Introduction: Easy to Build WIFI 2.4GHz Yagi Antenna
This antenna will extend the range of your WiFi or 2.4GHz devices (like surveillance cameras) into many miles and kilometers. A yagi antenna is basically a telescope for radio waves. I tired the pringle can antenna and the Yagi beats it hands down in performance.
Step 1: What You Need
This is an absolutely easy project.
You need an ink jet printer/ Computer
Big paper clips (you could use any stiff solid metal wire instead)
USB WIFI, preferably with an antenna extension OR a 2.4 GHz device
soldering iron and lead
Pliers or preferably a nibbler (see photo below, available at radio shack)
a metric ruler with millimeters or a metric caliper.
Step 2: Building Overview
The building steps are simple:
1. Print out the scaled Yagi antenna template* (download from next step).
2. Trim paper clips to size and glue them to the template.
3. Use Popsicle sticks to build the antenna's backbone and hold it together.
4. Connect the USB device to the antenna.
*I used a Yagi modeler java applet to generate the diagram. This modeler applet is found on many websites (google "yagi modeler") and its owner is W9CF.
The modeler gives a diagram and the elements' lengths and position. I carefully scaled the diagram and turned it into a template in order to make the building process easy.
You can visit AB9IL awesome website to get more details on using the modeler for this 15 element Yagi and other fine antenna projects, such as a 20 element WIFI Yagi .
Step 3: Printing the Yagi Diagram
The most essential point in printing the template is getting the correct scale. In the attached zip file below, are three png picture files.
The antenna is longer than an Letter sized or A4 sized paper. So you have to print the template in two parts (labeled part1 and part2 in the zip file). I have also included the full sized unsplit template if your printer can handle large enough paper.
Make sure to set your printer's properties to ORIGINAL SIZE (not "best fit to page" ect..).
Set the print orientation to LANDSCAPE.
Use a ruler or caliper to measure if the print is of correct scale. You will notice vertical bars crossing the horizontal line. The vertical bars represent the Yagi "elements" which will be made from paperclips. The horizontal line is the backbone of the antenna which will be build out of popsicle sticks.
You will also notice numbers next to the elements. These numbers are in pairs. The first number is the length of the element in millimeters. The second number, is the distance from the start of the diagram to the element, in millimeters.
Measure the size and position of a couple of elements on each prints. If your measurements match the numbers on the diagrams, then your print is to scale and you may proceed. Accuracy need not to be tight for the antenna to perform well.
Now superimpose both prints, until they match at around element 10 or 11, and tack them together with scotch tape or white glue.
Step 4: Cutting the Paper Clips and Fixing Them
You have to trim the paper clips with a nibbler or plier to fit the vertical bars ("elements"). This is fairly straight forward. Lay the paper clip on the template's element and mark the ends with a marker. Snip at the marking.
Make sure that each element fits correctly the length of the bar on the diagram.
Fix the elements in place with crazy glue.
Leave element #2 for later. This is the element that connects to the electronics and is called "the driven element" (as in being driven by electronics).
Step 5: Building the Backbone
The backbone holds the shape of the antenna. I just cut pieces of popsicle sticks and fit them between the gaps of the elements. I used white glue to fix them in place.
Start from element #15 backward. When you arrive to element #2 move on to the next step.
Step 6: Building the Driven Element
The "driven element" in a Yagi antenna, is usually the second one from the start. It is the element that connects to the USB WIFI or 2.4 GHZ electronics.
It is a broken loop and not a straight wire. A loop of wire resonates at a specific radio frequency depending on its dimensions. The dimensions of the driven element in this antenna is set at 2.4GHz, of course.
It just happens that its about the size of a common big paper clip. You need to clip the paperclip so that it loops around and meet in the center but the end not touching, leaving a gap (see photo).
Fix it in place with crazy glue and build the back bone around it.
When all the elements and sticks are in place, reinforce the antenna with another layer of popsicle sticks. Glue full lengthed popsicle sticks on top of the antenna. The antenna should become mechanically stiff. Then rip the paper template of the antenna.
Step 7: Connect the Antenna to the Wifi Modem
This is the most difficult part and depends on the electronic hardware you have. please read this step carefully.
The basic idea is that you need to solder a wire between the WiFi board's RF output and the driven element of the yagi antenna.
But USB WiFi modems come either with an internal antenna or with an external antenna. Those with external antennae, like mine, are easier to connect because you are just replacing the external whip antenna with the Yagi. Those with internal antenna may need to have their on-board strip antenna modified as illustrated in the pictures here. You need to slightly experiment in this case.
I have tried soldering a coax to my board's antenna connectors and the two ends of the yagi's active element loop but it did not work in my case. I have no explanations why that did not work, but other DIYers that have built Yagi antennae connected their antenna in this manner.
In my case, I just connected a single thin strand of copper wire between the active element of the strip antenna and one end of the loop of the driven element.
Please read the annotations of the pictures for more details.
Step 8: Performance
The performance was pretty spectacular for this easy to build antenna. I was able to see the WiFi of a hotel that was 2 miles away from my home. The most difficult part was connecting the antenna to the USB modem.
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