LEA-M8S / LEA-M8T - Hardware Integration Manual
UBX-13003140 - R07
Production Information
Product handling
Page 26 of 31
4.4
Applications with cellular modules
GSM uses power levels up to 2 W (+33 dBm). Consult the
[1] and the
NEO/LEA-M8T
Data
Sheet
[2] 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 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 18). 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 18: In-band interference signals
Figure 19: In-band interference sources
