MAX-M10S - Integration manual
Figure 23: VCC and V_IO supplied by separate supplies, and external power supply at V_BCKP
Figure 24: VCC and V_IO supplied by separate supplies. No external power supply at V_BCKP.
3.2 RF interference
The received GNSS signal power at the antenna is very low compared to other wireless
communication signals. The nominal -130 dBm received GNSS signal strength is below the thermal
noise floor, making a GNSS receiver susceptible to interference from nearby RF sources of any kind.
As an example, cellular applications emit signals with power levels of approxi30 dBm, while
the GNSS signal is less than -128 dBm when reaching the antenna. By simply comparing these
numbers it is obvious that interference issues must be seriously considered during the design
phase.
3.2.1 In-band interference
Although the radio communications standards prevent intentional RF signal sources from
interfering the GNSS frequencies, many devices emit RF power into the GNSS band at levels much
higher than the GNSS signal itself.
One reason is that the frequency band above 1 GHz is not well regulated with regards to EMI,
and even if permitted, signal levels are much higher than the GNSS signal power. In particular,
all types of digital equipment, such as PCs, digital cameras, LCD screens, etc. tend to emit a
broad frequency spectrum up to several GHz of frequency. Also wireless transmitters may generate
spurious emissions that fall into the GNSS band.
The section
defines measures against in-band interference during the design phase
of the application.
3.2.2 Out-of-band interference
Out-of-band interference is caused by signal frequencies that are different from the GNSS carrier
frequency. The main sources are wireless communication systems such as LTE, GSM, CDMA,
WCDMA, Wi-Fi, BT, etc. Typically, these systems may emit their specified maximum transmit power
in close proximity to the GNSS receiving antenna, especially if such a system is integrated with
the GNSS receiver. Even at reasonable antenna selectivity, destructive power levels may reach the
RF input of the GNSS receiver. In addition, larger signal interferers may generate intermodulation
UBX-20053088 - R03
3 Hardware integration
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