RF Integration
Rev 2 Apr.12
Proprietary and Confidential
13
Determining the antenna’s location
When deciding where to put the antennas:
•
Antenna location may affect RF performance. Although the module is
shielded to prevent interference in most applications, the placement of the
antenna is still very important—if the host device is insufficiently shielded,
high levels of broadband or spurious noise can degrade the module’s perfor-
mance.
•
Connecting cables between the module and the antenna must have 50
impedance. If the impedance of the module is mismatched, RF performance
is reduced significantly.
•
Antenna cables should be routed, if possible, away from noise sources
(switching power supplies, LCD assemblies, etc.). If the cables are near the
noise sources, the noise may be coupled into the RF cable and into the
antenna.
Disabling the diversity antenna
•
Use the AT command
!RXDEN=0
to disable receive diversity or
!RXDEN=1
to
enable receive diversity.
Note: A diversity antenna is used to improve connection quality and reliability through
redundancy. Because two antennas may experience difference interference effects (signal
distortion, delay, etc.), when one antenna receives a degraded signal, the other may not be
similarly affected.
Interference and sensitivity
Several sources of interference can affect the RF performance of the module
(RF desense). Common sources include power supply noise and device-
generated RF.
RF desense can be addressed through a combination of mitigation techniques
(
Methods to mitigate decreased Rx performance
on page 13) and radiated
sensitivity measurement (
Radiated sensitivity measurement
on page 14).
Note: The EM7700 is based on ZIF (Zero Intermediate Frequency) technologies. When
performing EMC (Electromagnetic Compatibility) tests, there are no IF (Intermediate
Frequency) components from the module to consider.
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.
Summary of Contents for AirPrime EM7700
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