EVA-M8E - Hardware Integration Manual
UBX-15028542 - R05
Contents
Page 16 of 44
Production Information
2.5
RF input
The RF-input is already matched to 50 Ohms and has an internal DC block. To achieve the
performance values as written in the EVA-M8E Data Sheet [1], an active antenna with a good LNA
inside or the recommended LNA with passive antenna in front of EVA-M8E (must have a noise figure
below 1 dB).
The EVA-M8E module can receive and track different GNSS (GPS, GLONASS, GALILEO and BeiDou)
simultaneously. This concurrent operation is extended to 3 GNSS when both of GPS and GALILEO are
used in addition to GLONASS or Beidou.
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
RF-input, see Figure 17. In case the active antenna has to be supervised, either the 2-pin active
antenna supervisor circuit (see Figure 20) or the 3-pin active antenna supervisor circuit (see Figure
21), 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-M8E module, it is recommended to use an additional
LNA in front of EVA-M8E. An LNA (U1) alone would make the EVA-M8E module 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-M8E module’s 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, but
care should be taken to isolate its output from the antenna element to avoid signal distortion or
instability.
If Power Save Mode is used and the minimum current consumption has to be achieved, then the
external LNA should also be turned off. 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. An unstable supply
voltage at the VCC_IO pin while applying this sequence can also damage the receiver.
☞
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.
