Sierra Wireless AirPrime EM8805, Руководство по интеграции оборудования

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Hardware Integration Guide
14 Proprietary and Confidential - Contents subject to change 4112940
Interference from other wireless devices
Wireless devices operating inside the host device can cause interference that
affects the module.
To determine the most suitable locations for antennas on your host device,
evaluate each wireless device’s radio system, considering the following:
• Any harmonics, sub-harmonics, or cross-products of signals generated by
wireless devices that fall in the module’s Rx range may cause spurious
response, resulting in decreased Rx performance.
• The Tx power and corresponding broadband noise of other wireless devices
may overload or increase the noise floor of the module’s receiver, resulting in
Rx desense.
The severity of this interference depends on the closeness of the other antennas
to the module’s antenna. To determine suitable locations for each wireless
device’s antenna, thoroughly evaluate your host device’s design.
Host-generated RF interference
All electronic computing devices generate RF interference that can negatively
affect the receive sensitivity of the module.
Proximity of host electronics to the antenna in wireless devices can contribute to
decreased Rx performance. Components that are most likely to cause this
include:
• Microprocessor and memory
• Display panel and display drivers
• Switching-mode power supplies
Device-generated RF interference
The module can cause interference with other devices. Wireless devices such as
AirPrime embedded modules transmit in bursts (pulse transients) for set durations
(RF burst frequencies). Hearing aids and speakers convert these burst
frequencies into audible frequencies, resulting in audible noise.
Methods to mitigate decreased Rx performance
It is important to investigate sources of localized interference early in the design
cycle. To reduce the effect of device-generated RF on Rx performance:
• Put the antenna as far as possible from sources of interference. The
drawback is that the module may be less convenient to use.
• Shield the host device. The module itself is well shielded to avoid external
interference. However, the antenna cannot be shielded for obvious reasons.
In most instances, it is necessary to employ shielding on the components of
the host device (such as the main processor and parallel bus) that have the
highest RF emissions.
• Filter out unwanted high-order harmonic energy by using discrete filtering on
low frequency lines.