RTcom Radio Modems user manual Antenna Types

Models: Radio Modems

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Warning: The use of gain antenna in some countries is not permitted. Similarly where ERP (transmitted power limits) are imposed the actual transmitted power must not exceed the limit stated. This means that the transmitter output power, less any coaxial feeder losses, plus the antenna gain must not exceed the specified maximum ERP. Before installing your system please check!

Antenna Types

Antenna types fall into a number of categories. For the majority of applications the choice lies between portable, fixed, omni-directional and those with gain and directional properties.

True omni-directional antenna in reality do no exist, i.e. those with equal gain in all directions. However the nearest practical equivalent is the 1/2 or 1/4 wave dipole. The 1/4 wave dipole is by far the most popular of all antennas and is found in use on most portable apparatus. Where the frequency is too low and the dipole can become cumbersome and a compressed dipole (helical) antenna has to be used.

Whatever antenna types you choose please ensure that its impedance is 50 Ohms.

name

Gain and Directional Properties

Comments

 

 

 

1/4 wave dipole

< -0.8dB near omni in the

For portable apparatus operating above 400MHz

 

vertical plane only.

Requires a ground plane for operation

 

 

 

Helical

< -4 to -10dB near omni in the

For portable apparatus < 400MHz

 

vertical plane only.

Requires a ground plane for operation

 

 

 

1/2 wave dipole

+ 1.2 to + 1.8dB near omni-

For portable and fixed apparatus looking for a low

 

directional in the vertical plane.

cost antenna that does not require a ground plane

 

 

 

End fed dipole

0db, near omni in vertical plane

For fixed apparatus that does not require a ground

 

 

plane

 

 

 

Colinear

+3dB to +9dB , near omni-

For fixed apparatus that does not require a ground

 

directional in vertical plane

plane

 

 

 

Yagi

+3dB to +28dB . Beam width

For point to point links. Where an unwanted signal

 

proportional to gain

needs to be blocked from the opposite direction

 

 

choose an antenna with a high front to back ratio

 

 

 

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RTcom Radio Modems user manual Antenna Types