2013年1月6日星期日

Types of Two Way Radio Antennas

Dipole Antenna
The most basic type of radio antenna is called the “dipole.” A dipole antenna is made essentially from one single wire oriented horizontally, with a connection in the center. The two sides of the wire on opposite ends of this connection are called the two “poles.” Dipole radio antennas are very efficient for their small size, but typically have limited one-directional range. They are widely used as general purpose antennas.
Small handheld 2 way radios with short rubber antennas use the dipole design. Inside of these rubber antenna housings is a simple dipole wire. This gives handheld radios good multi-direction reception. Another common example of the dipole design is the “rabbit ear” antenna used on televisions. In this example, the two opposing “ears” are actually two ends of a dipole mounted in a V-shape, with the connection placed in the center.
Yagi Antenna
A Yagi antenna is essentially made of several dipole antennas linked together. The core of a Yagi design is a simple rigid dipole antenna placed horizontally, with a connection in the center. Another horizontal dipole antenna is placed at a 90-degree angle to the first wire, and shares the same connection point. Finally, two more horizontal dipole wires are connected to the ends of the original antenna. The result is an antenna that resembles a two “H” letters placed side-by-side.
Yagi antennas are very efficient at transmitting and receiving in one direction. This makes them useful for two-way radio communications where both stations are fixed locations, such as buildings or parked vehicles. The Yagi antenna design enables radio communication over longer distances than a simple dipole.

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