ZED-F9T - Integration Manual
If the amount of data configured is too much for a certain port's bandwidth (e.g. all UBX
messages output on a UART port with a baud rate of 9600), the buffer will fill up. Once the
buffer space is exceeded, new messages to be sent will be dropped.
Inbound data to the GNSS receiver are placed in buffers. Usage of these buffers can be monitored
through the UBX-MON-COMMS message. Further, as data are then parsed within the receiver (e.g.
to separate UBX and NMEA data), the UBX-MON-COMMS message can be used. This message
shows (for each port and protocol) how many messages were successfully received. It also shows (for
each port) how many bytes were discarded because they were not in any of the supported protocol
framings.
3.7.1.2 Jamming/interference indicator / cw jamming monitoring
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 value for the unjammed case. If the value rises significantly above this threshold, this
indicates that a continuous wave jammer is present.
This indicator is always enabled.
The indicator is reporting any currently detected narrow-band interference over all currently
configured signal bands.
3.7.1.3 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
above.
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 20: Jamming/interference monitor reported states
The monitor is disabled by default. The monitor is enabled by sending an appropriate CFG-ITFM-
* configuration group with the CFG-ITFM-ENABLE bit set. 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 passive antenna.
The monitor 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.
UBX-19005590 - R01
3 Receiver functionality
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