User Manual

SNB900 Radio Modem User Guide 23
Characteristics and Specifications 4
Figure 4.1 shows the radiated energy patterns of the omni-directional
antennas.
Figure 4.1 Omni-directional antenna gain patterns
The top view shows radiated energy patterns in the horizontal, or
azimuth plane of the antennas, the plane that perpendicularly bisects
the length of the antenna. For omni-directional antennas, all azimuths
receive equal energy, but the 5 dB antenna radiates almost four times
more power in the horizontal plane than the 0 dB antenna. In an open
field, four times more power approximately doubles the range.
Much of the energy from the 5 dB antenna is concentrated in elevation
to within ±12° of horizontal. A rover antenna within this sector
receives stronger signals from a 5 dB antenna. However, at angles
greater than 12° from horizontal, the 0 dB gain antenna radiates more
energy.
Antenna gain has exactly the same effect on signal reception as it does
on signal transmission. A high gain rover antenna can increase range
performance as long as it is oriented correctly with respect to the
transmitting antenna. For high gain antennas, this means keeping the
antenna element vertical and at the same elevation as the transmitting
antenna. Otherwise, it may be better to use an antenna with less gain.