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observed. Further, non-linear effects like gain compression, NF degradation (desensitization)
and intermodulation must be analyzed.
Pulsed interference with a low-duty cycle such as GSM may be destructive due to the high
peak power levels.
4.5.2 In-band interference mitigation
With in-band interference, the signal frequency is very close to the GNSS frequency. Such
interference signals are typically caused by harmonics from displays, micro-controller operation, bus
systems, etc. Measures against in-band interference include:
• Maintaining a good grounding concept in the design
• Shielding
• Layout optimization
• Low-pass filtering of noise sources, e.g. digital signal lines
• Remote placement of the GNSS antenna, far away from noise sources
• Adding an LTE, CDMA, GSM, WCDMA, BT band-pass filter before antenna
4.5.3 Out-of-band interference
Out-of-band interference is caused by signal frequencies that are different from the GNSS carrier
frequency. The main sources are wireless communication systems such as LTE, GSM, CDMA,
WCDMA, Wi-Fi, BT, etc.
Measures against out-of-band interference include maintaining a good grounding concept in the
design and adding a GNSS band-pass filter into the antenna input line to the receiver.
For GSM applications, such as typical handset design, an isolation of approximately 20 dB can be
reached with careful placement of the antennas. If this is insufficient, an additional SAW filter is
required on the GNSS receiver input to block the remaining GSM transmitter energy.
4.6 Thermal management
During design-in do not place the receiver near sources of heating or cooling. The receiver oscillator
is sensitive to sudden changes in ambient temperature which can adversely impact satellite signal
tracking. Sources can include co-located power devices, cooling fans or thermal conduction via the
PCB. Take into account the following questions when designing in the receiver.
• Is the receiver placed away from heat sources?
• Is the receiver placed away from air-cooling sources?
• Is the receiver shielded by a cover/case to prevent the effects of air currents and rapid
environmental temperature changes?
High temperature drift and air vents can affect the GNSS performance. For best
performance, avoid high temperature drift and air vents near the receiver.
UBX-22004121 - R01
C1-Public
4 Design
Early production information
RCB-F9T - Integration manual
Page 58 of 64
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