Parabolic Wi-Fi Dish

Make a parabolic Wi-Fi dish to boost your Wi-Fi reception from junk laying around your house. This simple project was not intended to be a masterpiece of mechanical engineering. It is simply my idea of how to make your Wi-Fi signal a little better hopefully without spending much cash.

The way a Parabolic works is that it reflects the signal from a larger surface area than that of the antenna alone. Then concentrates it at the focal point. This dish as crude as it may look gives me ~13db gain receiving from the same router it was before. Don't confuse this as a booster it has no power so it is not amplifying the signal it is only concentrating it. Thank goes to rimar2000 for pointing out my lack of description.

This thing isn't all that good looking but if you consider that I am getting a signal from my brothers house over 300 yards from my apartment threw 2 walls made of dry wall. ! brick wall. Across a major road. Threw his brick wall to his router.

Without the dish I was getting a signal quality of 4-7% signal 1Mbps link and constant drop outs.

Now I get
link Speed 18Mbps
Signal -79
Noise -90
SNR 11
Signal Quality 19%
www.Speedtest.net    Test Download 7Mbps Upload 1.5Mbps

You are going to need:

1/4" Threaded rod
Electrical or Duct Tape
Cardboard
Aluminum foil
Some kind of adhesive like spray glue, rubber cement, or elmers Glue
A few old CDs
And anything else I forget to list!!

Step 1: Calculations
The first thing you are going to want to do is understand somewhat how a parabolic dish works. You can do a bunch of Googleing and reading and still not understand the mathematics behind wave angle, Illumination angles, etc. Lucky for the not so math savvy some people smatter then me have done all the hard work in a multitude or simple programs. I have chosen “Parabola Calculator 2.0” found here http://mscir.tripod.com/parabola/.

For my dish I have decided to go with 68cm diameter and a depth of 18cm. (That’s about 27inch diameter 6.25inch deep). I recommend you use metric (CM) to do all your measuring as it is easy to figure the lengths with the program. Naturally in this case the bigger the better. A larger dish will collect more of a signal. So if you feel frogy go right on ahead and make yours 6 foot.

Input your Diameter and Depth into Parabola Calculator and hit calculate. It will draw (with default setting) a dish in blue and the focal length in red. Notice that when to hover your mouse over the black area you get a cross and some numbers X and Y will appear at the bottom of the window. The numbers indicate the distance from the deepest part of the dish (center) out to the edge (X) and how deep they are (Y).

Step 2: Layout
Taking the calculations from Step 1 you will want to lay out the curve of the dish on a flat surface. Accuracy is important but you can be off slightly and still have an operational dish.

First measure your width (diameter) and find the center point. Now go to Parabola note a point (X, Y) on one side of the dish. Then measure the bottom edge from the center out to one side. Then measure the height up from that point. To assure you are not off to an angle use a T square if you do not have a T Square you can measure the depth again from the center of the dish Up and then from there the distance to the side. Repeat this process on the opposite side. Then do it again 3-4 more times at different points on each side marking each point with a dot or X. Connect the dots and you should end up with a curve like the one in Parabola.

Step 3: Bending Supports and forming the dish base

Now that you have your template made. Use something that is rigid but bendable to make 4 rods. I used some ¼ inch threaded rod I had laying around from another project.

Find the Center of the rod and chop it in half. I recommend bending the rod 1st because bending and forming a longer rod is easier than a short one.

Then use an octagon shaped piece of wood and drill holes in the side at the 12, 1:30, 3, 4:30, 6, 7:30, 9, and 10:30 positions. Drill holes in the side of the octagon about 2 inches deep. If you are using wood and a 7/32 inch bit the threaded rod should tap itself in. If not then use a 1/4inch bit to ream out about ½ the hole and it should tap in after that. Add some Super Glue and a little electrical tape to shore it up. Be sure to check your curves again just in case you bent it up a little.

Step 4: Feed horn and back Reflector
Now we are going to work on the feed horn. This is the part the sticks straight out of the center of the dish that your USB device or router antenna will be fitted on. Once the signal is reflected by the dish it will concentrate @ a point called the focal. This is the spot in the dish that will have the strongest concentration of signal. At this point you could just it mount up and be done with this step. Personally I like to get all I can so I am going to make a 2nd mini dish to reflect any signal loss due to miss adjustment or placement of the receiver.

CAUTION HOT STUFF BURNS!!!! Preheat the oven to 375 and place a CD on top of a curved lid or glass condiment dish. Place them in the oven. It should only take a few minutes to soften the plastic. Over cooking it could badly deform it so it’s better to go short on time and start over if it’s not hot enough to bend. You are shooting for a circle about 10cm (4 inches) round and 2-3cm deep.

Take note CDs are made to take some heat and not bend. One thing I notice is that a CD will tend to curl upwards rather than down when it’s almost to the state it will form. Bending it too far will cause breakage or deformation. I use a pot holder to apply pressure on the CD after removing it from the over and placing it on my glass condiment bowel. CDs are cheap so wasting a few while you get it right is ok. If you want a more workable plastic get a small piece of Lexan from a hardware or home improvement store.

Now Take the diameter and depth of the mini dish and plug it into Parabola. Take note of the focal length.

Add the Focal Length of the main dish and the mini dish. This is how long the center of the deepest part of the main dish and the deepest part of the mini dish has to be. Drill a hole in the mini dish and the wood center of your main dish. Install a rod passing it threw the mini dish and all the way thru the center ring of your main dish. Allow it to go all the way thru the main dish wood center so that it can be adjusted if needed. If you look the picture you will notice I did not go directly in the center. I drilled the hole ½ inch lower than the center on both dishes to allow room to mount the antenna or USB stick and still allow it to be in the center plane itself.

Now tape, glue, or screw on another rod to have something to use for a handle or mounting.

Step 5: Skinning it up

Now here you have a few options. You could use Aluminum but the cost would run you over an already made dish. Another option is Aluminum cans. For mine I am going to skin it by cutting eight cardboard triangles and cover it with aluminum foil and spray glue. Use some electrical tape to hold it all together. You could also use duct tape, aluminum tape, flashing or just about anything the is metal and reflective .