MAX-7 / NEO-7 - Hardware Integration Manual
UBX-13003704
-
R09
Production Information
Product
handling
Page
45 of 52
VCC
can be protected using a feed thru capacitor. For electromagnetic compatibility (EMC) of the RF_IN pin,
refer to section 5.3.5
Intended use
In order to mitigate any performance degradation of a 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.
7.3.7
Applications with cellular modules
GSM uses power levels up to 2 W (+33 dBm). Consult the Data Sheet for the absolute maximum power input at
the GNSS receiver.
7.3.7.1
Isolation between GPS 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 cannot be achieved, e.g. in the case of an integrated GSM/GPS antenna, an additional
input filter is needed on the GPS 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.
7.3.7.2
Increasing jamming immunity
Jamming signals come from in-band and out-band frequency sources.
7.3.7.3
In-band jamming
With in-band jamming the signal frequency is very close to the GPS frequency of 1575 MHz (see
Figure 35). Such
jamming 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 35: In-band jamming signals
Figure 36: In-band jamming sources
Measures against in-band jamming include:
Maintaining a good grounding concept in the design
Shielding
