NEO-8Q / NEO-M8 - Hardware integration manual
UBX-15029985 - Production information
Product handling
Page 25 of 26
C1-Public
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 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, for example, 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 are 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, for example, GPS frequency of 1575 MHz (see Figure 14). Such interference signals are typically
caused by harmonics from displays, micro-controller, bus systems, and so on.
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
