Using with Campbell Scientific Dataloggers
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 COM110
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 COM110 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 COM110 modem. If you call the COM110 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 COM110 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.
If you cannot use a base station GSM modem, lower cost calls may also be
possible by programming the datalogger to call back to the land-line phone base
station, as the special airtime rates will normally apply to such calls too.
NOTE
NOTE
7
