Device-Generated Rf Interference; Methods To Mitigate Decreased Rx Performance; Radiated Spurious Emissions (Rse) - Sierra Wireless AirPrime EM7355 Hardware Integration Manual

Rev 1 Dec.12 Proprietary and Confidential - Contents subject to change
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.
• Form shielding layers around high-speed clock traces by using multi-layer
PCBs.
• Route antenna cables away from noise sources.

Radiated Spurious Emissions (RSE)

When designing an antenna for use with AirPrime embedded modules, the host
device with an AirPrime embedded module must satisfy the radiated spurious
emission (RSE) test cases described in:
• (CDMA) Refer to CDMA standards for receive-only mode, and local
regulatory bodies for transmit mode (transmitter is operating).
• CE/ETSI EN 301 908 (WCDMA), test numbers 5.3.1 ('Radiated Emissions
(UE)')
• CE/ETSI EN 301 511 (GSM), test 5.2.16 ('Radiated Spurious Emissions - MS
allocated a channel'). This test uses the procedure and requirement outlined
in 3GPP 51.010 (GSM) section 12.2.1 of the same test name.
Note that antenna impedance affects radiated emissions, which must be
compared against the conducted 50-ohm emissions baseline. (AirPrime
embedded modules meet the 50-ohm conducted emissions requirement.)
RF Specifications
15