Device-Generated Rf - Sierra Wireless MC5725V Hardware Integration Manual

CDMA and GSM / UMTS Mini Card Hardware Integration Guide
Note: The module can cause
interference with other devices
such as hearing aids and on-
board speakers.
Wireless devices such as the
Mini Card 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.
Note: It is important to
investigate sources of localized
interference early in the design
cycle.
22
In the event of a discrepancy in values between this guide and the Product Specification Document (PSD), the PSD takes precedence.

Device-generated RF

All electronic computing devices generate RF interference that
can negatively affect the receive sensitivity of the module.
The proximity of host electronics to the antenna in wireless
devices can contribute to decreased Rx performance. Compo‐
nents that are most likely to cause this include:
• Microprocessor and memory
• Display panel and display drivers
• Switching‐mode power supplies
These and other high‐speed devices (in particular, the
processor) can decrease Rx performance because they run at
frequencies of tens of MHz. The rapid rise and fall of these
clock signals generates higher‐order harmonics that often fall
within the operating frequency band of the module, affecting
the module's receive sensitivity.
Example
On a sub‐system running at 40 MHz, the 22nd harmonic falls
at 880 MHz, which is within the cellular receive frequency
band.
Note: In practice, there are usually numerous interfering frequencies
and harmonics. The net effect can be a series of desensitized receive
channels.
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