UBX-G7020 - Hardware Integration Manual
Design-in
GPS.G7-HW-10003 Objective Specification Page 33 of 74
Different design goals may be achieved through different implementations:
1. The primary focus is prevention of destruction of the receiver from large input signals. Here the
GPS/GNSS performance under interference conditions is not important and suppression of the
GPS/GNSS signal is permitted. It is sufficient to just observe the maximum RF power ratings of all the
components in the RF input path.
2. GPS/GNSS performance must be guaranteed even under interference conditions. In that case, not only
the maximum power ratings of the components in the receive patch must be observed. Further, non-
linear effects like gain compression, NF degradation (desensitization) and intermodulation must be
analyzed.
Pulsed interference with a low duty cycle like e.g. GSM usually does not affect GPS/GNSS performance
but may be destructive due to the high peak power levels.
2.6.1.1 In-band interference mitigation
With in-band interference the signal frequency is very close to the GPS/GNSS frequency of 1575 MHz (see Figure
14). Such interference signals are typically caused by harmonics from displays, micro-controller operation, bus
systems, etc.
1525 1550 1625
GPS input filter
characteristics
1575 1600
0
-110
Jammin
g signal
1525 1550 1625
Frequency [MHz]
Power [dBm]
GPS input filter
characteristics
1575 1600
0
Interference
signal
GPS
signals
GPS Carrier
1575.4 MHz
Figure 14: In-band interference signals
u-blox GPS
receiver
CPU
data bus
Figure 15: In-band interference sources
Measures against in-band interference include:
Maintaining a good grounding concept in the design
Shielding
Layout optimisation
Low-pass filtering of noise sources, e.g. digital signal lines
Remote placement of the GPS/GNSS antenna, far away from noise sources
Adding a CDMA, GSM, WCDMA,BT band-pass filter before antenna
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