MIA-M10Q - Integration manual
number of filters are selected based on the estimated interference level and the immunity of the
receiver.
RF interference from other parts of the design is more difficult to estimate. One option is to measure
the interference level at the receiver input using a spectrum analyzer. Interference within the design
is primarily a problem at the receiver in-band, where it cannot be addressed by filtering on the RF
path. Outside the GNSS band, the required filtering is determined by the estimated interference
level and the immunity of the receiver.
3.4.4 Antenna power supply
An active antenna supply network to connect antenna supply to the RF signal line is shown in
. The inductance L3 connects the antenna power supply to the RF signal line. The capacitance
C14 filters out high-frequency interference from the power supply and the resistor R8 limits the
short-circuit current.
The type and value of L3 is selected to have a resonance peak at GNSS frequencies. This provides a
high series impedance above 500 Ω at GNSS L1 frequencies, creating an impedance mismatch with
respect to the 50 Ω RF signal line. This minimizes the effect of the feed point on the RF signal line,
and isolates the antenna supply from the RF signal line at GNSS frequencies. Both R8 and L3 must
have sufficient current and power rating to withstand the short-circuit current. Example component
values for the antenna supply network are given in
, and
.
The
can be used to detect open and short circuits on the antenna supply
network and disconnect the antenna supply if a short circuit is detected.
Figure 30: Antenna supply network
3.5 Layout
GNSS signals on the surface of the earth have a very low signal strength and are about 15 dB
below the thermal noise floor. When integrating a GNSS receiver into a PCB, the placement of the
components, as well as grounding, shielding, and interference from other digital devices are crucial
issues that need to be considered very carefully.
An important factor in achieving high GNSS performance is the placement of the receiver with
respect to other components on the PCB.
UBX-21028173 - R01
3 Hardware integration
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