LEA-M8F - Hardware Integration Manual
UBX-14000034 - R03
Early Production
Information
Product
handling
Page 26 of 30
Example of EMI protection measures on the RX/TX line using a ferrite bead:
VCC
can be protected using a feed thru capacitor. For electromagnetic compatibility (EMC) of the RF_IN pin,
refer to section Soldering.
4.4
Applications with cellular modules
GSM uses power levels up to 2 W (+33 dBm). 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
Isolation between GNSS and GSM antenna
In a handheld type design, 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 GSM/GNSS antenna, an
additional input filter is needed on the GNSS side to block the high energy emitted by the GSM transmitter.
Examples of these kinds of filters would be the SAW Filters from Epcos (B9444 or B7839) or Murata.
Increasing jamming immunity
Jamming signals come from in-band and out-band frequency sources.
In-band jamming
With in-band jamming, the signal frequency is very close to the GNSS constellation frequency used, e.g. GPS
frequency of 1575 MHz (see
Figure 19). Such jamming 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 19: In-band jamming signals
TX
RX
G
N
SS
R
ec
ei
ver
FB
FB
BLM15HD102SN1
>10mm
Figure 18: EMI Precautions
