7
If the path of the infrared signals is blocked, e.g. under
balconies, at least one additional radiator is needed to
cover the ‘shaded’ area (see figure 1.13).
Figure 1.13 Radiator for covering seats beneath a
balcony
1.3.6 Overlapped footprints and multipath
effects
If footprints of two radiators overlap, the total coverage
area maybe larger than the sum of the two separate
footprints. In an area with overlap effect, the individual
radiation signals of two radiators are added, resulting in
an increase of the radiation intensity, larger than the
required intensity.
However, due to the differences in the delays of the
signals from two or more radiators, the signals may
cancel out each other (multipath effect). In a
worst-case situation, loss of reception at some
positions (black spots) may be the consequence.
Figure 1.14 and figure 1.15 illustrate the effect of
overlapped footprints and differences in signal delays.
Figure 1.14 Increased coverage area caused by added
radiation power
Figure 1.15 Reduced coverage area caused by
differences in cable signal delay
The lower the carrier frequency, the less susceptible
the receiver is for differences in signal delays.
The signal delays can be compensated by adjusting
the delay compensation switches on the radiators (see
section 3.7).
