SATELLINE-3AS and SATELLINE-3ASd
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A sufficient safety margin can be obtained by testing communications using an extra 6 dB
rejection at the antenna connection and with slightly less effective antennas than those to be used
in the final system.
8.1.2
Radio field strength
A successful radio transmission depends essentially on the radio field. Where field strength is over
a certain level the operational results are very good. Below this level, a few dB marginal areas
may occur in which errors begin to be generated by noise and interference which will eventually
lead to loss of connection.
Whilst in an open space, the field strength is at its optimum level, although it will still be reduced
by distance. It must also be remembered that one open space has different environmental and
external factors to another, and that the affects on transmission quality must be taken into
account when planning the system.
Ground, ground contours and buildings cause attenuation (loss of energy through absorbtion)
and reflections of radio waves. Buildings reflect radio waves and therefore the affects of
attenuation are not as acute when transmission is over a short distance.
However, the reflected waves will suffer a loss in power once they travel over a certain distance,
this means that they combine with the direct radio waves and interact in either weakening or
strenghtening the signal respectively. In reality attenuation can even occur at 40 dB which is very
sharp and the effect on the 450 MHz frequency is about 35 cm difference.
