NEO-8Q / NEO-M8 - Hardware integration manual
UBX-15029985 - Production information Hardware description Page 10 of 11
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1.6 Electromagnetic interference on I/O lines
Any I/O signal line with a length greater than approximately 3 mm can act as an antenna and may pick
up arbitrary RF signals transferring them as noise into the GNSS receiver. This specifically applies to
unshielded lines, in which the corresponding GND layer is remote or missing entirely, and lines close
to the edges of the printed circuit board.
If, for example, a cellular signal radiates into an unshielded high-impedance line, it is possible to
generate noise in the order of volts and not only distort receiver operation but also damage it
permanently.
On the other hand, noise generated at the I/O pins will emit from unshielded I/O lines. Receiver
performance may be degraded when this noise is coupled into the GNSS antenna (see Figure 15).
To avoid interference by improperly shielded lines, it is recommended to use resistors (e.g. R>20 Ω),
ferrite beads (e.g. BLM15HD102SN1) or inductors (e.g. LQG15HS47NJ02) on the I/O lines in series.
These components should be chosen with care because they will also affect the signal rise times.
Figure 3 shows an example of EMI protection measures on the RXD/TXD line using a ferrite bead. For
more information, see section 4.3.
Figure 3: EMI precautions
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