User`s manual

A2500R24x – User’s Manual Page 19 of 35
Release Date 09/05/12
Some of the most common interferences are listed below.
2.2.1. WLAN
Wireless Local Area Networks (WLANs) are divided into a number of overlapping channels.
Figure 5 below shows the channels used by WLAN; for the US and Canada, only channels 1-13
may be used. Predominantly, channels 1, 6 and 11 are used to achieve non-overlapping
channels. The user is therefore encouraged to select a channel scheme that also has channels
falling in between, or entirely outside, WLAN channels. Using a detection scheme (clear channel
assessment) will enable the user to find channels with minimal interference from WLAN devices.
Figure 5 WLAN channels
2.2.2. Bluetooth
®
Bluetooth
®
divides the 2.402-2.480 GHz band into 79 channels, each of which is 1MHz wide.
However, since Bluetooth
®
changes channels rapidly (up to 1600 times a second), it is unlikely
to cause continuous interference in a specific channel and can be overcome by implementing a
simple acknowledge/retransmit functionality.
2.2.3. Microwave ovens
A typical microwave oven uses a self-oscillating magnetron with a duty cycle below 50%,
because the tube is completely off for half of every AC mains cycle (8.33 ms in 60 Hz countries
and 10 ms in 50 Hz countries). The frequency of the microwave oven changes cyclically within
each AC mains synchronized on period, and is generally not predictable.
The user is encouraged to have packet transmission durations less than half the AC mains
period and implement an acknowledge/retransmit method.
2.2.4. Other Interference
Systems similar to the user’s system may also exist within range and may also be a source of
interference; some typical applications to consider are:
 Alarm systems
o These typically use low duty cycles and are therefore easy to avoid using
acknowledge/retransmit methods
 Car alarms (internal motion sensors)
 Video surveillance