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Cooper Bussmann BU-245U-E Wireless Ethernet & Device Server User Manual
Dual Antenna Installations
Most installations in industrial plants and factories use single omni-directional antennas. Installations can suffer from “
multi-path fading” effects where multiple reflected radio signals adversely affect the signal strength.This can be checked by moving the antenna a
short distance (10 cm or 4 inches) - if the signal increases significantly then there are multi-path effects.
In a “static”installation, where the radio path is not changing, moving an antenna to the position of maximum signal solves this problem. However
where the radio path changes because the BU-245U-E is mounted on moving equipment, or if there is moving equipment in the area,then the
solution is to use two antennas. Because the two connectors are separated,the RF signal at each connector will be different in the presence of
multi-path fading.The BU-245U-E unit will automatically select the higher RF signal provided RX diversity has been enabled on radio config page.
Note that directional antennas are not normally used in plant and factory installations.
Another reason for using dual antenna is to improve the receiver gain.All countries have a limit on the amount of transmitted power (from the
module) and radiated power (from the antenna). In the US this is 1 Watt Transmit power and 4 watts EIRP (Effective Isotropic Radiated Power)
A general rule of thumb when working with dB and Power is to remember that doubling the Power is a 3dB gain.
Therefore if we add a 6dB gain antenna to the 1 Watt transmitter we can boost the EIRP to 4 Watts (1 watt
Line-of-Sight Installations
In longer line-of-sight installations, the range may be increased by using a high gain antenna on the TX/RX connector.However, the gain should
not cause the effective radiated power (ERP) to exceed the permitted value.A second higher gain antenna can be connected to the RX connector
without affecting ERP - this will increase the operating range provided any interference in the direction of the link is low.
Antennas
Antennas can be either connected directly to the module connectors or connected via 50 ohm coaxial cable (e.g. RG58 Cellfoil or RG213)
terminated with a male SMA coaxial connector.The higher the antenna is mounted, the greater the transmission range will be, however as the
length of coaxial cable increases so do cable losses.
The net gain of an antenna/cable configuration is the gain of the antenna (in dBi) less the loss in the coaxial cable (in dB).The maximum net gain
of the antenna/cable configuration connected to the TX/RX connector is 0dB in Europe (100mW ERP).In USA, Canada and Australia (4W ERP), the
maximum gain is 10dB for the BU-245U-E-400 or 16dB for the BU-245U-E-100.
There is no gain restriction for antennas connected to the RX connector.
(*) 20dB attenuator must be fitted if radio distance is less than 33ft (10m).
Antenna BU-245U-E-G Gain (dBi) BU-245U-E-A Gain (dBi)
Dipole 2 dBi 6 dBi
Collinear 5 or 10 dBi 10 dBi
Directional 18 dBi 10 – 20 dBi
Cable Loss dB per 30 m / 100 ft dB per 30 m / 100 ft
RG58 Cellfoil -17 dB -24.5 dB
RG213 -16.2 dB -28.6 dB
LDF4-50 -3.6 dB -5.5 dB
The net gain of the antenna/cable configuration is determined by adding the antenna gain and the cable loss.
For example, if using the BU-245U-E-G a 10dBi antenna (7.8dBd) with 10 meters of Cellfoil (-5.6dB) has a net gain of 2.2dB (7.8dB – 5.6dB).
3A1576Rev1.6