Final Presentation of Element 2-063 "Digital Modem for Two-Way Satellite Time Transfer"

Last Updated: 18/03/2025 09:23     Created at: 18/03/2025 09:23

Slides are now available! On 10th March 2025 ELTVOR Instruments s.r.o. (CZ) presented the first digital Two-Way Satellite Time and Frequency Transfer (TWSTFT) modem in Europe (NAVISP EL2-063 – “Digital Modem for Two-Way Satellite Time Transfer”). The TWSTFT technique requires a modem at two or more ground stations to carry out highly accurate time and frequency transfer via a satellite bent-pipe transponder in GEO, independently of GNSS.

The ELTVOR modem has been developed using digital radio technology to operate in real-time with a direct interface to the ground station clock. Up to eight ground stations can be compared simultaneously using one modem, however more stations can be tracked using multiplexing or daisy chaining of several modems. The modem transmits a fully digitally defined signal, compliant with other traffic on the satellite transponder without compromising the timing information. Modem chiprates range from 1M to 20M chips/s and the intermediate frequency (IF) is 70MHz typically used by existing modems, however it can operate with 140MHz IF. This new development is backward compatible with currently used analogue modem technology.

Laboratory testing of the modem loopback performance was very good  with a jitter level of 0.5ps (where ps = picoseconds or 10−12 seconds) rms (root mean square), improving on legacy devices, and time stability of the order of 200fs (where fs = femtoseconds or 10−15 seconds) after 100s. Reception tests using one station in CZ with a 2.4M dish and Ku band terminal connected to the modem via GEO (SIGSO) achieved 65ps rms at an averaging time of 1s. A Two-Way transmission test between Pecny CZ and ESTEC NL (780km baseline) with identical modems at each station gave very good results, which were however limited by factors such as local variations in UTC at the 1ns (where ns = nanoseconds or 10−9 seconds) level. 

Further tests are proposed for a future NAVISP EL2 activity. ELTVOR Instruments is in conversation with National Metrology Institutes about future experiments, as well as commercial opportunities to upgrade current TWSTFT systems and to bring new players into the international TWSTFT comparison contributing to UTC. The modem is now available for order.

Funded by NAVISP Element 2, which drives competitiveness in Europe’s Positioning, Navigation, and Timing (PNT) sector, this project has achieved commercial success and demonstrates the advancement of European Time Transfer capabilities. 

The presentation slides are available here.