RTcom Radio Modems Manual de usuario descargar pdf (Pagina 9)

Antenna Options :

Antenna types fall to 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 not 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, a compressed dipole (helical) antenna can 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

vertical plane only.

For portable apparatus operating 400MHz

Requires a ground plane for operation.

Helical < -4dB to -10dB near omni in the

vertical plane only

For portable apparatus <-400MHz

Requires a ground plane for operation

1 /2 wave dipole +1.2 to +1.8dB near omni-directional

in the vertical plane.

For portable and fixed apparatus looking for a

low 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-directional in

vertical plane

For fixed apparatus that does not require a

ground plane

Yagi +3dB to +28dB. Beam width

proportional to gain

For point to point links. Where an unwanted

signal 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 Manual de usuario Pagina 9