Sierra Wireless AirPrime MC7350, Руководство по интеграции оборудования

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4114814 Rev 1.1 November 19, 2013 11
Hardware Integration Guide RF Integration
3.3. Shielding Guidelines
The mini card is fully shielded to protect against EMI and to ensure compliance with FCC Part 15 -
“Radio Frequency Devices” (or equivalent regulations in other jurisdictions).
Note: The module shields must NOT be removed.
3.4. Antenna Guidelines
When selecting the antenna and cable, it is critical to RF performance to match antenna gain and
cable loss.
3.4.1. Choosing the Correct Antenna and Cabling
Consider the following points for appropriate antenna selection:

The antenna (and associated circuitry) should have a nominal impedance of 50
Ω
with a return
loss of better than 10 dB across each frequency band of operation.

The system gain value affects both radiated power and regulatory (FCC, IC, etc.) test results.
3.4.2. Designing Custom Antennas
Note that in designing custom antennas, a skilled RF engineer should do the development to ensure
that the RF performance is maintained.
3.4.3.
Determining the Antenna’s Location
Consider the following points when deciding where to place the antenna:

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 performance.

Connecting cables between the module and the antenna must have 50
Ω
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.
3.4.4. Disabling the Diversity Antenna

For LTE bands, use the AT command
!RXDEN=0
to disable receive diversity or
!RXDEN=1
to
enable receive diversity.

For CDMA bands, use the AT command
!DIVERSITY
to enable or disable 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.