Hobbies And Interests
Things You'll Need
Instructions
Decide for what primary frequency you are going to design your HF dipole antenna. Since it will also work on multiples of the primary frequency, your dipole antenna will function on different bands as well.
Use the formula L = 468/MHz to calculate your dipole antenna's length. L is the length of the entire antenna in feet and MHz is the primary frequency in megahertz that you want your antenna to be most efficient on. For example, if your primary frequency is 7.150 MHz in the 40 meter band, the length of the antenna will be calculated as 65.5 feet.
Add 12 inches to the calculated length of the wire. You will use some of the extra length to trim the antenna for fine tuning, plus you will use the rest to tie the wire to the end insulators for installation support. Cut the wire into two equal halves.
Connect each one of the two wire halves to the middle insulator. Solder one feedline conductor to one of the antenna's wires and solder the other feedline conductor to the other antenna wire. If the feedline is coax cable, for example, then one conductor will be the coax's center wire and the other conductor will be its outer braided shield.
Decide on a location for your dipole antenna. You will need two supports that will hold the antenna at least 20 feet in the air. If you have limited space, erect your dipole antenna in one of the different space conservation configurations such as the "Inverted-V," the "Inverted-L" or the "Sloper" which only requires one support.
You will fine tune your antenna if you are not going to use an antenna tuner. Loosely connect both ends of your antenna to the end insulators and hoist the antenna into the air with nylon rope that has been attached to the end insulators. Use low power on your transmitter and check the antenna's efficiency with a watt or a standing wave ratio (SWR) meter. Carefully trim small, equal pieces off each end of the antenna after lowering it, and retransmit on low power to test the antenna. Continue to trim the wire ends until the meter readings indicate peak efficiency.
If you are going to use an antenna tuner, tie both antenna wires securely to the end insulators and hoist everything onto the antenna supports. You will adjust the electrical length of your dipole antenna with your antenna tuner for maximum efficiency.