A client is installing a GSM/GPRS modem connected to an
electricity meter in the basement of a block of flats. GSM/GPRS networks work
on a line of sight principle i.e the modem antenna needs to have a direct view
of the base station via an M2M antenna If obstacles are in the way, some signal
is absorbed. The amount of signal absorbed depends on the materials of the
building. A plasterboard building would not absorb much signal whereas a
basement with several layers of concrete floors above would absorb a lot of
signal.
In this instance, we would expect poor performance from the
modem in terms of cellsites seen with a localized M2M antenna so there are 3
considerations to think about.
USE A HIGH GAIN ANTENNA
Much focus has been made to produce smaller M2M antennas for
discrete designs. There are many modelling software packages to design these
sorts of antennas but they should be left to the cellular handset market who
have to produce something at the lowest possible cost. Quality of Service is
not essential in the consumer market however for an alarm panel supplier - it
probably is. Compare an iPhone cellular performance with a 5110 and using the
sensible stub antenna versus an embedded antenna and the signal results are
evident.
The wavelength of the signal from the era of the Nokia 5110
to the iPhone has not changed. Vodafone for instance have always operated on
900MHz, and the length of the antenna is relative in order to pick up the
900MHz signal. As a rule of thumb, the bigger physical size the antenna is
(providing it is tuned to the frequency) the better the antenna should work as
it is relative to the wavelength of the frequency.
Taking the 900MHz centre frequency, a quarterwave length is
7cm and a half wavelength 30cm. A halfwave length will provide approximately
3dB (5dBi) of gain. This gain improves the signal performance being received
and is therefore a good thing.
PLACEMENT OF ANTENNA
As mentioned previously, GSM/GPRS (and most of today's
wireless equipment) operate on a line of sight basis. Therefore the installer
would need to consider mounting the M2M antenna as high above the ground as
possible to increase the chances of the M2M antenna being visible to the cell
tower. In the instance of a basement installation, trying to get it above
ground level is a challenge enough and in this instance cable is key.
CABLE LENGTH
Radio signal travelling along cable is susceptible to loss
in the same way as listening to an AM station in the car and travelling through
a tunnel, the station signal reception is lost until you reach the other side.
Different cables have different loss levels and higher frequencies have worse
loss characteristics than lower frequencies. For instance, the UK cellular
networks is made up of 4 main players.For more information about 3g Router ,Gsm Router,4g Lte Router and Lte Modem please visit my website.
