NEO-M8U - Hardware Integration Manual
UBX-15016700 - R07
Product handling
Page 23 of 28
Production Information
5.4
Applications with cellular modules
GSM terminals transmit power levels up to 2 W (+33 dBm) peak, 3G and LTE up to 250 mW
continuous. Consult the Data Sheet for the absolute maximum power input at the GNSS receiver.
☞
See the GPS Implementation and Aiding Features in u-blox wireless modules [6].
Isolation between GNSS and cellular antennas
In multi-antenna designs, an isolation of approximately 20 dB can be reached with careful placement
of the antennas. If such isolation cannot be achieved, e.g. in the case of an integrated cellular antenna,
an additional input filter is needed on the GNSS side to block the high energy emitted by the cellular
transmitter. Examples of these kinds of filters would be the SAW Filters from Epcos (B9444 or B7839)
or Murata.
Increasing interference immunity
Interference signals come from in-band and out-band frequency sources.
In-band interference
With in-band interference, the signal frequency is very close to the GNSS constellation frequency
used, e.g. GPS frequency of 1575 MHz (see
Figure 14). 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
Jamming
signal
GPS
signals
GPS Carrier
1575.4 MHz
Figure 14: In-band interference signals
Figure 15: In-band interference sourcesMeasures against in-band interference include:
•
Maintaining a good grounding concept in the design
•
Shielding
•
Layout optimization
•
Filtering
•
Placement of the GNSS antenna
•
Adding a CDMA, GSM, WCDMA band pass filter before handset antenna
