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in the range of -25…-70dBm. Lower than -70dBm will work too, but packet losses may start
occurring. The quality of radio connection very much depends on the external interference too,
because the used band is ISM and there are many systems co-existing.
6.4
Deep hints
Avoid placing beacons on long sound conducting objects
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This is a very rare case, but may happen in some special circumstances
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The best practice is to place beacons (stationary and mobile) in such places that would not result
in transferring ultrasound energy from the beacon’s board/case directly to place it is attached via
other medium than air. For example, solid attachment of a beacon to a long horizontal metal
tube may result in the following:
Sound emitted from the beacon propagates directly to the metal tube
Propagation loses inside metal are much smaller than in the air. Moreover, the tube
may act as a low-loss waveguide
If the tube is solid enough and long enough, there may be a weird effect when the
receiving beacon receives the signal sooner than expected, i.e sooner than the
distance divided by the speed of sound in air. That happens because of speed of
sound in metal is much higher than speed of sound in the air and some part of the
path the sound travelled in the metal. The ultrasound signal may even look stronger
than the real signal propagated through the air due to lower losses of ultrasonic in
metal than that in the air
It is good practice to place beacons on something relatively soft or not so sound
conductive