Inexpensive Homebrew Airband Biconical Antenna
I was looking for a commercial scanning antenna, but they were all to big for my apartment porch and the cost! So I decided to try a homebrew. After some study I came to the conclusion that a biconical antenna was the answer. It would be resonant on the frequency I wanted and could be easily put up and taken down when needed. I even had all the parts needed so it would be cost free.
I was going to use it on a dedicated scanner on the Guard Channel 121.500, but I also use it to pick up ACARS tranmissions with great results. I have no problem picking up flights hundreds of miles away and low on the horizon. To make it as compact as possible I decided to build a Quarter Wavelength Antenna. Calculating the radials I came up with 23.11 inches. This will make it possible to build a antenna less than 32 inches tall.
8 - 23 and 1/8 inches of stiff wire (wire coat hangers work well)
1 - 32 inch dowel rod or PVC pipe
1 - 12 inch piece of stranded wire insulation removed
1 - 12 inch piece of antenna coax
1 - correct adapter to fit your antenna feedline
Measure all 8 pieces of stiff wire (radials) to the same 23 and 1/8 inches. Now measure 7 and 3/4 inches from the end of each radial and bend into a "L" shape. Grab the dowel rod/Pvc Pipe and place a mark at one inch from each end. Drill a hole alittle larger than the radial diameter. Turn the dowel rod 90 degrees and repeat until you have 4 holes. Go to the other end of the dowel rod and repeat. Keep the holes at the top and bottom lined up. Now measure from each of these 8 holes 13 inches toward the center of the dowel rod and drill 8 more holes again keeping all the holes inline. Once done it is time to insert the radials. Place a dab of glue into the holes as you work on them. The short 7 and 3/4 inch side of the radials are placed in the holes closet to the ends. While the long sides will need to be bent further in to reach the center holes. You also have to make a small bend at the ends so the radials can be easily inserted into the center holes. Let the glue set. Check to make sure the radials are firmly set. Now to electrically connect the lowers radials together and upper together. DO NOT ELECTRICALLY CONNECT THE UPPER AND LOWER RADIALS TOGETHER. To do this take your standed wire and wrap it around one lower radial go to the next wrap again and continue until all 4 radials are electrically connected. Repeat with the upper radials. Solder the stranded wires to each radial. Now strip the coax cable and solder the center wire to one of the upper radials and the outer coax wire to one of the lower radials. Zip tie the coax to the dowel rod so that the wind doesn't loosen the coax solder connections. Attach the appropriate coax adapter and your ready to go. Since I live in a apartment I use a screw hook in the top of the dowel rod so it can hang on my porch. You'll need to figure the best way to erect your antenna for your needs.
Last edited by Wulfbane; 2010-07-27 at 03:28.
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