Using with Campbell Scientific Dataloggers
7
ensure proper impedance matching. As an approximate rule the ground plane
should have a radius equal to or greater than the height of the radiator.
•
Slightly higher priced co-linear, ‘marine’-grade antennae do not require such a
ground plane and can be more easily pole or cross-arm mounted.
•
In areas of poor signal coverage a directional, high-gain ‘Yagi’ antenna can be
considered, but this requires knowledge of where the cell base stations are
situated in order to enable proper alignment.
•
Raising the antenna is often the most effective way of getting better signal
reception. However, if long cables are required to achieve this, use low-loss
extension cables that do not have the significant signal loss of cheaper cables.
Long cables are a particular problem when operating at 1800MHz.
•
Like most cellular-based systems, the TC35T varies its transmitter power to
ensure good communications with the remote cell station. Using a cheaper,
low-gain, antenna may result in a significant increase in power consumption in
areas of poor signal coverage.
•
If the antenna is placed near the top of a mast it may be vulnerable to lightning
damage. If lightning is common at the installation site, additional lightning
protection may be required to protect the TC35T – please contact Campbell
Scientific for further advice.
Using an antenna that is installed incorrectly, or with faulty
wiring, can lead to premature failure of the transmitter output
of the TC35T.
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 TC35T is
connected to a PC (see below) it is possible to check the received signal strength
using the
AT+CSQ
command (see Appendix C or the TC35T manual 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. Be sure that the module is configured to talk only to the
network operator you intend to use when doing this (see the
AT+COPS
command).
Many antennae 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 TC35T to
the power supply ground via the lightning protection cables
and mounting structure.
5.1 Antenna Supplied by Campbell Scientific
Campbell Scientific can supply various antennas, if required, including a ‘low-
cost’ antenna (see Figure 4, below).
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 directly fit the TC35T transceiver aerial
socket. 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.
CAUTION
CAUTION
