RCB-F9T - Integration manual
algorithms rely on availability of signals from multiple GNSS constellations; the detection does not
work in single-GNSS mode.
3.9.2 Jamming/interference indicator
The field
jamInd
of the UBX-MON-RF message can be used as an indicator for continuous
wave (narrow-band) jammers/interference only. The interpretation of the value depends on the
application. It is necessary to run the receiver in an unjammed environment to determine an
appropriate threshold for the unjammed case. If the value rises significantly above this threshold,
this indicates that a continuous wave jammer is present.
This monitoring function is always enabled.
The indicator reports any currently detected narrow-band interference over all currently configured
signal bands.
3.9.2.1 Jamming/interference monitor (ITFM) / broadband interference monitoring
The field
flags
of the UBX-MON-RF message can be used as an indicator for both broadband and
continuous wave (CW) jammers/interference. It is independent of the (CW only) jamming indicator
described in
Jamming/interference indicator
This monitor reports whether jamming has been detected or suspected by the receiver. The receiver
monitors the background noise and looks for significant changes. Normally, with no interference
detected, it will report "OK". If the receiver detects that the noise has risen above a preset threshold,
the receiver reports "Warning". If in addition, there is no current valid fix, the receiver reports
"Critical".
The monitor has four states as shown in the following table:
Value
Reported state
Description
0
Unknown
Jamming/interference monitor not enabled,
uninitialized or antenna disconnected
1
OK
no interference detected
2
Warning
position OK but interference is visible (above the
thresholds)
3
Critical
no reliable position fix and interference is visible (above
the thresholds); interference is probable reason why
there is no fix
Table 12: Jamming/interference monitor reported states
The monitor is disabled by default. The monitor is enabled by setting the CFG-ITFM-ENABLE
configuration item. In this message it is also possible to specify the thresholds at which broadband
and CW jamming are reported. These thresholds should be interpreted as the dB level above
"normal". It is also possible to specify whether the receiver expects an active or a passive antenna.
The monitoring algorithm relies on comparing the currently measured spectrum with a
reference from when a good fix was obtained. Thus the monitor will only function when the
receiver has had at least one (good) first fix, and will report "Unknown" before this time.
The monitor is reporting any currently detected interference over all currently configured signal
bands.
3.9.3 GNSS receiver integrity
UBX-19003747 - R04
3 Receiver functionality
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Early production information
