905U Wireless I/O Module User Manual
105S Serial I/O Module
Page 12 © January 2011
the antenna is a larger obstruction than a group of trees further away from the antenna. The 905U
modules provide a test feature which displays the radio signal strength.
Line-of-sight paths are only necessary to obtain the maximum range. Obstructions will reduce the
range however, but may not prevent a reliable path. A larger amount of obstruction can be tolerated for
shorter distances. For very short distances, it is possible to mount the antennas inside buildings. An
obstructed path requires testing to determine if the path will be reliable - refer the section 6 of this
manual.
Longer distances can be achieved using the licensed 105U units, because they use a lower frequency
and licensed conditions generally allow a higher RF power to be used.
Where it is not possible to achieve reliable communications between two modules, then a third module
may be used to receive the message and re-transmit it. This module is referred to as a repeater. This
module may also have input/output (I/O) signals connected to it and form part of the I/O network -
refer to Chapter 4 Configuration of this manual.
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 authorised 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 for 905U is
Country Max. gain (dB)
USA / Canada 6
Australia / New Zealand 0
The gains and losses of typical antennas for 905U are
Standard Antennas 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 YU9/900
16 element Yagi 15 YU16/900
Cable type Loss (dB per 30 ft / 10 m)
RG58 -5
RG213 -2.5
Cellfoil -3
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