CS-3G Digital Transceiver Kits (including the COM111 modem)
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6.3 Connecting power
The COM111 modem requires a power supply capable of supplying 5-32V
DC, at an average current of up to 400 mA, with short peak currents of 2.5A
(at 5.5 V supply). COM111 is fitted with a 2A slow acting, fuse in an inline
fuse holder in its power cable, to minimise damage in the event of a failure.
The normal colour scheme for wiring is RED for positive and BLACK for
negative. If the COM111 modem is to be powered from the same supply as
the data logger, ensure that the power connections for the COM111 modem
are made as close as possible to the battery outputs. This will prevent the
COM111 modem causing voltage drops and noise on the supply to the data
logger.
The quiescent power consumption of the COM111 modem is typically
around 5 -15 mA, once the unit automatically shuts down at the end of a call.
For very low power installations turning the power off may be essential
though. To do this it is possible to control the power supply to the COM111
modem by using a solid state relay, such as the PSW12 power switch or, if
free, to use the power switch built into the wiring panel of some dataloggers.
See Appendix A for example programs where the data logger controls power
to the COM111. Table 1 shows the wiring from the PSW12 power switch to
the data logger. The failsafe wire, if connected to 5V, ensure the modem
remains powered if the logger program stops running and the control port the
yellow power control wire is connected to is not driven.
Table 1. COM111 Modem Power Supply Connections via a
PSW12 switch
COM111 modem Cable Colour
Connection
Red (positive supply)
+ 12V
Black (negative supply)
G
Yellow (power control)
Control Port (or +12V for testing)
White (Failsafe function)
5V (normally)
N.B. These colours and connections only apply to the cable supplied by Campbell Scientific
Ltd.
In the case of CR10X dataloggers, only the power switch in
wiring panels fitted with
green terminal blocks
is suitable.
6.4 Selecting and connecting an antenna
When selecting an antenna, please note the following points:
Make sure the antenna used covers the frequency you intend to use the
COM111 modem on, i.e. does the antenna cover 900, 1800 MHz
(common 2G frequencies, 900 or 2100 MHz (common 3G frequencies)
or some combination of them. Check the with your service provider
which frequencies will be in use at the installation site. Also check the
gain of the antenna at that frequency as many so-called high gain
wideband antenna are optimised for one band.
Low cost,
¼
- or
½
-wave antennae are adequate for most applications
where signal coverage is good. It is important to realise that most low
NOTE