2013年1月6日星期日

Types of 2 Way Radio Antennas

Omni Antenna
An omni, or “omni-directional” antenna, is made from a dipole antenna wire that has had its two ends bent into a curved shape. This antenna resembles the shape of the letter “S.” By bending the poles of the dipole antenna, the maximum receiving range is reduced, but nearby omni-directional signal strength is improved.
An omni antenna is used in 2 way radio situations where all communication will will take place near one small area, such as a base or outpost. The omni design allows radios in any direction near the base station to be easily reached. Cell phone towers also commonly use omni antennas. This enables a cell phone radio signal to reach a nearby tower from any direction, and even if the user is moving.
Parabolic Antenna
A parabolic antenna design combines a simple dipole with a semi-circular dish. Just as a magnifying glass can focus light to a precise point, the curved dish reflects radio signals directly onto the dipole. The most common example of a parabolic antenna is the home satellite dish, however the design can be used in other two-way radio applications as well.
Parabolic antennas are used for two-way communication over extremely long distances, and are usually able to transmit farther than a Yagi design. The parabolic antenna type is only useful if the exact location of the target receiver is known. Parabolic antennas are frequently used for two-way satellite links, long-range wireless Internet, and two-way radio communication between fixed stations.

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