Monoband HF Dipoles - Tips and Hints for Construction and Use

Half-wave Dipoles and Inverted Vees are very easy to construct, and are great for homebrew projects. You may purchase commercially made dipoles or a kit with end insulators and center insulators with coax connectors built in; or, make it homebrew from scratch and make your own hardware and purchase the wire.  If you are going to use a balun at the feedpoint, depending on how much home brewing you want to do, you can purchase a balun to use with the other materials you have gathered or perhaps take a shorter route and purchase a center insulator with the balun built in.

The antenna  is called a half-wave antenna because its length corresponds to an electrical half wave at the frequency for which it is cut.  The formula to calculate the (approximate) overall physical length of a dipole is:

Shown below are typical installation configurations, i.e. as a Flat Top supported by trees or structures of some type at each end, or, as an Inverted VEE requiring a center attach point and lower attach points at the ends.   

The calculated length of wire given by the formula above is cut in half to make both sides of the dipole equal.  Thus, this is called a balanced antenna because it is fed at its exact center. The above formula gives an approximate result because the length at the desired resonant frequency is affected by its operating environment conditions.  It is recommended to cut your dipole wire 2-3% longer than the length given by the formula·         

You can feed your dipole with coax.  Acceptable feedline can be 50 O coax, such as RG-58, RG-8X, RG-8, RG-213, or 75 O types such as RG-11, RG-59.  The coax should be sized to the power handling capability you intend to operate.
 A balun is not absolutely required, but a good idea. Coaxial cable is unbalanced. When feeding a balanced load, such as a dipole, with an unbalanced transmission line, the antenna will induce RF currents on the outer shield of the coax.  There are a number of fine “current” type baluns commercially available.  For the advanced and determined, builder one can also homebrew his own and info on baluns is readily available.  

When feeding the single band dipole with an unbalanced feedline (Coax), the use of a current balun will force equal currents into the unbalanced legs of the dipole.  Thus, typical properties and radiation patterns are more predictable.

Maximum radiation is at right angles to the antenna wire. This pattern in free space is with the dipole running North/South, thusmaximum radiation is equally East and West.