Half-Wave Center-Fed Dipole Antennas

Half-Wave Center-Fed Dipole Antennas

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The half-wave center-fed dipole is one of the most popular antennas in use today. In free space the center-fed half-wave antenna has an input impedance that is a close match to 50 ohm coax and to most radios that have a 50 ohm output impedance. (The actual impedance depends on the height of the antenna above ground and many other factors.)

The Frequency Devices half-wave antennas are built using #14 hard drawn 7/22 stranded wire (7 strands of #22 twisted together) to meet the National Electrical Code for antennas. Hard drawn wire is preferred in antennas because it will stretch less than soft drawn wire. Testing has shown that #14 bare 7/22 is a good, low resistance wire that radiates well.

This Antenna has been tested to withstand 100 pounds of strain over time without breaking. It can be installed as an inverted V or as a straight dipole. Our antennas are built using 18-8 stainless steel hardware, all internal nuts are self-locking, and all holes are sealed with RTV sealant.

The half-wave antenna has maximum gain off of both sides of the antenna (see Figure 1). Off of the ends of the antenna the gain is the lowest. This means that when you install the antenna you must point the two sides of the antenna in the directions you wish to communicate the most. This does not mean that the antenna will not work at all off the ends but the gain will be less.

Figure 1 shows the ideal free space radiation pattern of the half-wave dipole. This pattern will vary depending on how high you install the antenna, what kind of ground is located below the antenna, what buildings and structures are close to the antenna, etc.


Figure 1

We have two versions of the antenna, one with a Balun in the center section and one without the Balun.  For Half-Wave Center-Fed antennas with a Balun Look Here.  Each of these antennas is available for three different frequency ranges.  One of the problems with feeding and half-wave center-fed dipole directly with coax is that the dipole is a balanced device while coax is unbalanced.  A Balun should be used to convert the unbalanced coax to a balanced output to connect to the antenna.  Not using a Balun can affect the directional pattern of the antenna and can also result in having RF in your shack.  That said a lot of people have had a lot of success without one.  If you feel that you need one you can make one by coiling up 6 to 12 turns of coax on a 4 inch or 6 inch plastic form.  There are several books and articles available on this subject. 

We also have available some Dacron rope for hanging antennas. It is 1/8 inch, double-braided, black UV-inhibited top of the line rope. It will not stretch or break down under sunlight.