How to Make a Yagi UHF Antenna

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Shintaro Uda and Hidetsugu Yagi created the Yagi-Uda antenna, better known as the Yagi antenna or Yagi, in 1926. Yagi antennas tend to be used by novice radio operators for communication on short-wavelength frequencies transferred through VHF/UHF microwave bands. Novice radio operators often "homebrew" this sort of antenna. The antenna is categorized into three fundamental parts: reflector, driven element and directors.

Things You'll Need

  • Ruler and pencil
  • Carpenter Knife
  • Drill and drill bits
  • Small metal file
  • Soldering iron and solder
  • One-inch paintbrush
  • Clamp
  • Resin adhesive
  • Cable ties
  • 50-inch coax cable with connector
  • 3 mm diameter brass rod 33 1/2 inches long
  • 1-by-2-by-15 strip of wood (2)
  • Cut the 3-millimeter diameter brass rod into seven pieces. You can purchase this type of item at any of your local hardware stores. You will need to cut the rod precisely for the following three sections: reflector, driven elements and directors. One cut piece will make up the "reflector" and it needs to measure 171 mm of an inch. Two pieces will become the "driven elements" and they must measure 74.5 mm. Four pieces of the brass rod will be the "directors," and those lengths need to be 132 mm, 128 mm, 120 mm and 115 mm.

  • Position two wood pieces, purchased from a lumber or hardware store, together on an industrial strength worktable. The wood pieces should measure 1-by-2-by-15 3/4 inches. When placing them onto the table, they should be arranged in a rectangle shape measuring 4-by-15 3/4 inches. Take a pencil and mark off these measurements at specific points on the wood, 22, 74, 135, 199, 237 and 277 mm. You want to utilize a t-square tool to help you in this process. Place the t-square tool flat against the wood and begin to draw a thick line across the wood at each designated mark. By doing this, you will know where to place the metal rods.

  • Make a 1.5mm-deep groove along each marked line on both pieces of wood. When cutting the wood, make sure you remove enough of the wood so the rod fits securely. Check to see if the cut grooves you made are deep enough by placing a single rod in the grooves, and then laying on top a second wood piece. The two pieces of wood lying flat should hold the rod in place.

  • Using a drill, generate a hole in the middle of the groove. You want the hole to be 237mm within one of the wood pieces. The hole needs to be large enough to allow the coax cable to pass through. Make sure you center the hole where the driven elements stick out from either direction of the wood fixtures.

  • Push the coax cable through the hole, allowing it to come out within the groove(s). You want to ensure that there is enough wire to allow for movement and flexibility. With a carpet knife, trim 15 mm of insulation covering from the end of the coax cable. Undo the braided metal and begin twisting it together between your fingers and hands. Softly bend the copper wire to one side, making a small "T shape" formation. It might be necessary for you to scrape away metal foil from the wire and remove approximately 12 mm of Teflon.

  • Organize the two driven element pieces for soldering. Flatten approximately a 5 mm section at the ends of each of the two 74.5 mm long rods. With the aid of a metal file, remove half the width of the rod to where there is a single curved section on the bottom. Remove the sod and twisted wire from the cable end, allowing it to fit within the flattened area of rod. Secure by soldering one twisted braid-end to a single drive element, and then solder the second.

  • Make a modest amount of liquid plastic resin adhesive. Paint a coating of liquid plastic resin on top of the grooves from the piece of wood with the cable inside it. Pull the cable to assist in positioning the drive elements inside the groove without breaking the connection. Press the rods straight into the groove ensuring that both sides never contact the other. Position the smallest of the directors within the first groove at 20 mm and press straight down. Put the remaining three directors into their grooves. Do this by overall size from smallest to biggest. Position the lengthiest of the reflector rods into the last groove.

  • Paint a narrow coating of liquid plastic resin on the top surface area that holds the rods inside. Modify the rods to center all of them on the antenna. Paint the grooves and flat surface section of the second wood piece, then carefully place the wood over the rods. Ensure that it is in line with the sides of each piece of wood. Use a clamp to hold tight the wood, until secured in place.

  • Get rid of the clamp and secure the coax cable onto the wood by utilizing cable ties to guarantee the cable doesn't move and weaken the contacts. Install the antenna exactly where you would like to use it and connect to your system.

References

  • Photo Credit antenna 2 image by Madrider from Fotolia.com
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