How to Build a VHF Dipole Antenna

Ham radio is an exciting hobby. One of the bands that ham operators use is VHF (Very High Frequency), from 30 to 300 megahertz. A simple dipole antenna made with basic copper wire and insulators can get you on the air quickly. It is important to remember that while you are free to listen anytime, you must have a license from the FCC to transmit on these frequencies.

Difficulty:

Moderate

Instructions

Things You'll Need

• Calculator
• Pencil
• Paper
• Measuring tape
• Roll of 18 gauge copper wire, 20 feet
• Wire cutters
• 2 ceramic insulators
• 2 wooden posts, 10 feet long
• Post hole diggers
• 1:1 balun
• Screwdriver
• Roll of 1/4-inch rope, 50 feet
• Roll of 50 Ohm coaxial cable, 50 feet

1. Determine the center frequency you will trim the antenna for and use the fixed formula below to calculate the length of wire needed.

   Formula: Length of wire = 468/frequency
   Example: Length of wire = 468/152.000 Mhz
   Length of wire = 3.08 feet, rounded up to 4 feet.

   The total length of the antenna will be 4 feet with each leg of the dipole being 2 feet long.

2. Measure and cut a length of copper wire to 4 feet, 4 inches (4 inches are added to allow for extra to be wrapped through each insulator). Cut this wire directly in the center so each leg is 2 feet, 2 inches long.

3. Insert 2 inches of one end of each piece of wire through a hole in each insulator and twist it around the insulator to hold it in place. Measure and cut two pieces of rope that measure 3 feet each. Tie one end of each rope through the remaining hole in each insulator so that each insulator has the copper wire on one end and the rope on the other.

4. Find an area for the posts to be placed in the ground. Dig a post hole 2 feet deep, place one post in the hole and bury the end with dirt to hold it in place. Measure 10 feet away from this post and dig a second hole, securing the other post there.

5. Attach the two free ends of the copper wire to the balun. Attach one wire to the screw on one side and the remaining wire to the screw on the opposite side. Tighten the screws with the screwdriver.

6. Screw the male connector on one end of the coaxial cable into the female connector on the bottom of the 1:1 balun.

7. Tie the free end of one of the ropes to the top of one of the posts. Stretch the antenna out and tie the other rope to the remaining post.

8. Run the remaining end of the coaxial cable to the radio, and screw the connector on the cable onto the female connector on the rear of the radio.

9. Turn the radio on and test for operation.

Tips & Warnings

• Never assemble an antenna so that it is close to any power lines, as contact with them could cause serious injuries.

• Transmitting on any amateur radio frequency without a legal license from the FCC is a violation of federal law.

• Be sure that your radio is grounded to avoid any RF or electrical surges through the cable from the antenna. Follow the manufacturer's guidelines for how to ground your particular model radio.

References

• BuxComm Corporation: The HAM Radio Operator's Antenna Handbook
• Command Line: Radio Frequency Chart

Resources

• Electronics Tutorials: Antenna Basics