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How to Run Open Copper Wire to a CB Antenna

Coaxial cable with a characteristic impedance of 50 ohms, such as RG-8 or RG-58, is the most common antenna feedline used to connect a CB antenna. But CB, or Citizens' Band, is within the high-frequency portion of the radio spectrum, and like other HF bands, it also works well with a simple open-wire feedline made of copper wire.

Open-wire feedlines have a high characteristic impedance of 300 to 600 ohms, so the radio hobbyist typically uses an RF transformer to step down the impedance. There is a simpler way, though. Because a half-wavelength line repeats the impedance it encounters at the end, the open-wire feedline that is an exact multiple of a half-wave will effectively be the same low impedance as the antenna feedpoint.

Things You'll Need

Copper wire
Wire cutters
"Dog-bone" antenna insulators
Nylon twine

Instructions

- 1
  Decide where you want the antenna and the radio. Find a path for the feedline to run between the antenna and radio. Avoid any metal objects.
- 2
  Measure the distance of the feedline path. Calculate how many half-waves will fit in the space, and adjust the position of the antenna and/or the radio to arrive at an exact multiple of half-waves.
  
  The formula for a half wavelength is 468 divided by frequency in Megahertz. CB is 27 MHz, so 468 divided by 27 is 17.33 feet. You also need to account for the velocity factor of the line, which is approximately 85 percent; so the actual length of a half-wavelength of line is 14.73 feet.
  
  As an example, if you wanted to place the antenna 50 feet from the radio, 5 divided by 14.73 is 3.39 so you would need to either cut the line to 58.92 feet (4 half-waves) and move the antenna farther out, or cut the line to 44.19 feet (3 half-waves) and move the antenna closer.
- 3
  Cut two sections of wire to the exact length you calculated in Step 2. Slide the dog-bone insulators over the two wires and tie them in place with the twine so they keep the two wires separated. Space the insulators approximately 12 to 14 inches apart.
- 4
  Connect one wire to each half of the antenna, if a dipole or other balanced antenna. Connect one wire to the radiator and the other to the ground plane, if an unbalanced antenna such as a quarter wave.
  
  At the radio end, connect one wire to the center conductor of the antenna connector. Connect the other wire to the outside of the antenna connector, or to any convenient chassis ground on the radio.

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