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Cooper Bussmann 945U-E Wireless Ethernet Modem & Device Server User Manual
Rev Version 2.14
time delays. Using more than one antenna the radio is able to choose the best signal thus providing a more robust
radio link.
The second reason to use antennas diversity is to increase the received radio signal into the receiver. All countries
have radio licensing regulations that can often limit on the amount of transmitted power and radiated power from
the antenna. In the US this is 630 mW or 1000 mW for the 945U-E-H of transmit power and 4 watts EIRP (Effective
Isotropic Radiated Power) from the antenna. If a high gain antenna is used to try and improve the receive signal it
will also increase the transmit level and push it over the EIRP regulation limit.
Using Antenna diversity allows two antennas to be used, one for receive and the other for transmit / receive. The
TX / RX antenna has the normal restriction on gain to keep it below the regulation limit. However, the receive
antenna has no regulatory limits as it does not radiate power so a higher gain antenna can be used to receive
weaker signals. See “3.9 Advanced Radio Configuration” for details on configuring Antenna diversity.
In North America, the maximum allowable radiated power (EIRP) for a 945U-E is 4 Watts, which is 8 dB higher that
the modules transmit power of 630 mW or 6 dB higher that the transmit power of the 945U-E-H. Therefore we are
able to increase the antenna gain as long as overall system gain (antenna Gain – coax loss) does not go above 8 dB
for the 945U-E or 6 dB for the 945U-E-H.
Example
• Using the 945U-E with 10 m (33 ft) of Cellfoil coax cable (approximately 3 dB of loss) and an 8 dBi collinear
antenna would equate to approximately 5 dB of gain, which is below the regulated 8 dB limit.
• Using the 945U-E-H with 20 m (66 ft) of Cellfoil coax cable (approximately 6 dB of loss) and a 10 dBi Yagi
antenna would equate to approximately 4 dB of gain, which is below the regulated 6 dB limit.
Bench Test and Demo System Setup
Care must be taken with placement of antenna in relation to the radios and the other antennas. Strong radio signals
can saturate the receiver, hindering the overall radio communications.
When setting up a bench test, demo, or a short range system, the following considerations should be taken into
account for optimum radio performance and reduced signal saturation.
• If using Demo Whip antennas (DG-900 and WH-900), it is recommended that only the Access Point be fitted
with an antenna.
• If using Demo Whip antennas on each end, a 20 dB coax attenuator must be connected in-line with the coax
cable.
• If using Demo Whip antennas, modules and antennas must be kept a suitable distance from each other. Check
the receive signal strength on the Connectivity page of the module and ensure the level is not greater than
-45 dB.
Demo Whip antennas should not be used in the final installation as the maximum performance of the modem
cannot be guaranteed. If using a DG-900 antenna, it is better to keep the antennas at least 3 ft (1 m) away from the
module so as to limit RF saturation.
Plant and Factory Installations
Another application where antenna diversity may be needed is in industrial plants and factories installations which
can suffer from multipath fading effects where multiple reflected radio signals adversely affect the signal strength.
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 945U-E is mounted on moving equipment
or if there is moving equipment in the area, 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 945U-E unit
will automatically select the higher RF signal provided RX diversity has been enabled on the radio Configuration
page.