Sierra Wireless AirPrime SL8080, Руководство по интеграции оборудования, Страница: 12 / 22

AirPrime SL8080 Series Hardware Integration Guide
12 Proprietary and Confidential 2400058
Antenna guidelines
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

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,
CE, etc.) test results.
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 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.
RF desense sources
Common sources of interference that may affect the module’s RF performance
(RF desense) include
• Power supply noise
· Can lead to noise in the RF signal
· Module power supply ripple limit <= 100 mV
p-p
1 Hz–100 kHz
• Interference from other embedded wireless devices
· Any harmonics, sub-harmonics, or cross-products of signals that fall in the
module’s Rx range may cause spurious response, resulting in decreased
Rx performanc.
· Tx power and corresponding broadband noise may overload or increase
the noise floor of the module’s receiver, resulting in RF desense.
· Severity of interference depends on proximity of other antennas to the
module’s antenna.s
• Host electronic device-generated RF
· Proximity of host electronics to the module’s antenna can contribute to
decreased Rx performance.
· Some devices include microprocessor and memory, display panel and
dispaly drivers, and switching mode power supplies.