ZOE-M8B - System Integration Manual
UBX-17045131 - R04
Contents
Page 28 of 42
Production Information
http://www.murata.com/products/emc/knowhow/pdf/4to5e.pdf
Improved EMI protection can be achieved by inserting a resistor or better yet a ferrite bead or an
inductor (see Table 14) into any unshielded PCB lines connected to the GNSS receiver. Place the
resistor as close as possible to the GNSS receiver pin.
Alternatively, feed-thru capacitors with good GND connection can be used to protect e.g. the VCC
supply pin against EMI. A selection of feed-thru capacitors are listed in Table 14.
Intended use
☞
In order to mitigate any performance degradation of radio equipment under EMC disturbance,
system integration shall adopt appropriate EMC design practice and not contain cables over three
meters on signal and supply ports.
2.14.6
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
ZOE-M8B Data Sheet [1] for the absolute maximum power input at the GNSS
receiver. Make sure that absolute maximum input power level of the GNSS receiver is not exceeded.
☞
See the
GPS Implementation and Aiding Features in u-blox wireless modules [4].
2.14.6.1
Isolation between GNSS and GSM antenna
In a handheld type design, an isolation of approximately 20 dB can be reached with careful placement
of the antennas. If such isolation can’t be achieved, e.g. in the case of an integrated GSM/GNSS
antenna, an additional input filter is needed on the GNSS side to block the high energy emitted by the
GSM transmitter. Examples of these kinds of filters would be the SAW Filters from Epcos (B9444 or
B7839) or Murata.
2.14.6.2
Increasing interference immunity
Interference signals come from in-band and out-band frequency sources.
2.14.6.3
In-band interference
With in-band interference, the signal frequency is very close to the GPS frequency of 1575 MHz (see
Figure 21). 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
Interference
signal
GPS
signals
GPS Carrier
1575.4 MHz
Figure 21: In-band interference signals
