1.4 Factors impacting infrared signal transmission
To benefit from the advantages of a digital infrared
wireless classroom audio system the signals should be
transmitted undisturbed. This is achieved by using
digital infrared receiver well positioned and sufficient in
quantity to ensure uniform and adequate infrared
radiation for all microphones.
When planning a digital infrared wireless classroom
audio system, several aspects influencing the
uniformity and quality of the infrared signal should be
considered. These are discussed in the next sections.
1.4.1 Ambient lighting
TES-5600 system adopts 1-8 MHz wave band, and has
a good anti-interference performance (see figure 1.3).
Figure 1.3 Digital infrared classroom audio system with
1-8 MHz wave band can avoid high frequency lights
disturbance
For classrooms with large, unscreened windows,
multi-receiver operation should be considered. For
outdoor using, a site test will be required to determine
the needed amount of receivers. With sufficient
receivers, perfect signal transmission can be fulfilled
even in bright sunlight.
1.4.2 Objects, surfaces and reflections
Just like visible light, infrared radiation is reflected from
hard surfaces and refracted by hyaloid (glassy or
transparent appearance) items. Objects in the
classroom as well as structure of the walls and ceilings
will influence the distribution of infrared light.
Infrared radiation is reflected from almost all hard
surfaces. Smooth, bright or shiny surfaces reflect well.
Dark or rough surfaces absorb a large part of the
infrared energy. Usually, surfaces opaque to visible
light are also opaque to infrared radiation.
Shadows from walls and furniture will influence the
transmission of infrared light. This can be solved by
using a sufficient quantity of receivers. They should be
positioned in a manner to provide an infrared field
strong enough to cover the whole teaching area.
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