees above the horizon. I sacrificed a db of gain here by not turning it over, mostly because I'm mounting it on a vent pipe, and didn't want to put that kind of wind load on it. As mentioned above I don't really need the extra signal either.




The mount of the dish. This photo also shows the angle it must be tipped to be aimed at the horizon.





I believe this feed system could be improved by linking two cans together (or using a section of pipe) to give the effect of lengthening the length of the circular wave guide feed. This would further attenuate undesired modes (other than the TE11 mode). The optimum length would be between 14 and 21 inches. The opening would still need to be at the focus of the dish.
Use the Feed Can By Itself

You can use the feed can by itself as a cheap antenna. It works as well as the commercially available "range extender" antenna, but only in one direction, and it is so easy to construct!
Some More Photos




A photo of the mounting of the feed can.








A photo of the coaxial connection to the feed can.
IEEE 802.11a
This antenna modification is for the IEEE 802.11b networking protocol that operates at 2.4 GHz. It can be scaled easily to the 5 GHz frequency used by IEEE 802.11a by simply scaling the dimensions on the feed can and the excitation antenna to 2.4/5 = 48% of the dimensions shown above.

How To Build A Tin Can Waveguide WiFi Antenna

How To Build A Tin Can Waveguide WiFi Antenna
for 802.11(b or g) Wireless Networks
or other 2.4GHz Applications


Got no dough for a commercial WiFi antenna? Looking for an inexpensive way to increase the range of your wireless network? A tin can waveguide antenna, or Cantenna, may be just the ticket. This design can be built for under $5 U.S. and reuses a food, juice, or other tin can.
I am not an electrical engineer, nor do I have access to any fancy test equipment. I've built some antennas that worked for me and thought I would share what I learned. I have no idea if this is safe for your radio or wireless network equipment. The risk to you and your equipment is yours.





Building your Cantenna is easy, just follow these steps.

Collect the parts
Drill or punch holes in your can to mount the probe
Assemble the probe and mount in can


Collect the parts:
You'll need:

A N-Female chassis mount connector.
Four small nuts and bolts
A bit of thick wire
A can
These vendors can supply the parts (the wire and can you provide yourself).

The Connector
A N type Female Chassis-mount connector. One side is N-female for connecting the cable from your wireless equipment, and the other side has a small brass stub for soldering on wire. These can be found at electronics stores internet suppliers (see the list below under "Connect your antenna..." If you shop around, you should be able to find these for $3-$5.

Nuts & Bolts
You'll need them just long enough to go through the connector and the can. I've used #6x1/4" stainless. If your N-connector is a screw on type, then you won't need the nuts and bolts.

Wire
You'll need about 1.25" of 12 guage copper wire. This wire will stick into the brass stub in the N-connector.




Drill or punch holes in your can to mount the probe
The N-connector assembly will mount in the side of your can. You need to put holes in the right place to mount the connector. The placement of the hole and connect is very important. It's location is derived from formulas that use the frequency that the antenna will operate at and the can diameter. To make life easy on you, here's a calculator to figure it out for you.



Enter the diameter of your can above and click on the calculate button. 802.11b and 802.11g WiFi networking equipment operates at a range of frequencies from 2.412 GHz to 2.462 GHz. Ideally, with your can size, the TE11 cut-off frequency should be lower than 2.412 and the TM01 cut-off should be higher than 2.462. It would be good, also, if your can is longer than the 3/4 Guide Wavelength. If your can is a little off in length or diameter, don't despair, experimentation is fun!

You want to mark the location on the can where you will put the hole for the connector. The 1/4 Guide Wavelength number tells you how far up from the bottom metal end of the can to put the center of the hole. Open only one end of your can, eat the contents, and give it a good washing. You'll probably want to remove the label too. Use a ruler to measure up from the closed end 1/4 Guide Wavelength and mark the can with a dot.

If you've got a drill, select a bit that matches the size of the center of your connector. You may want to start with a small bit and work the hole larger and larger. You could even start with a hammer and nail, then use drill bits. If you don't have a drill, start with a nail hole and use a file to get the hole to the required size. If you're using a bolt on connector, make four more holes for the bolts - you can use the connector as a drilling guide.


Click on image to enlarge
Assemble the probe and mount in can
Now you'll need that bit of wire. You'll need a soldering iron or a friend with one as well. Cut the wire so that when it is stuck in the connector as shown, the total length of both the brass tube and wire sticking out past the connector is 1.21". Get as close to this length as you can.

When you've got your wire correctly sized, solder it into the connector keeping it as straight and upright as you can. When it's cooled, bolt or screw the assembly into your can. Put the heads of the bolts inside the can and the nuts on the outside to minimize the obstructions in your antenna. Your Done!




Connect your antenna to your wireless card or access point
To use your cantenna, you'll need a special cable commonly called a "Pig Tail". The pig tail connects your wireless card or access point to you antenna. One end of the cable will have a "N" Male connector (just right for connecting your your cantenna), while the other end will have a connector appropriate to your card or access point. For a good picture of a pig tail, take a look at:
http://www.seattlewireless.net/index.cgi?PigTail

You'll want to have a wireless NIC or access point with an external antenna connector. Otherwise, you may have to hack into the one you have to hook up the cable. I wouldn't recommend this unless you're good with a soldering iron and electronics. For this reason, I like the Agere Orinoco cards which have a nice antenna connector. Pig Tails can be hand made if you have the right tools, but it's probably easier to get a pre-made one. Try:

Fleeman Anderson & Bird
Fleeman Anderson & Bird has a "cantenna kit" for sale that includes the connector and pigtail. Choose one of the "cables" links from the menu and look towards the bottom of the list.
Hyperlinktech
Antenna Systems
Hook up your cable, point the antenna at a friend's, and see how far you can stretch you network. Be sure to let me know (greg@turnpoint.net) how it works.

This antenna has linear polarization. That means that how you rotate the antenna will affect the strength of your signal. Usually, you will want to put the connection straight down, but experiment with rotating the can while watching the signal strength on your PC to get the best performance.









http://www.turnpoint.net/wireless/cantennahowto.html