6
1.3.4 The footprint of the radiator
The number of transmitted carriers and the output
power of the radiator determine the coverage area of a
radiator. The total radiation energy of a radiator is
distributed over transmitted carriers. The coverage
area becomes proportionally smaller if more carriers
are used. The receiver requires a strength of the IR
signal of 4 mW/m
2
per carrier to work well (resulting in
an 80 dB S/N ratio for uninterrupted audio channels).
The cross section of the 3-dimensional radiation with
the reception level of participants is the footprint (the
dark grey area in figure 1.9 to figure 1.11). In this area,
the direct signal is strong enough to ensure proper
reception when the receiver is directed towards the
radiator.
The size and position of the footprint depends on the
mounting height and the angle of the radiator.
Figure 1.9 The radiator mounted at 15
°
to the ceiling
Figure 1.10 The radiator mounted at 30
°
to the ceiling
Figure 1.11 The radiator mounted perpendicular (at 90
°
)
to the ceiling
1.3.5 Positioning the radiators
Because infrared radiation can reach a receiver directly
and/or via diffused reflections, it’s important to take this
into consideration when installing the radiators. For
best reception quality, receivers should pick up direct
infrared radiation. In addition reflections will improve
the signal reception. In big conference halls, infrared
signal will be blocked by the people in front of the
receiver. For that reason the radiator should be
installed at an appropriate height, usually not below 2.5
meters.
For concentrically arranged conference venues,
radiators located high up and faced to the center from
every angle can cover the area very efficiently. If the
direction of the receiver changes, e.g. changing seat
direction, the radiators can be installed in the corners of
the room.
In the case of the seating is always directed towards
the IR emitting source, there are no radiators needed at
the back (see figure 1.12).
Figure 1.12 Radiator positioning in a conference hall
with auditorium seating and podium
