How to Design a Dipole Antenna
You can design your own dipole antenna for your favorite radio spectrum bands. Connect an antenna tuner between the antenna and your radio to fine tune its reception and transmission properties, and extend the antenna's frequency coverage without physically altering its length. Most dipole antennas for high frequency (HF) communications will be constructed out of wire; whereas, those for very high frequencies (VHF) or ultra high frequencies (UHF) are generally made out of aluminum tubing.
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Instructions
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Locate an area outside your home where you want to install your dipole antenna. You will need two supports for it. One can be your house, the other a tree, a pole or anything else that will support your antenna at least 20 feet or higher in the air.
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Look at a world map and decide in which two opposite directions from your location you want to receive from or transmit to. Although your dipole antenna will have some omni-directional capabilities, its maximum sensitivity will be at right angles to its axis. If you want to communicate primarily in an eastern or western direction, for instance, hang your dipole antenna in a north-south configuration.
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3
Decide what predominant frequency you want to work with, and design your antenna accordingly. Since dipole antennas work well on multiples of the predominant frequency for which they are designed, your coverage will extend to other frequency bands.
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For a half-wave dipole antenna, use the formula Length in feet = 468 divided by the frequency in megahertz (L=468/MHz). Add 12 inches to the calculated length for mounting and fine tuning purposes. During construction, the wire will be cut in half to be reconnected in the middle with an insulator to which a feedline (cable) to your radio will be connected.
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Decide which end and center insulators will be used. You can purchase them from ham radio supply stores or you can make them yourself from any sturdy insulating material.
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Measure the distance from the center point of your dipole antenna to your radio inside your home. This will be the length of the feedline that will connect the antenna to your radio.
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Tips & Warnings
If you design your dipole antenna for a primary frequency of 3.55 MHz on the 80 meter band, for example, it will also work on multiples of that frequency, including 7.100 MHz for 40 meter, 14.200 MHz for 20 meters and 21.300 MHz for 15 meters.
When you look for a location to hang your dipole antenna, be aware of any overhead high-tension wires that may come in contact with it. Consider the sway that they and your antenna may exhibit in high winds that could cause them to come in contact with each other.
References
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