Contact person
Gustav Jönsson
Forskare
Contact Gustav
Calibration of GNSS Equipment for Accurate Time and Frequency
By calibrating GNSS receiver equipment, time and frequency obtained from GNSS (e.g. GPS and Galileo) become both traceable and accurate, which is a requirement in many industries. RISE calibrates equipment both in our laboratory and on-site at the customer, in accordance with the CIPM-MRA, fulfilling global requirements for traceability.
Time and Frequency from GNSS
Time from global navigation satellite systems (GNSS, such as the American GPS and the European Galileo) is easily accessible and precise. Signals in space rarely deviate more than a few nanoseconds from the global time scale UTC.
On the ground, however, the situation is different. Several factors affect the accuracy of time from when it leaves the satellite constellation until it reaches the point of use. Delays in the atmosphere and ionosphere can to some extent be handled at the system level, but local effects—such as signal reflections in the receiver antenna’s surroundings and systematic delays in the antenna, antenna cable, receiver, and the user’s own time distribution system—must be managed through local comparisons against an accurate reference, i.e. calibration. A typical delay in cabling is 5 ns per meter of signal cable.
Frequency transfer via GNSS is less sensitive to local delays, but the equipment must still be calibrated to be considered traceable.
To obtain time from GNSS, a user may employ a GNSS-disciplined oscillator that generates a local signal synchronized and syntonized to a GNSS time scale. Alternatively, the user may connect a time source to a GNSS receiver for time transfer, which compares the user’s time against GNSS time.
When Is Calibration Needed?
The need for calibration depends on the requirements of the specific application. Regular calibration of individual installations is recommended when the requirements for relative frequency accuracy are better than 10⁻¹² over a day. For time, regular calibration is recommended when accuracy requirements are better than 100 ns.
In the Lab or in the Field
RISE offers calibration of GNSS-disciplined oscillators and GNSS receivers intended for timekeeping. Calibration can be performed either at the customer’s site or in RISE laboratories, depending on the customer’s needs and the specific conditions of the installation.
Delivery is carried out according to agreement with the customer.
