EVA-M8M - Hardware Integration Manual
UBX-14006179 - R02
Early Production Information
Design-in
Page 25 of 45
2.13.4
EOS protection measures
EOS protection measures as shown in Figure 7 are recommended for any designs combining wireless
communication transceivers (e.g. GSM, GPRS) and GNSS in the same design or in close proximity.
Passive antennas
Active Antennas
(without internal filter
which need the module antenna supervisor
circuits)
C
D
LNA with appropriate ESD rating
and maximum input power.
Figure 7: EOS and ESD Precautions
2.13.5
Applications with cellular modules
GSM uses power levels up to 2W (+33dBm). Make sure that absolute maximum input power level of the GNSS
receiver is not exceeded.
See the
GPS Implementation and Aiding Features in u-blox wireless modules
2.13.5.1
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 can’t 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.
2.13.5.2
Increasing interference immunity
Interference signals come from in-band and out-band frequency sources.
2.13.5.3
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
