AirPrime EM7700 Hardware Integration Guide
14
Proprietary and Confidential
4112206
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:
•
CE/ETSI EN 301 908 (WCDMA), test numbers 5.3.1 (‘Radiated Emissions
(UE)’)
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.)
Radiated sensitivity measurement
A wireless host device contains many noise sources that contribute to a reduction
in Rx performance.
To determine the extent of any receiver performance desensitization due to self-
generated noise in the host device, over-the-air (OTA) or radiated testing is
required. This testing can be performed by Sierra Wireless or you can use your
own OTA test chamber for in-house testing.
Power supply noise
Noise in the power supply can lead to noise in the RF signal.
The power supply ripple limit for the module is no more than 100 mVp-p 1 Hz to
100 kHz. This limit includes voltage ripple due to transmitter burst activity.
Additional decoupling capacitors can be added to the main VCC line to filter noise
into the device.
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.
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