u-blox NEO-M8P-2, Руководство по интеграции оборудования

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NEO-M8P - Hardware Integration Manual
UBX-15028081 - R05 Early Production Information
Product handling
Page 22 of 27
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 [5].
Isolation between GNSS and GSM antenna
In a handheld design, an antenna isolation of approximately 20 dB can be reached with careful placement of the
antennas. If this isolation factor cannot be achieved, e.g. in the case of an integrated GSM/GNSS antenna, an
additional input filter is required on the GNSS side to reduce the energy coupled from the GSM transmitter.
Examples of these filters are 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 13 ). Such interference signals are typically caused by harmonics emitted from
displays, micro-controller, data-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 13: In-band interference signals
Figure 14: In-band interference sources