Instruction 5700-9001
GDA-1600 16-Channel Controller
49
Radio Kit. Other Modbus slave devices may also be converted to wireless by addition of
another Radio Kit at the slave’s location.
8.5 Antenna Selection
8.5.1 Dipole and Collinear Antennas
These antennas are connected to the Radio via a length of coax cable. If the cable is
larger than 6mm diameter (1/4 inch), do not connect the cable directly to the radio
connection on the GDA-1600 enclosure. Thick cables have large bending radii and
sideways force on the connector can cause a poor connection. Use a short flexible pigtail
between the thick cable and the radio.
The polarity of these antennas is the same as the main axis, and they are normally
installed vertically. They can be mounted horizontally (horizontal polarity), however the
antenna at the other end of the wireless link would need to be mounted perfectly parallel
for optimum performance. This is very difficult to achieve over distance. If the antenna
is mounted vertically, it is only necessary to mount the other antennas vertically for
optimum “coupling” – this is easy to achieve.
Dipole and collinear antennas provide best performance when installed with at least 1 to
2 “wavelengths” clearance of walls or steelwork. The wavelength is based on the
frequency:
Wavelength in meters = 300 / frequency in MHz
Wavelength in feet = 1000 / frequency in MHz
Therefore, 900 MHZ antennas require at least 2/3 meter (2 feet) and 2.4GHz 15 cm
(6 inches). Antennas may be mounted with less clearance, but radiation will be reduced.
It is important for the antenna mounting bracket to be well-connected to “earth” or
“ground” for good lightning surge protection.
8.5.2
Yagi Antennas
Yagi antennas are directional along the central beam of the antenna. The folded element
is towards the back and the antenna should be “pointed” in the direction of the
transmission. Yagis should also be mounted with at least 1 to 2 wavelengths of clearance
from other objects. The polarity of the antenna is the same as the direction of the
orthogonal elements. For example, if the elements are vertical the Yagi transmits with
vertical polarity.
In networks spread over wide areas, it is common for a central unit to have an omni-
directional antenna and the remote units to have Yagi antennas. In this case, as the omni-
directional antenna will be mounted with vertical polarity, then the Yagis must also have
vertical polarity. Care needs to be taken to ensure the Yagi is aligned correctly to achieve
optimum performance.
Two Yagis can be used for a point-to-point link. In this case they can be mounted with
the elements horizontally to give horizontal polarity. There is a large degree of RF
isolation between horizontal and vertical polarity (approx –30dB) so this installation
Summary of Contents for GDA-1600
Page 21: ...Instruction 5700 9001 GDA 1600 16 Channel Controller 21 Figure 3 10 Configuration Menus ...
Page 28: ...GDA 1600 16 Channel Controller Instruction 5700 9001 28 Figure 4 2 Main PCB ...
Page 36: ...GDA 1600 16 Channel Controller Instruction 5700 9001 36 Figure 4 7 Analog Output Board ...
Page 38: ...GDA 1600 16 Channel Controller Instruction 5700 9001 38 Figure 5 2 System Diagnostic Options ...
Page 53: ...Instruction 5700 9001 GDA 1600 16 Channel Controller 53 ...
