EVA-8M and EVA-M8 series - Hardware Integration Manual
UBX-16010593 - R06
Design-in
Page 28 of 47
Early Production Information
2.13.6.3
In-band interference
With in-band interference, the signal frequency is very close to the GPS frequency of 1575 MHz (see
Figure 8). Such interference signals are typically caused by harmonics from displays, micro-controller,
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 8: In-band interference signals
Figure 9: In-band interference sources
Measures against in-band interference include:
•
Maintaining a good grounding concept in the design
•
Shielding
•
Layout optimization
•
Filtering e.g. resistors and ferrite beads
•
Placement of the GNSS antenna
•
Adding a CDMA, GSM, WCDMA bandbass filter before handset antenna
2.13.6.4
Out-band interference
Out-band interference is caused by signal frequencies that are different from the GNSS carrier (see
Figure 10). The main sources are wireless communication systems such as GSM, CDMA, WCDMA,
WiFi, BT, etc.
