Wire Antenna: Difference between revisions
(Added more text. Ultimately I think the content of this section doesn't belong under "Wire", since it applies to all antennas. We should think about moving it.) |
(Cleaned up text. Removed references to impedance mismatching, which is too complex for a general article and not limited to wire antennas. We need to move that to a separate detail article.) |
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Many amateur radio antenna systems use a simple wire to carry the RF current in such a way as to radiate. One of the simplest is the half-wave center-fed [[dipole]]. When a | Many amateur radio antenna systems use a simple wire to carry the RF current in such a way as to radiate. One of the simplest is the half-wave center-fed [[dipole]] with [[coax]] feedline. When a radio-frequency oscillating current is applied to a dipole, the [[magnetic field]] generated around the wire expands and contracts very quickly, in most cases millions of times per second. It is the outer most part on the field that is radiated away. | ||
The shape of a [[dipole]] resembles the letter "T". The middle leg connects the radio to the center of the upper, horizontal legs. There are several ways to make the connection. The simplest has the coax shield connected to one side and the center conductor connected to the other side. | The shape of a [[dipole]] resembles the letter "T". The middle leg, which consists of the [[coax]] feedline, connects the radio to the center of the upper, horizontal legs. There are several ways to make the connection. The simplest has the coax shield connected to one side and the center conductor connected to the other side. However, this can cause [[feedline radiation]] due to [[common-mode currents]]. It is often recommended that a [[balun]] be attached at the feedpoint, but many operators have good success with dipoles that have no baluns. | ||
The feedpoint impedance of a horizontal [[dipole]] various dramatically depending on the electrical height above ground. | The feedpoint impedance of a horizontal [[dipole]] various dramatically depending on the electrical height above ground. | ||
Refer to the article on [[impedance matching]] for more details on connecting transceivers to [[feedline]] and [[feedline]] to antennas. | Refer to the article on [[impedance matching]] for more details on connecting transceivers to [[feedline]] and [[feedline]] to antennas. | ||
Revision as of 18:15, 20 May 2008
Many amateur radio antenna systems use a simple wire to carry the RF current in such a way as to radiate. One of the simplest is the half-wave center-fed dipole with coax feedline. When a radio-frequency oscillating current is applied to a dipole, the magnetic field generated around the wire expands and contracts very quickly, in most cases millions of times per second. It is the outer most part on the field that is radiated away.
The shape of a dipole resembles the letter "T". The middle leg, which consists of the coax feedline, connects the radio to the center of the upper, horizontal legs. There are several ways to make the connection. The simplest has the coax shield connected to one side and the center conductor connected to the other side. However, this can cause feedline radiation due to common-mode currents. It is often recommended that a balun be attached at the feedpoint, but many operators have good success with dipoles that have no baluns.
The feedpoint impedance of a horizontal dipole various dramatically depending on the electrical height above ground.
Refer to the article on impedance matching for more details on connecting transceivers to feedline and feedline to antennas.