EVA-M8M - Hardware Integration Manual
The EVA-M8M modules can receive and track multiple GNSS system (e.g. GPS/QZSS, GLONASS, and BeiDou
signals). Because of the dual-frequency RF front-end architecture, two of the three signals (GPS L1C/A, GLONASS
L1OF and BeiDou B1) can be received and processed concurrently.
2.5.1
Active Antenna
In case an active antenna is used, just the active antenna supply circuit has to be added in front of the EVA-M8M
modules RF-input, see Figure 16. In case the active antenna has to be supervised, either the 2-pin active antenna
supervisor circuit (see Figure 19) or the 3-pin active antenna supervisor circuit (see Figure 20), has to be added to
the active antenna circuit. These active antenna supervisor circuits also make sure that the active antenna is
turned off in Power Save Mode stages.
2.5.2
Passive Antenna
If a passive antenna is connected to the EVA-M8M modules, it is mandatory to use an additional LNA in front of
EVA-M8M to achieve the performance values as written in the
EVA-M8M Data Sheet
(U1) alone would make the EVA-M8M modules more sensitive to out-band jammers, so an additional GNSS
SAW filter (F1) has to be connected between the external LNA (U1) and the EVA-M8M RF-input If strong out-
band jammers are close to the GNSS antenna (e.g. a GSM antenna), see section 2.5.3.
The LNA (U1) can be selected to deliver the performance needed by the application in terms of:
•
Noise figure (sensitivity)
•
Selectivity and linearity (Robustness against jamming)
•
Robustness against RF power and ESD
The external LNA (U1) must be placed close to the passive antenna to get best performance.
The
ANT_OFF
pin can be used to turn off an external LNA. The
ANT_OFF
signal must be inverted for common
LNAs which come with an enable pin which has be “low” to turn off.
The the function of the
ANT_OFF
pin can be inverted by sending the following sequence to the receiver:
B5 62 06 41 0C 00 00 00 03 1F 90 47 4F B1 FF FF EA FF 33 98
Applying this sequence results in a permanent change and cannot be reversed.
A pull-down resistor (R7) is required to ensure correct operation of the
ANT_OFF
pin.
ESD discharge into the RF input cannot always be avoided during assembly and / or field use with this approach!
To provide additional robustness an ESD protection diode, as listed in Appendix B.7, can be placed in front of the
LNA to GND.
2.5.3
Improved Jamming Immunity
If strong out-band jammers are close to the GNSS antenna (e.g. a GSM antenna) GNSS performance can be
degraded or the maximum input power of the EVA-M8M series RF-input can be exceeded. An additional SAW
filter (F2) has to put in front of the external LNA (U1), see Appendix A. If the external LNA can accept the
maximum input power, the SAW filter between the passive antenna and external LNA (LNA1) might not be
necessary. This results in a better noise figure than an additional SAW filter (F2) in front of the external LNA (U1).
If the EVA-M8M modules are exposed to an interference environment, it is recommended to use additional
filtering. Improved interference immunity with good GNSS performance can be achieved when using a
SAW/LNA/SAW configuration between the antenna and the EVA-M8M RF-input. The single-ended SAW filter
(F2) can be placed in front of the LNA matching network to prevent receiver blocking due to strong interference,
see Figure 15.
It should be noted that the insertion loss of SAW filter (F2) directly affects the system noise figure and hence the
system performance. Choice of a component with low insertion loss is mandatory when a passive antenna is
used with this set-up. An example schematic for an improved jamming immunity is shown in Appendix A.3 (see
Figure 15).
UBX-14006179 - R01
Advance Information
Design-in
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