MAX-7 / NEO-7 / LEA-7 - Hardware Integration Manual
GPS.G7-HW-11006-1
Product handling
Page 49 of 55
5.3.7
Applications with wireless modules LEON / LISA
GSM uses power levels up to 2 W (+33 dBm). Consult the Data Sheet for the absolute maximum power input at
the GPS/GNSS receiver.
5.3.7.1
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.
5.3.7.2
Increasing jamming immunity
Jamming signals come from in-band and out-band frequency sources.
5.3.7.3
In-band jamming
With in-band jamming the signal frequency is very close to the GPS frequency of 1575 MHz (see
). 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 38: In-band jamming signals
Figure 39: In-band jamming sources
Measures against in-band jamming include:
•
Maintaining a good grounding concept in the design
•
Shielding
•
Layout optimization
•
Filtering
•
Placement of the GPS antenna
•
Adding a CDMA, GSM, WCDMA band pass filter before handset antenna
