User manual

Using with Campbell Scientific Dataloggers
7
mode (see Appendix D for more information). Your airtime provider will
normally supply you with an extra phone number for the SIM specifically for data
use.
4.1 Network Coverage
One of the main advantages of using a cellphone network is being able to set up a
communications link to a datalogger virtually anywhere without installing land or
telephone lines. However, this only applies if a suitable GSM network covers your
installation site.
Within the UK the coverage of GSM networks is good in most areas. However,
coverage in remote areas can still be quite poor and is not likely to improve, as it
offers little commercial advantage to the network companies. Unless coverage is
known to be good at the proposed site, we strongly recommended that you test the
coverage using a standard GSM handset (on the same network as the COM110A
modem is to be used) to measure the exact signal strength.
Even areas shown as having good coverage on network maps can
have ‘holes’ due to local interference or other technical reasons, so
site testing is recommended.
In areas of normal signal strength the COM110A modem can be used with a
small, low cost antenna (as supplied in the CS-GSM/GPRS package). However, if
the signal strength is marginal it may be possible to improve reception using a
raised and/or a higher gain antenna. Poor quality reception will normally lead to
breaks in communication or result in the PC software having to make multiple
requests to ensure uncorrupted data is collected. This will not usually lead to data
loss or corruption, but may result in longer calls and thus higher call charges.
The network maintainer will be able to offer advice on coverage problems.
Campbell Scientific can also offer further advice on suitable antennae to suit the
application.
4.2 GSM data call charges
Call charges on cellular-based phones are usually much higher than landline based
systems and can therefore be quite high for a long-term data collection campaign.
Careful choice of the tariffs available can result in a considerable reduction in the
total bill.
One major factor, which can determine call costs, is the method used to connect to
the remote COM110A modem. If you call the COM110A modem from a landline
phone modem, you will normally pay your landline phone company the same
(high) cost as calling a voice cellphone. This is independent of your agreement
with the cellphone airtime provider. In many cases it may be cheaper to buy an
extra COM110A modem or another GSM phone for your base station, thus
avoiding the use of the land-based phone line altogether. Also, the set-up time
from a GSM to GSM modem is usually much lower and the overall call will thus
be shorter and thus cost less.
When selecting a tariff beware that most data tariffs relate to GPRS
data transfer, not dial-up, C.S.D. data transfer.
NOTE
NOTE