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Cooper Bussmann 245U-E Wireless Ethernet Modem & Device Server User Manual
13
Rev Version 2.19
Antenna Diversity
One reason to use multi-antennas is to comply with local radio licensing regulations. All countries have a limit on
the amount of transmitted power and radiated power from the antenna. In the US this is 400-millwatts transmit
power and 4-watts EIRP (effective isotropic radiated power). See “3.10 Advanced Radio Configuration” for details
on configuring antenna diversity
In North America, the maximum allowable radiated power (EIRP) for a 245U-E-G is 4 W, which is 10 dB higher that
the modules transmit power of 400 mW. Therefore, you can increase the antenna gain as long as the overall system
gain (antenna gain, coax loss) does not rise above 10 dB.
Example
• Using the 245U-E with a 10 m (33 ft) Cellfoil coax cable (approximately 6 dB of loss) and an 8-dBi gain antenna
would equate to approximately 2 dB of gain, which is well below the 10 dB limit.
• Using the 245U-E with a 20 m (66 ft) Cellfoil coax cable (approximately 12 dB of loss) and an 18-dBi antenna
would equate to approximately 6 dB of gain, which is also below the 10 dB limit.
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 (such
as RG58 Cellfoil or RG213) terminated with a male SMA coaxial connector. The higher the antenna is mounted, the
greater the transmission range. However, cable losses also increase as the length of the coaxial cable increases.
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 0 dB in
Europe (100 mW ERP). In USA, Canada and Australia (4 W ERP), the maximum gain is 10 dB for the 245U-E-400
and 16 dB for the 245U-E-100.
There is no gain restriction for antennas connected to the RX connector.
Antenna
245U-E-G Gain (dBi)
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
NOTE 20 dB attenuator must be fitted if radio distance is less than 33 ft (10 m).
The net gain of the antenna/cable configuration is determined by adding the antenna gain and the cable loss. For
example, using the 245U-E-G a 10 dBi antenna (7.8 dBd) with 10 meters of Cellfoil (-5.6 dB) has a net gain of
2.2 dB (7.8 dB – 5.6 dB).
Installation Tips
Connections between the antenna and coaxial cable should be carefully taped to prevent ingress of moisture.
Moisture ingress in the coaxial cable is a common cause for problems with radio systems, as it greatly increases
the radio losses. We recommend that the connection be taped, first with a layer of PVC tape, then with a
vulcanizing tape such as 3M™ 23 tape, and finally with another layer of PVC UV-stabilized insulating tape. The
first layer of tape allows the joint to be easily inspected when trouble shooting because the vulcanizing seal can be
