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245U-E Wireless Ethernet Modem User Manual
13
Rev Version 2.24
By default the right connector, labeled “TX/RX,” is the main connection used for transmitter and receiver.
The left connector, labeled “RX,” is not connected unless configured as described in “3.10 Advanced Radio
Configuration.” Each antenna port can be configured for TX only, RX only, or Diversity (TX and RX). Selection
can be made by choosing one of the options from TX Antenna / RX Antenna on the Advanced Radio
Configuration page.
NOTE When only one antenna is used, it must be connected to the TX/RX connector.
Antenna Diversity (Note: not available with 245U-E-A1 model)
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.