SAM-M8Q - Hardware Integration Manual
UBX-16018358 - R05
Production Information
Product handling
Page 19 of 23
3.4
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
[7].
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 10
). 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 10: In-band interference signals
Figure 11: In-band interference sources
