u-blox NEO-8Q Series - Applications with Cellular Modules

NEO-8Q / NEO-M8 - Hardware Integration Manual
UBX-15029985 - R04 Production Information Product handling
Page 26 of 31
4.4 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 corresponding product data sheet in Related documents for the absolute maximum power input at the GNSS
receiver.
See the GPS Implementation and Aiding Features in u-blox wireless modules [8].
Isolation between GNSS and cellular 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 cellular /GNSS 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 sources