User manual

Chapter Three Installation
MAN_905G_1.16 Page 28
antennas inside buildings. An obstructed path requires testing to determine if the path will be
reliable - refer the section 6 of this manual.
Where it is not possible to achieve reliable communications between two modules, then
another 905U or 905G module may be used to receive the message and re-transmit it. This
module is referred to as a repeater.
An antenna should be connected to the module via 50 ohm coaxial cable (eg RG58, RG213
or Cellfoil) 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. For use on unlicensed frequency channels, there are several
types of antennas suitable for use. It is important antenna are chosen carefully to avoid
contravening the maximum power limit on the unlicensed channel - if in doubt refer to an
authorized service provider.
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 permitted is
Country Max. gain (dB)
USA / Canada 6
Australia / New Zealand 0
The gains and losses of typical antennas are
Antenna Gain (dB) Elpro Part Nos.
Dipole with integral 15’ cable 0 CFD890EL
5dBi Collinear (3dBd) 5 SG900EL
8dBi Collinear (6dBd) 8 SG900-6
6 element Yagi 10 YU6/900
9 element Yagi 12
16 element Yagi 15 YU16/900
Cable type Loss (dB per 30 ft / 10 m)
RG58 -5
RG213 -2.5
Cellfoil -3 CC10/900 (33’ or 10m)
CC20/900 (66’ or 20m)
The net gain of the antenna/cable configuration is determined by adding the antenna gain and
the cable loss. For example, a 6 element Yagi with 66 feet (20 meters) of Cellfoil has a net
gain of 4dB (10dB – 6dB).
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, firstly 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 as the vulcanizing
seal can be easily removed.