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© Copyright 2007 Trio DataCom Pty. Ltd.
O Series Data Radio – User Manual
Part D – System Planning and Design
Antenna Placement
When mounting the antenna, it is necessary to consider the
following criteria:
The mounting structure will need to be solid enough to withstand
additional loading on the antenna mount due to extreme wind, ice
or snow (and in some cases, large birds).
For omni directional antennas, it is necessary to consider the
effect of the mounting structure (tower mast or building) on the
radiation pattern. Close in structures, particularly steel structures,
can alter the radiation pattern of the antenna. Where possible,
omni antennas should always be mounted on the top of the mast
or pole to minimise this effect. If this is not possible, mount the
antenna on a horizontal outrigger to get it at least 1-2m away from
the structure. When mounting on buildings, a small mast or pole
(2-4m) can significantly improve the radiation pattern by providing
clearance from the building structure.
For directional antennas, it is generally only necessary to consider
the structure in relation to the forward radiation pattern of the
antenna, unless the structure is metallic, and of a solid nature.
In this case it is also prudent to position the antenna as far away
from the structure as is practical. With directional antennas, it is
also necessary to ensure that the antenna cannot move in such
a way that the directional beamwidth will be affected. For long
yagi antennas, it is often necessary to install a fibreglass strut to
stablilise the antenna under windy conditions.
Alignment of Directional Antennas
This is generally performed by altering the alignment of the
antenna whilst measuring the received signal strength. If the
signal is weak, it may be necessary to pre-align the antenna using
a compass, GPS, visual or map guidance in order to “find” the
wanted signal. Yagi antennas have a number of lower gain “lobes”
centred around the primary lobe. When aligning for best signal
strength, it is important to scan the antenna through at least 90
degrees, to ensure that the centre (strongest) lobe is identified.
When aligning a directional antenna, avoid placing your hands or
body in the vicinity of the radiating element or the forward beam
pattern, as this will affect the performance of the antenna.
Common Cable Types
Loss per 30.5m
Loss per 30.5m
@ 915MHz
@ 2.4GHz
RG213/U
7.4dB
23.6dB
FSJ1-50 (¼” superflex)
5.6dB
9.9dB
LDF4-50 (1/2” heliax)
2.2dB
2.3dB
LDF5-50 (7/8” heliax)
1.2dB
3.7dB
RF Feeders and Protection
The antenna is connected to the radio modem by way of an
RF feeder. In choosing the feeder type, one must compromise
between the loss caused by the feeder, and the cost, flexibility, and
bulk of lower loss feeders. To do this, it is often prudent to perform
path analysis first, in order to determine how much “spare” signal
can be allowed to be lost in the feeder. The feeder is also a critical
part of the lightning protection system.
All elevated antennas may be exposed to induced or direct
lightning strikes, and correct grounding of the feeder and mast are
an essential part of this process. Gas discharge lightning arresters
should also be fitted to all sites.
Note: All ETSI installations require the use of a lightning surge
arrestor in order to meet EN6095.
