u-blox SAM-M8Q Integration Manual

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u-blox SAM-M8Q Integration Manual Manual pdf 19 page image

SAM-M8Q - Hardware Integration ManualUBX-16018358 - R05 Production Information Product handlingPage 19 of 233.4 Applications with cellular modulesGSM terminals transmit power levels up to 2 W (+33 dBm) peak, 3G and LTE up to 250 mW continuous. Consultthe corresponding product data sheet in Related documents for the absolute maximum power input at theGNSS receiver.See the GPS Implementation and Aiding Features in u-blox wireless modules [7].Isolation between GNSS and cellular antennaIn a handheld type design, an isolation of approximately 20 dB can be reached with careful placement of theantennas. If such isolation cannot be achieved, e.g. in the case of an integrated cellular /GNSS antenna, anadditional 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 immunityInterference signals come from in-band and out-band frequency sources.In-band interferenceWith in-band interference, the signal frequency is very close to the GNSS constellation frequency used, e.g. GPSfrequency of 1575 MHz (see Figure 10 ). Such interference signals are typically caused by harmonics fromdisplays, micro-controller, bus systems, etc.1525 1550 1625GPS input filtercharacteristics1575 16000-110Jamming signal1525 1550 1625Frequency [MHz]Power [dBm]GPS input filtercharacteristics1575 16000JammingsignalGPSsignalsGPS Carrier1575.4 MHzFigure 10: In-band interference signalsFigure 11: In-band interference sources