SATELLINE-3AS
User Guide, Version 2.3
53
8 Diversity receiver (SATELLINE-3AS Epic only)
SATELLINE-3AS Epic model has two antenna connectors, one solely for reception and the other
for both reception and transmission. Diversity reception means that the radio modem selects the
best signal from both those received by the two antennas. In this way the reliability of the
connection is improved especially in those cases which are subject to a high level of reflections
and multipath fading.
8.1 Multipath fading
In radio systems (operating at suitable frequencies) it is not necessary to have a direct line-of-
sight connection between the master station and a moving substation, because the radio signal
propagates by reflecting from buildings and terrain contours e.g. hills. These useful reflections
do however cause fading, which can occur when the radio signal experiences a number of
reflections on the way to the receiving antenna. Radio signals propagate at the speed of light
but if the signal is reflected from several different objects before reaching the receiving antenna
the different total path lengths of these reflected signals will cause them to be detected at slightly
different times. This means that these detected reflected signals are in different phases. In the
worst case scenario, two equally strong signals are in exactly opposing phases thus cancelling
each other out and causing the signal level to drop.
The received signals from two antennas. The selected signals are marked in grey.
R
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B
Time
The chance that two fades occur
at the same time is low
Quality measurement every 1 or 12 bytes
Signal threshold level
