Ublox RCB-F9T Use and care manual


RCB-F9T
u-blox RCB-F9T high accuracy timing board
Integration manual
Abstract
This document describes the features and application of RCB-F9T, a multi-
band GNSS timing board offering nanosecond-level timing accuracy.
www.u-blox.com
UBX-22004121 - R01
C1-Public

RCB-F9T-Integration manual
Document information
Title RCB-F9T
Subtitle u-blox RCB-F9T high accuracy timing board
Document type Integration manual
Document number UBX-22004121
Revision and date R01 28-Mar-2022
Document status Early production information
Disclosure restriction C1-Public
This document applies to the following products:
Type number FW version PCN reference RN reference
RCB-F9T-0-02 TIM 2.20 UBX-22003600 UBX-21050656
RCB-F9T-1-01 TIM 2.20 - UBX-21050656
u-blox or third parties may hold intellectual property rights in the products, names, logos and designs included in this
document. Copying, reproduction, modification or disclosure to third parties of this document or any part thereof is only
permitted with the express written permission of u-blox.
The information contained herein is provided "as is" and u-blox assumes no liability for its use. No warranty, either express
or implied, is given, including but not limited to, with respect to the accuracy, correctness, reliability and fitness for a
particular purpose of the information. This document may be revised by u-blox at any time without notice. For the most recent
documents, visit www.u-blox.com.
Copyright © 2022, u-blox AG.
UBX-22004121 - R01

Page 2 of 64
C1-Public Early production information

RCB-F9T-Integration manual
Contents
1 Integration manual overview............................................................................................. 5
2 System description...............................................................................................................6
2.1 Overview.................................................................................................................................................... 6
2.1.1 Differential timing.......................................................................................................................... 6
2.2 Architecture..............................................................................................................................................6
2.2.1 Block diagram..................................................................................................................................6
3 Receiver functionality.......................................................................................................... 7
3.1 Receiver configuration........................................................................................................................... 7
3.1.1 Changing the receiver configuration..........................................................................................7
3.1.2 Default GNSS configuration.........................................................................................................7
3.1.3 Default interface settings............................................................................................................ 8
3.1.4 Basic receiver configuration.........................................................................................................8
3.1.5 Differential timing mode configuration..................................................................................... 9
3.1.6 Primary and secondary output................................................................................................. 12
3.1.7 Legacy configuration interface compatibility........................................................................ 14
3.1.8 Navigation configuration............................................................................................................15
3.2 SBAS........................................................................................................................................................19
3.3 Geofencing..............................................................................................................................................21
3.3.1 Introduction................................................................................................................................... 21
3.3.2 Interface......................................................................................................................................... 21
3.3.3 Geofence state evaluation......................................................................................................... 21
3.4 Logging....................................................................................................................................................22
3.4.1 Introduction................................................................................................................................... 22
3.4.2 Setting the logging system up................................................................................................. 22
3.4.3 Information about the log.......................................................................................................... 23
3.4.4 Recording....................................................................................................................................... 23
3.4.5 Retrieval......................................................................................................................................... 25
3.4.6 Command message acknowledgment....................................................................................25
3.5 Communication Interface................................................................................................................... 26
3.5.1 UART............................................................................................................................................... 26
3.6 Predefined PIOs.....................................................................................................................................26
3.6.1 RESET_N........................................................................................................................................ 26
3.6.2 TIMEPULSE................................................................................................................................... 26
3.7 Antenna supervisor.............................................................................................................................. 27
3.7.1 Antenna supply control - ANT_OFF......................................................................................... 27
3.7.2 Antenna short detection - ANT_SHORT_N............................................................................ 27
3.7.3 Antenna short detection auto recovery.................................................................................. 28
3.7.4 Antenna open circuit detection - ANT_DETECT................................................................... 28
3.8 Multiple GNSS assistance (MGA)..................................................................................................... 29
3.8.1 Authorization................................................................................................................................ 29
3.8.2 Preserving MGA and operational data during power-off..................................................... 29
3.9 Clocks and time.....................................................................................................................................30
3.9.1 Receiver local time.......................................................................................................................30
3.9.2 Navigation epochs....................................................................................................................... 30
UBX-22004121 - R01

Contents Page 3 of 64
C1-Public Early production information

3.9.3 iTOW timestamps........................................................................................................................31
3.9.4 GNSS times...................................................................................................................................31
3.9.5 Time validity.................................................................................................................................. 31
3.9.6 UTC representation..................................................................................................................... 32
3.9.7 Leap seconds................................................................................................................................ 33
3.9.8 Real-time clock............................................................................................................................. 33
3.9.9 Date.................................................................................................................................................33
3.10 Timing functionality...........................................................................................................................34
3.10.1 Time pulse...................................................................................................................................34
3.11 Security.................................................................................................................................................38
3.11.1 Spoofing detection / monitoring............................................................................................ 38
3.11.2 Jamming/interference detection / monitoring....................................................................38
3.11.3 Consolidated signal security information............................................................................ 39
3.11.4 GNSS receiver integrity............................................................................................................39
3.12 u-blox protocol feature descriptions.............................................................................................. 40
3.12.1 Broadcast navigation data...................................................................................................... 40
3.12.2 Save-on-shutdown feature......................................................................................................49
3.12.3 Spectrum analyzer.................................................................................................................... 49
3.12.4 Sky view signal masking.......................................................................................................... 50
3.13 Forcing a receiver reset.....................................................................................................................51
3.14 Firmware upload................................................................................................................................. 52
4 Design..................................................................................................................................... 53
4.1 Pin assignment......................................................................................................................................53
4.2 Power supply..........................................................................................................................................53
4.2.1 VCC: Main supply voltage.......................................................................................................... 53
4.2.2 RCB-F9T VCC_ANT: Antenna power supply.......................................................................... 54
4.3 Antenna...................................................................................................................................................54
4.4 EOS/ESD precautions.......................................................................................................................... 55
4.4.1 ESD protection measures.......................................................................................................... 56
4.4.2 EOS precautions...........................................................................................................................56
4.4.3 Safety precautions...................................................................................................................... 56
4.5 Electromagnetic interference on I/O lines.......................................................................................57
4.5.1 General notes on interference issues......................................................................................57
4.5.2 In-band interference mitigation................................................................................................58
4.5.3 Out-of-band interference........................................................................................................... 58
4.6 Thermal management......................................................................................................................... 58
5 Product handling................................................................................................................. 59
5.1 ESD handling precautions.................................................................................................................. 59
Appendix.................................................................................................................................... 60
A RCB-F9T default configurations...........................................................................................................60
B Glossary......................................................................................................................................................60
C RCB-F9T PCB dimensions......................................................................................................................61
Related documents................................................................................................................ 62
Revision history.......................................................................................................................63

RCB-F9T-Integration manual
1 Integration manual overview
This document is an important source of information on all aspects of RCB-F9T system, software
and hardware design. The purpose of this document is to provide guidelines for a successful
integration of the receiver with the customer's end product.
UBX-22004121 - R01

1 Integration manual overview Page 5 of 64
C1-Public Early production information

RCB-F9T-Integration manual
2 System description
2.1 Overview
The RCB-F9T timing board enables multi-band GNSS timing in a compact form factor using the
ZED-F9T, the u-blox F9 high accuracy timing module. The ZED-F9T module provides nanosecond-
level timing accuracy in both standalone and differential timing modes.
In addition to the ZED-F9T module, the RCB-F9T timing board contains an SMB antenna connector
and 5 V power supply circuitry for an external active multi-band GNSS antenna. The 8-pin, 2.0 mm
pitch pin-header provides powering of the board, UART communications, and two independently
configurable time pulse signals.
2.1.1 Differential timing
The u-blox RCB-F9T high accuracy timing board takes local timing accuracy to the next level with
its differential timing mode.
In differential timing mode correction data is exchanged with other neighboring RCB-F9T timing
receivers via a communication network. In differential timing mode the RCB-F9T can operate either
as a master reference station, or as a slave station.
When RCB-F9T acts as a master reference timing station, it sends RTCM 3.3 differential corrections
to slave receivers.
When RCB-F9T acts as a slave receiver, it receives differential corrections RTCM 3.3 messages and
aligns its time pulse to the master reference station.
2.2 Architecture
The RCB-F9T timing board provides all the necessary RF and baseband processing to enable multi-
band GNSS timing. The block diagram below (Figure 1) shows the key functionality implemented in
the RCB-F9T.
2.2.1 Block diagram
Figure 1: RCB-F9T block diagram
An active antenna is mandatory with the RCB-F9T.
UBX-22004121 - R01

2 System description Page 6 of 64
C1-Public Early production information

RCB-F9T-Integration manual
3 Receiver functionality
This section describes the RCB-F9T operational features and their configuration.
3.1 Receiver configuration
The RCB-F9T is fully configurable with UBX configuration interface keys. The configuration
database in the receiver's RAM holds the current configuration, which is used by the receiver
at run-time. It is constructed on start-up of the receiver from several sources of configuration.
The configuration interface and the available keys are described fully in the applicable interface
description [2].
CAUTION The configuration interface has changed from earlier u-blox positioning receivers.
Legacy messages are deprecated, and will not be supported in future firmware releases.
Users are advised to adopt the configuration interface described in this document. See
legacy UBX-CFG message fields reference section in the applicable interface description [2].
Configuration interface settings are held in a database consisting of separate configuration items.
An item is made up of a pair consisting of a key ID and a value. Related items are grouped together
and identified under a common group name: CFG-GROUP-*; a convention used in u-center and
within this document. Within u-center, a configuration group is identified as "Group name" and the
configuration item is identified as the "item name" under the "Generation 9 Configuration View" -
"Advanced Configuration" view.
The UBX messages available to change or poll the configurations are UBX-CFG-VALSET, UBX-CFG-
VALGET, and UBX-CFG-VALDEL. For more information about these messages and the configuration
keys, see the configuration interface section in the applicable interface description [2].
3.1.1 Changing the receiver configuration
All configuration messages, including legacy UBX-CFG messages, will result in a UBX-ACK-ACK
or UBX-ACK-NAK response. If several configuration messages are sent without waiting for this
response then the receiver may pause processing of input messages until processing of a previous
configuration message has been completed. When this happens a warning message "wait for cfg
ACK" will be sent to the host.
3.1.2 Default GNSS configuration
The RCB-F9T default GNSS configuration is set as follows:
RCB-F9T-0:
• GPS: L1C/A, L2C
• GLONASS: L1OF, L2OF
• Galileo: E1B/C, E5b
• BeiDou: B1I, B2I
• QZSS: L1C/A, L2C
RCB-F9T-1:
• GPS: L1C/A
• GLONASS: L1OF
• Galileo: E1B/C, E5a
• BeiDou: B1I, B2a
• QZSS: L1C/A, L5
UBX-22004121 - R01

3 Receiver functionality Page 7 of 64
C1-Public Early production information

RCB-F9T-Integration manual
The NavIC L5 signal is supported by the RCB-F9T-1, but not enabled in the default GNSS
configuration. SBAS is also supported but not enabled by default as it is not recommended for timing
applications.
For more information about the default configuration, see the applicable interface description [2].
3.1.3 Default interface settings
Interface Settings
UART Output 115200 baud, 8 bits, no parity bit, 1 stop bit. NMEA GGA, GLL, GSA, GSV, RMC, VTG, TXT (and
no UBX) messages are output by default.
UART Input 115200 baud, 8 bits, no parity bit, 1 stop bit. UBX, NMEA and RTCM 3.3 messages are enabled
by default.
Table 1: Default configurations
Refer to the applicable interface description [2] for information about further settings.
By default the RCB-F9T outputs NMEA messages that include satellite data for all GNSS bands
being received. This results in a higher-than-before NMEA load output for each navigation period.
Make sure the UART baud rate being used is sufficient for the selected navigation rate and the
number of GNSS signals being received.
3.1.4 Basic receiver configuration
This section summarizes the basic receiver configuration most commonly used.
3.1.4.1 Communication interface configuration
Several configuration groups allow operation mode configuration of the various communication
interfaces. These include parameters for the data framing, transfer rate and enabled input/output
protocols. The configuration groups available for each interface are:
Interface Configuration groups
UART1 CFG-UART1-*, CFG-UART1INPROT-*, CFG-UART1OUTPROT-*
Table 2: Interface configurations
3.1.4.2 Message output configuration
The rate of the supported output messages is configurable.
If the rate configuration value is zero, then the corresponding message will not be output. Values
greater than zero indicate how often the message is output.
For periodic output messages the rate relates to the event the message is related to. For example,
the UBX-NAV-PVT (navigation, position, velocity and time solution) is related to the navigation
epoch. If the rate of this message is set to one (1), it will be output for every navigation epoch. If the
rate is set to two (2), it will be output every other navigation epoch. The rates of the output messages
are individually configurable per communication interface. See the CFG-MSGOUT-* configuration
group.
Some messages, such as UBX-MON-VER, are non-periodic and will only be output as an answer to
a poll request.
The UBX-INF-* and NMEA-Standard-TXT information messages are non-periodic output messages
that do not have a message rate configuration. Instead they can be enabled for each communication
interface via the CFG-INFMSG-* configuration group.
UBX-22004121 - R01

3 Receiver functionality Page 8 of 64
C1-Public Early production information

RCB-F9T-Integration manual
All message output is additionally subject to the protocol configuration of the
communication interfaces. Messages of a given protocol will not be output until the protocol
is enabled for output on the interface (see Communication interface configuration).
3.1.4.3 GNSS signal configuration
The GNSS constellations and signal bands are selected using keys from configuration group CFG-
SIGNAL-*. Each GNSS constellation can be enabled or disabled independently except for QZSS and
SBAS which are dependant on GPS selection. A GNSS constellation is considered to be enabled when
the constellation enable key is set and at least one of the constellation's band keys is enabled.
3.1.4.4 NMEA high precision mode
RCB-F9T supports NMEA high precision mode. This mode increases the reported precision of the
position output; latitude and longitude will have seven digits after the decimal point, and altitude
will have three digits after the decimal point. By default it is not enabled since it violates the NMEA
standard. NMEA high precision mode cannot be used while in NMEA compatibility mode or when
NMEA output is limited to 82 characters. See configuration item CFG-NMEA-HIGHPREC in the
applicable interface description [2] for more details.
NMEA high precision mode is disabled by default meaning that the default NMEA output
will be insufficient to report a high precision position.
3.1.5 Differential timing mode configuration
In differential timing mode the RCB-F9T can operate either as a master reference station or as a
slave station. Using the RTCM3 protocol, the master sends timing corrections to the slave via a
communication link enabling the slave to compute its time relative to the master with high accuracy.
This section describes how to configure the RCB-F9T high accuracy timing board as a master
reference station and as slave station. The section begins with a note describing the RTCM protocol
and corresponding supported message types.
3.1.5.1 RTCM corrections
RTCM is a binary data protocol for communication of GNSS correction information. The RCB-F9T
high accuracy timing board supports RTCM as specified by RTCM 10403.3, Differential GNSS
(Global Navigation Satellite Systems) Services – Version 3 (October 7, 2016).
The RTCM specification is currently at version 3.3 and RTCM version 2 messages are not supported
by this standard.
To modify the RTCM input/output settings, see the configuration section in the applicable interface
description [2].
3.1.5.2 List of supported RTCM input messages
Message type Description
RTCM 1005 Stationary RTK reference station ARP
RTCM 1077 GPS MSM7
RTCM 1087 GLONASS MSM7
RTCM 1097 Galileo MSM7
RTCM 1127 BeiDou MSM7
RTCM 1230 GLONASS code-phase biases
RTCM 4072.1 Additional reference station information (u-blox proprietary RTCM Message)
Table 3: RCB-F9T supported input RTCM version 3.3 messages
UBX-22004121 - R01

3 Receiver functionality Page 9 of 64
C1-Public Early production information

RCB-F9T-Integration manual
3.1.5.3 List of supported RTCM output messages
Message type Description
RTCM 1005 Stationary RTK reference station ARP
RTCM 1077 GPS MSM7
RTCM 1087 GLONASS MSM7
RTCM 1097 Galileo MSM7
RTCM 1127 BeiDou MSM7
RTCM 1230 GLONASS code-phase biases
RTCM 4072.1 Additional reference station information (u-blox proprietary RTCM Message)
Table 4: RCB-F9T supported output RTCM version 3.3 messages
3.1.5.4 Timing receiver position
Time mode is a special receiver mode where the position of the receiver is known and fixed and only
the time and frequency is calculated using all available satellites. This mode allows for maximum
time accuracy, for single-SV solutions, and also for using the receiver as a stationary reference
station.
In order to use time mode, the receiver's position must be known as exactly as possible. Errors in the
fixed position will translate into time errors depending on the satellite constellation.
The following procedures can be used to initialize the timing receiver position:
• Using built-in survey-in procedure to estimate the position.
• Entering coordinates independently generated or taken from an accurate position such as a
survey marker.
3.1.5.4.1 Survey-in
Survey-in is a procedure that is carried out prior to entering Time mode. It estimates the receiver
position by building a weighted mean of all valid 3D position solutions.
Two major parameters are required when configuring:
• A minimum observation time defines the minimum observation time independent of the
actual number of fixes used for the position estimate. Values can range from one day for high
accuracy requirements to a few minutes for coarse position determination.
• A 3D position standard deviation defines a limit on the spread of positions that contribute to
the calculated mean.
Survey-in ends when both requirements are successfully met. The Survey-in status can be queried
using the UBX-TIM-SVIN message.
To configure a timing receiver into Survey-in mode (CFG-TMODE-MODE=SURVEY_IN), the following
items are required:
Configuration item Description
CFG-TMODE-MODE Receiver mode (disabled, survey-in or fixed)
CFG-TMODE-SVIN_MIN_DUR Survey-in minimum duration
CFG-TMODE-SVIN_ACC_LIMIT Survey-in position accuracy limit. The accuracy of given coordinates in 0.0001
meters (i.e. value 100 equals 1 cm)
Table 5: Configuration items used for setting a timing receiver into Survey-in mode
Set the configuration items shown above into flash memory to perform a survey-in
procedure automatically upon start-up.
UBX-22004121 - R01

3 Receiver functionality Page 10 of 64
C1-Public Early production information

RCB-F9T-Integration manual
3.1.5.4.2 Fixed position
Here the timing receiver position coordinates are entered manually. Any error in the timing receiver
position will directly translate into timing errors.
To configure into Fixed mode (CFG-TMODE-MODE=FIXED), the following items are relevant:
Configuration item Description
CFG-TMODE-MODE Receiver mode (disabled or survey-in or fixed)
CFG-TMODE-POS_TYPE Determines whether the ARP position is given in ECEF or LAT/LON/HEIGHT
CFG-TMODE-ECEF_X ECEF X coordinate of the ARP position, coordinate in centimeters
CFG-TMODE-ECEF_Y ECEF Y coordinate of the ARP position, coordinate in centimeters
CFG-TMODE-ECEF_Z ECEF Z coordinate of the ARP position, coordinate in centimeters
CFG-TMODE-LAT Latitude of the ARP position, coordinate in 1e-7 degrees
CFG-TMODE-LON Longitude of the ARP position, coordinate in 1e-7 degrees
CFG-TMODE-HEIGHT Height of the ARP position, coordinate in centimeters
CFG-TMODE-ECEF_X_HP High-precision ECEF X coordinate of the ARP position, coordinate in 0.1 millimeters
CFG-TMODE-ECEF_Y_HP High-precision ECEF Y coordinate of the ARP position, coordinate in 0.1 millimeters
CFG-TMODE-ECEF_Z_HP High-precision ECEF Z coordinate of the ARP position, coordinate in 0.1 millimeters
CFG-TMODE-LAT_HP High-precision latitude of the ARP position, coordinate in 1e-9 degrees
CFG-TMODE-LON_HP High-precision longitude of the ARP position, coordinate in 1e-9 degrees
CFG-TMODE-HEIGHT_HP High-precision height of the ARP position, coordinate in 0.1 millimeters
CFG-TMODE-FIXED_POS_ACC Fixed position 3D accuracy estimate
Table 6: Configuration items used for setting a timing receiver into fixed mode
Once the receiver is set in fixed mode, select the position format to use: either LLH or ECEF with
optional high precision (mm) coordinates compared to the standard cm value.
For example, with CFG-TMODE-POS_TYPE=ECEF the timing receiver antenna position can be
entered to cm precision using CFG-TMODE-ECEF_X, CFG-TMODE-ECEF_Y, CFGTMODE-ECEF_Z.
For high precision (mm) coordinates use CFG-TMODEECEF_X_HP, CFG-TMODE-ECEF_Y_HP, CFG-
TMODE-ECEF_Z_HP. The same applies with corresponding coordinates used with CFG-TMODE-
POS_TYPE=LLH.
If the timing receiver is moved during operation then new position coordinates must be
configured.
3.1.5.5 Master reference station
When the RCB-F9T high accuracy timing board acts as a master timing station, it sends RTCM 3.3
differential corrections to slave receivers. Corrections are generated after a timing fix calculation in
order to remove the master receiver's clock offset.
3.1.5.5.1 Master reference station: RTCM output configuration
At this point the timing receiver should report a TIME fix, not a 3D fix.
The desired RTCM messages must be selected and configured on UART1 rate 1:
• RTCM 1005 Stationary RTK reference station ARP
• RTCM 1077 GPS MSM7
• RTCM 1088 GLONASS MSM7
• RTCM 1097 Galileo MSM7
• RTCM 1127 BeiDou MSM7
• RTCM 1230 GLONASS code-phase biases
• RTCM 4072.1 Additional reference station information
UBX-22004121 - R01

3 Receiver functionality Page 11 of 64
C1-Public Early production information

RCB-F9T-Integration manual
The configuration messages for these are shown in the Table 7.
The following configuration items output the recommended messages for a default satellite
constellation setting. Note that these are given for the UART1 interface:
Configuration item Description
CFG-UART1OUTPROT-NMEA CFG-UART1OUTPROT-NMEA to 0
CFG-UART1OUTPROT-RTCM3X CFG-UART1OUTPROT-RTCM3X to 1
CFG-UART1OUTPROT-UBX CFG-UART1OUTPROT-UBX to 0
CFG-MSGOUT-
RTCM_3X_TYPE1005_UART1
Output rate of the RTCM-3X-TYPE1005 message on port UART1: RTCM base
station message
CFG-MSGOUT-
RTCM_3X_TYPE1077_UART1
Output rate of the RTCM-3X-TYPE1077 message on port UART1: RTCM GPS
MSM7
CFG-MSGOUT-
RTCM_3X_TYPE1087_UART1
Output rate of the RTCM-3X-TYPE1087 message on port UART1: RTCM GLONASS
MSM7
CFG-MSGOUT-
RTCM_3X_TYPE1097_UART1
Output rate of the RTCM-3X-TYPE1097 message on port UART1: RTCM Galileo
MSM7
CFG-MSGOUT-
RTCM_3X_TYPE1127_UART1
Output rate of the RTCM-3X-TYPE1127 message on port UART1: RTCM Additional
reference station information
CFG-MSGOUT-
RTCM_3X_TYPE1230_UART1
Output rate of the RTCM-3X-TYPE1230 message on port UART1: RTCM GLONASS
code-phase biases
CFG-MSGOUT-
RTCM_3X_TYPE4072_1_UART1
Output rate of the RTCM-3X-TYPE4072.1 message on port UART1: RTCM
Additional reference station information
Table 7: Configuration items used for setting a master reference station
3.1.5.6 Slave station
When the RCB-F9T acts as a slave receiver, it receives differential corrections RTCM 3.3 messages
from a master reference station and aligns its time pulse to it.
Connect the slave receiver to the reference server or to the NTRIP server. When the slave receives
the configured RTCM correction stream, it will automatically start using the corrections.
Reception of RTCM 4072.1 is required to start using differential correction data.
3.1.6 Primary and secondary output
3.1.6.1 Introduction
u-blox GNSS receivers output various navigation results and data calculated as part of the
navigation solution. These include results such as position, altitude, velocity, status flags, accuracy
estimate figures, satellite/signal information and more.
The RCB-F9T can provide this output in two streams:
•Primary output: Reports the results of a full navigation solution using all capabilities of the
RCB-F9T,
•Secondary output: Reports the results of a GNSS standalone navigation solution.
Both the primary output and secondary output provide a similar set of information but the two
outputs report different results. The primary output is reported in the form of UBX-NAV-* messages,
while the secondary output is reported in the form of UBX-NAV2-* messages. Therefore, the UBX
message class can be used to distinguish between the primary output and the secondary output.
For the specification of the UBX-NAV2-* messages and for a full list of available UBX-NAV2-*
messages, see the applicable interface description [2].
UBX-22004121 - R01

3 Receiver functionality Page 12 of 64
C1-Public Early production information

RCB-F9T-Integration manual
The secondary output is complementary to the primary output. It does not provide the full
navigation solution of the primary output. It can be used to expand the applications of the
RCB-F9T to enable using a second navigation solution in parallel with the primary navigation
solution.
The rest of this section describes how to configure and use the secondary output, what is the
expected output behavior, and provides examples that illustrate potential uses for the secondary
output, while highlighting the differences between the primary and the secondary output.
3.1.6.2 Configuration
Configuring the secondary output to the application's needs requires:
• Enabling the secondary output
• Configuring the desired secondary output UBX-NAV2-* messages
• Optionally, configuring the properties of the secondary output navigation solution
The configuration items relevant to the secondary output are in the CFG-NAV2-* configuration
group. The configuration items for enabling and configuring the output rate of the UBX-NAV2-*
messages are in the CFG-MSGOUT-* group and are of the form CFG-MSGOUT-UBX_NAV2_*. An
example set of secondary output configuration items is shown in the table below. For all available
configuration items, see the applicable interface description [2].
Configuration item Description
CFG-NAV2-OUT_ENABLED Enables secondary output
CFG-NAV2-SBAS_USE_INTEGRITY Enables using SBAS integrity information in the secondary output
CFG-MSGOUT-UBX_NAV2_PVT_* Enables UBX-NAV2-PVT secondary output message
CFG-MSGOUT-UBX_NAV2_TIMEGPS_* Enables UBX-NAV2-TIMEGPS secondary output message
Table 8: Example secondary output configuration items
Enabling the secondary output: The first necessary step to enable the secondary output is to
configure the CFG-NAV2-OUT_ENABLED configuration item appropriately. This will enable the
secondary output navigation solution to run in parallel with the primary output navigation solution.
By default, the secondary output is disabled. Note that if you do not follow the next step, there will
be no secondary output visible in the RCB-F9T communication interfaces in the form of UBX-NAV2-
* messages.
Both primary and secondary output report a navigation solution computed at the same
navigation rate. Enabling the secondary output may affect the maximum achievable
navigation update rate due to the extra computational receiver load.
Configuring the desired secondary output UBX-NAV2-* messages: The second necessary step is
to configure the desired CFG-MSGGOUT-UBX_NAV2_* configuration items appropriately. These set
the message output rates for the UBX-NAV2-* messages that you wish to output. By default, all
UBX-NAV2-* message output rates are set to 0 and as such are not being output.
Due to the increased message output, the interface load will be higher while the secondary
output messages are enabled. Therefore, the interface baud rate may need to be adapted
accordingly. Alternatively, it is possible to configure the UBX-NAV2-* messages with a
different output rate from that of their primary output UBX-NAV-* counterparts.
Configuring the properties of the secondary output navigation solution: Optionally, it is possible
to configure the properties of the secondary output navigation solution in order to adapt it to the
application's needs.
UBX-22004121 - R01

3 Receiver functionality Page 13 of 64
C1-Public Early production information

RCB-F9T-Integration manual
A minimal subset of the primary output navigation solution configuration is available for the
secondary output navigation solution configuration. All such available configuration items are in the
CFG-NAV2-* configuration group (see applicable interface description [2]).
Configuring any of the CFG-NAV2-* configuration items changes the behavior of the secondary
output navigation solution only and not the primary output one. All such configuration items have a
primary output configuration counterpart and have the same default value as their primary output
configuration counterpart.
For example, the CFG-NAV2-SBAS_USE_INTEGRITY configuration item allows configuring the
SBAS integrity feature differently for the primary output and the secondary output. Its primary
output counterpart is the CFG-SBAS-USE_INTEGRITY configuration item and the default value of
both configuration items is the same.
3.1.6.3 Expected output behavior
Once the secondary output is enabled and the desired secondary output UBX-NAV2-* messages
are configured, the RCB-F9T will output both primary and secondary output data in the form of the
enabled UBX-NAV-* and UBX-NAV2-* messages respectively.
In every navigation epoch, a set of UBX-NAV-* messages will be output followed by another set of
UBX-NAV2-* messages. Both sets will be referring to the navigation solution of the same navigation
epoch.
Each set will be delimited at its end with a UBX-NAV-EOE or a UBX-NAV2-EOE message respectively.
In other words, a UBX-NAV-EOE message will be output at the end of the UBX-NAV-* class enabled
messages and a UBX-NAV2-EOE message will be output at the end of the UBX-NAV2-* class enabled
messages. For example, if only UBX-NAV-PVT, UBX-NAV2-PVT, UBX-NAV-TIMEGPS and UBX-NAV2-
TIMEGPS are enabled on the same port with message output rate 1, then every navigation epoch
output will be as follows: UBX-NAV-PVT, UBX-NAV-TIMEGPS, UBX-NAV-EOE, UBX-NAV2-PVT, UBX-
NAV2-TIMEGPS, UBX-NAV2-EOE.
Secondary output messages appear after the primary output messages. This results in a
higher latency for the secondary output messages than the primary output messages.
Contrary to UBX-NAV2-* messages, secondary output NMEA-NAV2-* messages are not
delimited by an NMEA-equivalent to UBX-NAV-EOE.
The specification of the UBX-NAV2-* messages resembles that of the UBX-NAV-* messages. The
payload specification of a UBX-NAV2 message is identical to the payload specification of its UBX-
NAV counterpart, allowing to easily adapt any existing message parsers. The primary output will
contain results and data reflecting the full navigation solution of the RCB-F9T. The secondary
output will contain results and data reporting a GNSS standalone navigation solution.
3.1.6.4 Example use cases
3.1.7 Legacy configuration interface compatibility
Although there is some backwards compatibility for the legacy UBX-CFG configuration messages,
users are strongly advised to adopt the configuration interface described in this document.
UBX-22004121 - R01

3 Receiver functionality Page 14 of 64
C1-Public Early production information

RCB-F9T-Integration manual
See Legacy UBX-CFG message fields reference section in the applicable interface description [2].
3.1.8 Navigation configuration
This section presents various configuration options related to the navigation engine. These options
can be configured through various configuration groups, such as CFG-NAVSPG-*, CFG-ODO-*, and
CFG-MOT-*.
3.1.8.1 Platform settings
u-blox receivers support different dynamic platform models (see the table below) to adjust the
navigation engine to the expected application environment. These platform settings can be
changed dynamically without performing a power cycle or reset. The settings improve the receiver's
interpretation of the measurements and thus provide a more accurate position output. Setting the
receiver to an unsuitable platform model for the given application environment is likely to result in
a loss of receiver performance and position accuracy.
The dynamic platform model can be configured through the CFG-NAVSPG-DYNMODEL
configuration item. The supported dynamic platform models and their details can be seen in Table
9 and Table 10 below.
Platform Description
Portable Applications with low acceleration, e.g. portable devices. Suitable for most situations.
Stationary (default) Used in timing applications (antenna must be stationary) or other stationary applications.
Velocity restricted to 0 m/s. Zero dynamics assumed.
Pedestrian Applications with low acceleration and speed, e.g. how a pedestrian would move. Low
acceleration assumed.
Automotive Used for applications with equivalent dynamics to those of a passenger car. Low vertical
acceleration assumed.
At sea Recommended for applications at sea, with zero vertical velocity. Zero vertical velocity assumed.
Sea level assumed.
Airborne <1g Used for applications with a higher dynamic range and greater vertical acceleration than a
passenger car. No 2D position fixes supported.
Airborne <2g Recommended for typical airborne environments. No 2D position fixes supported.
Airborne <4g Only recommended for extremely dynamic environments. No 2D position fixes supported.
Wrist Only recommended for wrist-worn applications. Receiver will filter out arm motion.
Table 9: Dynamic platform models
Platform Max altitude [m] Max horizontal
velocity [m/s]
Max vertical velocity
[m/s]
Sanity check type Max
position
deviation
Portable 12000 310 50 Altitude and velocity Medium
Stationary 9000 10 6 Altitude and velocity Small
Pedestrian 9000 30 20 Altitude and velocity Small
Automotive 6000 100 15 Altitude and velocity Medium
At sea 500 25 5 Altitude and velocity Medium
Airborne <1g 80000 100 6400 Altitude Large
Airborne <2g 80000 250 10000 Altitude Large
Airborne <4g 80000 500 20000 Altitude Large
Wrist 9000 30 20 Altitude and velocity Medium
Table 10: Dynamic platform model details
UBX-22004121 - R01

3 Receiver functionality Page 15 of 64
C1-Public Early production information

RCB-F9T-Integration manual
Applying dynamic platform models designed for high acceleration systems (e.g. airborne <2g) can
result in a higher standard deviation in the reported position.
If a sanity check against a limit of the dynamic platform model fails, then the position solution
is invalidated. Table 10 above shows the types of sanity checks which are applied for a particular
dynamic platform model.
3.1.8.2 Navigation input filters
The navigation input filters in CFG-NAVSPG-* configuration group provide the input data of the
navigation engine.
Configuration item Description
CFG-NAVSPG-FIXMODE By default, the receiver calculates a 3D position fix if possible but reverts to 2D
position if necessary (auto 2D/3D). The receiver can be forced to only calculate 2D
(2D only) or 3D (3D only) positions.
CFG-NAVSPG-CONSTR_ALT, CFG-
NAVSPG-CONSTR_ALTVAR
The fixed altitude is used if fixMode is set to 2D only. A variance greater than zero
must also be supplied.
CFG-NAVSPG-INFIL_MINELEV Minimum elevation of a satellite above the horizon in order to be used in the
navigation solution. Low elevation satellites may provide degraded accuracy, due to
the long signal path through the atmosphere.
CFG-NAVSPG-INFIL_NCNOTHRS,
CFG-NAVSPG-INFIL_CNOTHRS
A navigation solution will only be attempted if there are at least the given number of
SVs with signals at least as strong as the given threshold.
Table 11: Navigation input filter parameters
If the receiver only has three satellites for calculating a position, the navigation algorithm uses a
constant altitude to compensate for the missing fourth satellite. When a satellite is lost after a
successful 3D fix (min four satellites available), the altitude is kept constant at the last known value.
This is called a 2D fix.
u-blox receivers do not calculate any navigation solution with less than three satellites.
3.1.8.3 Navigation output filters
The result of a navigation solution is initially classified by the fix type (as detailed in the fixType
field of UBX-NAV-PVT message). This distinguishes between failures to obtain a fix at all ("No Fix")
and cases where a fix has been achieved, which are further subdivided into specific types of fixes
(e.g. 2D, 3D, dead reckoning).
The RCB-F9T firmware does not support the dead reckoning position fix type.
Where a fix has been achieved, a check is made to determine whether the fix should be classified as
valid or not. A fix is only valid if it passes the navigation output filters as defined in CFG-NAVSPG-
OUTFIL. In particular, both PDOP and accuracy values must be below the respective limits.
Important: Users are recommended to check the gnssFixOK flag in the UBX-NAV-PVT or
the NMEA valid flag. Fixes not marked valid should not be used.
UBX-NAV-STATUS message also reports whether a fix is valid in the gpsFixOK flag. This message
has only been retained for backwards compatibility and users are recommended to use the UBX-
NAV-PVT message.
3.1.8.3.1 Speed (3D) low-pass filter
The CFG-ODO-OUTLPVEL configuration item offers the possibility to activate a speed (3D) low-pass
filter. The output of the speed low-pass filter is published in the UBX-NAV-VELNED message (speed
field). The filtering level can be set via the CFG-ODO-VELLPGAIN configuration item and must be
comprised between 0 (heavy low-pass filtering) and 255 (weak low-pass filtering).
UBX-22004121 - R01

3 Receiver functionality Page 16 of 64
C1-Public Early production information

RCB-F9T-Integration manual
The internal filter gain is computed as a function of speed. Therefore, the level as defined in
the CFG-ODO-VELLPGAIN configuration item defines the nominal filtering level for speeds
below 5 m/s.
3.1.8.3.2 Course over ground low-pass filter
The CFG-ODO-OUTLPCOG configuration item offers the possibility to activate a course over ground
low-pass filter when the speed is below 8 m/s. The output of the course over ground (also named
heading of motion 2D) low-pass filter is published in the UBX-NAV-PVT message (headMot field),
UBX-NAV-VELNED message (heading field), NMEA-RMC message (cog field) and NMEA-VTG
message (cogt field). The filtering level can be set via the CFG-ODO-COGLPGAIN configuration item
and must be comprised between 0 (heavy low-pass filtering) and 255 (weak low-pass filtering).
The filtering level as defined in the CFG-ODO-COGLPGAIN configuration item defines the
filter gain for speeds below 8 m/s. If the speed is higher than 8 m/s, no course over ground
low-pass filtering is performed.
3.1.8.3.3 Low-speed course over ground filter
The CFG-ODO-USE_COG activates this feature and the CFG-ODO-COGMAXSPEED, CFG-ODO-
COGMAXPOSACC configuration items offer the possibility to configure a low-speed course over
ground filter (also named heading of motion 2D). This filter derives the course over ground from
position at very low speed. The output of the low-speed course over ground filter is published in the
UBX-NAV-PVT message (headMot field), UBX-NAV-VELNED message (heading field), NMEA-RMC
message (cog field) and NMEA-VTG message (cogt field). If the low-speed course over ground filter
is not configured, then the course over ground is computed as described in section Freezing the
course over ground.
3.1.8.4 Static hold
Static hold mode allows the navigation algorithms to decrease the noise in the position output when
the velocity is below a pre-defined "Static Hold Threshold". This reduces the position wander caused
by environmental factors such as multi-path and improves position accuracy especially in stationary
applications. By default, static hold mode is disabled.
If the speed drops below the defined "Static Hold Threshold", the static hold mode will be activated.
Once static hold mode has been entered, the position output is kept static and the velocity is set to
zero until there is evidence of movement again. Such evidence can be velocity, acceleration, changes
of the valid flag (e.g. position accuracy estimate exceeding the position accuracy mask, see also
section Navigation output filters), position displacement, etc.
The CFG-MOT-GNSSDIST_THRS configuration item additionally allows for configuration of
distance threshold. If the estimated position is farther away from the static hold position than this
threshold, static mode will be quit. The CFG-MOT-GNSSSPEED_THRS configuration item allows you
to set a speed that the static hold will release.
UBX-22004121 - R01

3 Receiver functionality Page 17 of 64
C1-Public Early production information

RCB-F9T-Integration manual
Figure 2: Position publication in static hold mode
Figure 3: Flowchart of the static hold mode
UBX-22004121 - R01

3 Receiver functionality Page 18 of 64
C1-Public Early production information

RCB-F9T-Integration manual
3.1.8.5 Freezing the course over ground
If the low-speed course over ground filter is deactivated or inactive (see section Low-speed course
over ground filter), the receiver derives the course over ground from the GNSS velocity information.
If the velocity cannot be calculated with sufficient accuracy (e.g., with bad signals) or if the absolute
speed value is very low (under 0.1 m/s) then the course over ground value becomes inaccurate too.
In this case the course over ground value is frozen, i.e. the previous value is kept and its accuracy
is degraded over time. These frozen values will not be output in the NMEA messages NMEA-RMC
and NMEA-VTG unless the NMEA protocol is explicitly configured to do so (see NMEA protocol
configuration in the applicable interface description [2]).
Figure 4: Flowchart of the course over ground freezing
3.2 SBAS
Whilst the RCB-F9T can make use of SBAS satellites, experience has shown that employing these
signals can degrade the timing performance and hence SBAS use is not enabled by default. The
following section describes the receiver operation when SBAS reception is required by users.
The RCB-F9T is capable of receiving multiple SBAS signals concurrently, even from different SBAS
systems (WAAS, EGNOS, MSAS, etc.). They can be tracked and used for navigation simultaneously.
Every SBAS satellite that broadcasts ephemeris or almanac information can be used for navigation,
just like a normal GNSS satellite.
For receiving correction data, the RCB-F9T automatically chooses the best SBAS satellite as its
primary source. It will select only one since the information received from other SBAS satellites is
redundant and could be inconsistent. The selection strategy is determined by the proximity of the
satellites, the services offered by the satellite, the configuration of the receiver (test mode allowed/
disallowed, integrity enabled/disabled) and the signal link quality to the satellite.
If corrections are available from the chosen SBAS satellite and used in the navigation calculation, the
differential status will be indicated in several output messages such as UBX-NAV-PVT, UBX-NAV-
STATUS, UBX-NAV-SAT, NMEA-GGA, NMEA-GLL, NMEA-RMC and NMEA-GNS (see the applicable
UBX-22004121 - R01

3 Receiver functionality Page 19 of 64
C1-Public Early production information

RCB-F9T-Integration manual
interface description [2]). The message UBX-NAV-SBAS provides detailed information about which
corrections are available and applied.
The most important SBAS feature for accuracy improvement is ionosphere correction. The
measured data from regional Ranging and Integrity Monitoring Stations (RIMS) are combined to
make a Total Electron Content (TEC) map. This map is transferred to the receiver via SBAS satellites
to allow a correction of the ionosphere error on each received signal.
Message type Message content Source
0(0/2) Test mode All
1 PRN mask assignment Primary
2, 3, 4, 5 Fast corrections Primary
6 Integrity Primary
7 Fast correction degradation Primary
9 Satellite navigation (ephemeris) All
10 Degradation Primary
12 Time offset Primary
17 Satellite almanac All
18 Ionosphere grid point assignment Primary
24 Mixed fast / long-term corrections Primary
25 Long-term corrections Primary
26 Ionosphere delays Primary
Table 12: Supported SBAS messages
Each satellite services a specific region and its correction signal is only useful within that region.
Planning is crucial to determine the best possible configuration, especially in areas where signals
from different SBAS systems can be received:
•Example 1 - SBAS receiver in North America: In the eastern parts of North America, make sure
that EGNOS satellites do not take preference over WAAS satellites. The satellite signals from
the EGNOS system should be disallowed by using the PRN mask.
•Example 2 - SBAS receiver in Europe: Some WAAS satellite signals can be received in the
western parts of Europe, therefore it is recommended that the satellites from all but the
EGNOS system should be disallowed using the PRN mask.
Although u-blox receivers try to select the best available SBAS correction data, it is
recommended to configure them to exclude unwanted SBAS satellites.
To configure the SBAS functionalities use the CFG-SBAS-* configuration group.
Parameter Description
CFG-SIGNAL-SBAS_ENA Enabled/disabled status of the SBAS subsystem
CFG-SBAS-USE_TESTMODE Allow/disallow SBAS usage from satellites in test mode
CFG-SBAS-USE_RANGING Use the SBAS satellites for navigation (ranging)
CFG-SBAS-USE_DIFFCORR Combined enable/disable switch for fast-, long-term and ionosphere corrections
CFG-SBAS-USE_INTEGRITY Apply integrity information data
CFG-SBAS-PRNSCANMASK Allows selectively enabling/disabling SBAS satellites
Table 13: SBAS configuration parameters
When SBAS integrity data are applied, the navigation engine stops using all signals for
which no integrity data are available (including all non-GPS signals). It is not recommended
UBX-22004121 - R01

3 Receiver functionality Page 20 of 64
C1-Public Early production information