When connected to a GNSS antenna that receives a GNSS signal, SecureSync can use GNSS as an input reference. The factory default configuration allows GNSS satellites to be received/tracked with no additional user intervention required.
However, there are several user-configurable GNSS settings:
- The Receiver Mode function allows the GNSS receiver to operate in either a stationary mode (“Standard” or “Single Satellite” modes), or in a mobile mode environment e.g., in a vehicle, ship or aircraft.
- Offset [ns]: to account for antenna cable delays and other latencies
- Receiver dynamics
(supported only by u-blox M8T and Trimble Res-T receivers): to optimize performance for land, sea or air operation
- The ability to delete the stored GNSS position information (latitude, longitude and antenna height).
- The option to determine when a resurvey is to be performed (supported only by newer GNSS receivers).
To configure the GNSS Receiver Mode for your SecureSync unit:
- Navigate to INTERFACES > REFERENCES: GNSS 0. The GNSS 0 Status panel will open.
- Click Edit in the bottom-left corner. The GNSS 0 configuration window will open:
- Select the desired Receiver Mode, and click Submit.
GNSS Receiver Modes
The receiver modes are:
The default GNSS receiver mode is the Standard Mode: It is the most accurate, and hence the preferred GNSS receiver mode.
The Standard Mode can be used only for stationary applications, i.e. the SecureSync unit will not be moved. Also, it must be able to track initially at last four satellites in order to complete the survey. (Once the survey is completed, less than four satellites will provide a valid Time and 1PPS.)
About the GNSS Survey
In the Standard Mode the so-called GNSS survey will initially be performed, once at least four GNSS satellites become available. The GNSS survey is used to determine the exact position and time; it takes 2000 seconds (33 minutes) to complete a survey. During the survey, the GNSS receiver must continue to track at least four satellites, otherwise the GNSS survey will not complete.
Upon completion of the GNSS survey the GNSS receiver will lock-in the calculated GNSS position and will enter Standard Mode. Once in Standard Mode, the GNSS survey will only be performed again if:
- the equipment will be relocated to another location and the receiver detects this (applies to most Trimble receivers)
- the Receiver Dynamics is set to Resurvey after every reboot (this feature is available only with u-blox receivers and Trimble RES-SMT-GG receivers; it can be turned off, see Setting GNSS Receiver Dynamics.)
- you manually delete the GNSS position, see Deleting the GNSS Receiver Position.
In the event that SecureSync cannot complete a GNSS survey within 24 hours (e.g., the survey progress does not go beyond 99%), see Single Satellite GNSS Receiver Mode.
The Single Satellite Mode is designed for use cases in which it is not possible for the GNSS receiver to track at least four GNSS satellites for at least 33 minutes continuously in a 12-hour time window so as to complete the GNSS survey, i.e. obtain a 3-D fix. In such cases, SecureSync cannot operate in Standard Mode. This occurs frequently in areas with limited view of the sky (e.g., "urban canyons").
In Single Satellite Mode, the GNSS receiver will be considered a valid input reference as long as:
- the receiver was able to complete a survey during a time window with good satellite reception, OR you have manually entered a valid position for your antenna location (instructions can be found under Manually Setting the GNSS Position and Determining Your Position.)
- the GNSS receiver continues to track at least one qualified satellite.
Note that SecureSync is designed to provide the most accurate time in Standard Mode, hence the Single Satellite Mode should only be used if the GNSS receiver could not complete a survey. Note also that Single Satellite Mode can only be used if the SecureSync unit remains stationary at all times.
In Mobile Mode no surveys will be carried out since the position status is updated in near real-time. SecureSync will go into synchronization shortly after beginning to track satellites.
The Mobile Mode should only be selected if your SecureSync unit will NOT remain stationary at all times, i.e. instead of being operated in a building, it is installed in a mobile platform (such as a vehicle, ship, plane, etc.).
Note: With SecureSync's GNSS receiver configured in Mobile Mode, the specified accuracies of SecureSync will be degraded to less than three times that of Standard Mode. Standard Mode accuracy of the receiver is less than 50 ns to GPS/UTC (1 sigma), hence Mobile Mode is less accurate than 150 ns to GPS/UTC time (1 sigma).