KA5WNX Antenna Workshop
The Dipole Antenna
The Half Wave Antenna....
The half wave dipole antenna is the simplest antenna to make. It is comprised of two quarter length wavelength elements with a insulator separating them by about 1/2" to 1" in total.
Each leg is 1/4 of one wavelength long. The feed point will provide approximately 72 ohms at the feed point.
The formula for each leg of the dipole is as follows:
234/frequency in MHz.
At 7.2 MHz it would be....
234/7.2 = 32.5 feet, or 32 feet and 6 inches.
The total length of the antenna would then be 65 feet in length.
The total length formula is 468/frequency in MHz.
Each leg is 1/4 of one wavelength long. The feed point will provide approximately 72 ohms at the feed point.
The formula for each leg of the dipole is as follows:
234/frequency in MHz.
At 7.2 MHz it would be....
234/7.2 = 32.5 feet, or 32 feet and 6 inches.
The total length of the antenna would then be 65 feet in length.
The total length formula is 468/frequency in MHz.
The Dipole
The basic dipole antenna is of the simplest design, yet most used antenna in the world. The dipole claims a gain of 2.14dbi over isotropic source. The center conductor goes to one leg of the dipole and the outer conductor (braided wire) goes to the other.
The dipole antenna impedance ranges from 36 ohms to 72 ohms depending upon the transmission line used, with 52 ohms as the norm using RG-8 or RG-58. Open wire will be 72 ohms.
Seperation of the center and outer conductor where the coax or other feedline connect should not extend beyond 1" inch. Always mount the dipole at least it's total length, or greater height above the ground or building for best results.
The dipole antenna impedance ranges from 36 ohms to 72 ohms depending upon the transmission line used, with 52 ohms as the norm using RG-8 or RG-58. Open wire will be 72 ohms.
Seperation of the center and outer conductor where the coax or other feedline connect should not extend beyond 1" inch. Always mount the dipole at least it's total length, or greater height above the ground or building for best results.
Example of FM Radio Antenna
Low End FM: 88 Mhz:
234/88 MHz = 2 feet and 8 inches per leg, total length 468/88 = 5 feet and 4 inches.
234/88 MHz = 2 feet and 8 inches per leg, total length 468/88 = 5 feet and 4 inches.
