Using with Campbell Scientific Dataloggers
17
Install the antenna so that the radiator is positioned away from other vertical metal
structures. It should also be at a distance from any sensors so that it does not either
physically or electrically interfere with the sensor readings. If the COM110A
modem is connected to a PC (see below) it is possible to check the received signal
strength using the
AT+CSQ
command (see Appendix C for further details). This
can be used to find the optimum antenna position. You should aim to get the
highest signal strength (as close to 31) as possible. For reasonable
communications you need a minimum level of approximately 10 when operating
in non-transparent mode for dial-up or 12-14 for GPRS use. Be sure that the
modem is configured to talk only to the network operator you intend to use when
doing this (see the
AT+COPS
command).
Many antenna have bodies that are connected to the coaxial
cable screen. It is therefore essential to ensure the correct
polarity is maintained through the cabling system to avoid the
possibility of shorting the transmitter output of the COM110A
modem to the power supply ground via the lightning
protection cables and mounting structure.
6.4.1 Antenna Supplied by Campbell Scientific
Campbell Scientific can supply various antennas, if required; including a ‘low-
cost’ antenna (see Figure 2, below). This is supplied as part of the standard CS-
GSM/GPRS package.
In areas of high signal strength, the low-cost antenna will be suitable for almost all
applications, either at 900 or 1800 MHz. The antenna, as supplied ‘off the shelf’,
is fitted with a connector which will either directly fit the COM110A modem
transceiver aerial socket or plug into an adaptor that will be supplied. When the
antenna is supplied as part of a weather station or other complete installation,
Campbell Scientific may replace the original connector with a compatible
connector before the system is tested.
In a field installation it is recommended that the cable length between the antenna
and the transceiver is kept as short as possible to reduce the signal loss in the
cable, although, as mentioned above, it is often more advantageous to mount the
antenna higher. In some applications the cable will need to be shortened, and so a
new connector can be installed onto the cable at this time by cutting off the surplus
cable, together with the original connector, and fitting a new connector. Ensure
that all connections are well made, and the connector is secured using a crimping
tool or pliers. The connector which connects to the modem is only suitable for use
in dry environments and so must be protected from direct exposure to water and
precipitation.
CAUTION
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