Westermo RM-455U-D User Manual
Page 21
455U-D Radio Modem
User Manual
Page 22 © May 2010
some obstruction of the radio path. Obstructions which are close to either antenna will have
more of a blocking effect than obstructions in the middle of the radio path. For example, a
group of trees around the antenna is a large obstruction, and the antenna should be raised
above the trees. However if there is at least 100 meters (300 feet) of clear path before a group
of trees, the trees will have less affect on the radio path. To help in planning radio systems,
ELPRO provides a free utility for estimating path performance.
The modules provide test diagnostics to test the radio path and display radio signal strength.
An antenna should be connected to the module via 50 ohm coaxial cable (eg RG58, Cellfoil or
RG213) terminated with a male SMA 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. For use on unlicensed frequency channels, there are several types of antennas
suitable for use. It is important antennas are chosen carefully to avoid contravening the
maximum allowed power limit on the on the radio channel - if in doubt refer to a authorized
ELPRO distributor in your country or email ELPRO on [email protected].
The gains and losses of some typical antennas and cable types are
Antenna Gain
(dB)
Dipole with integral cable
0
3dBd Collinear
5
6dBd Collinear
8
6 element Yagi
9
9 element Yagi
12
16 element Yagi
15
Cable type
Loss (dB per 10 m)
RG58 -4.5
RG213 -1.65
Cellfoil -2.25
The net gain of the antenna/cable configuration is determined by adding the antenna gain and
the cable loss. For example, a 6dBd Collinear with 20 metres of RG58 has a net loss of 1 dB
(8dB – ((20/10) x 4.5) dB) = 8dB – 9dB = -1dB
Another important consideration when installing the antenna system is RF exposure. The
antenna can radiate a large amount of RF energy. It is important to ensure that a person
cannot approach the antennas within the recommended minimum safe distances in the table
below.