3 ms·

>It's amazing what's connected to GPS that ought not to be. Is there a practical alternative for high-accuracy synchronisation? You could make the case for a b

• throw0101c 3y ago
  > You could make the case for a backup shortwave receiver, but I'm not sure that's any more reliable than GNSS. GPS L1 power when received is -128.43 dBm (-158.43 dBW): * https://apps.fcc.gov/els/GetAtt.html?id=110032&x= https://apps.fcc.gov/els/GetAtt.html?id=110032&x= * https://support.spirent.com/index?page=content&id=FAQ14116 https://support.spirent.com/index?page=content&id=FAQ14116 * https://support.spirent.com/SC_KnowledgeView?Id=FAQ14116 https://support.spirent.com/SC_KnowledgeView?Id=FAQ14116 Meanwhile (e.g.) Loran-C is -60 dBm: * https://www.qsl.net/df3lp/projects/lfscan/index.html https://www.qsl.net/df3lp/projects/lfscan/index.html So GPS signals are below the noise floor, but Loran-C are 50 dBm are above it: * https://www.prc68.com/I/A2100F.shtml https://www.prc68.com/I/A2100F.shtml So while something like Loran-C didn't have global coverage while it was still active: * https://en.wikipedia.org/wiki/File:NGA-Atlantic_Loran.png https://en.wikipedia.org/wiki/File:NGA-Atlantic_Loran.png * https://en.wikipedia.org/wiki/File:NGA-Pacific_Loran.png https://en.wikipedia.org/wiki/File:NGA-Pacific_Loran.png * https://en.wikipedia.org/wiki/File:Loranstationscrkl.jpg https://en.wikipedia.org/wiki/File:Loranstationscrkl.jpg * https://timeandnavigation.si.edu/multimedia-asset/loran-day-and-night-coverage-1945 https://timeandnavigation.si.edu/multimedia-asset/loran-day-... it did cover large populations centres, as well as major marine shipping and air traffic routes. Another reason why it didn't the coverage wasn't global was a lot of transmitters (e.g., the continents of South America and Africa). With regards to timing accuracy, a paper fro 1992: > The accuracy of time comparison by means of the reception of common time signals, namely, LORAN-C and Global Positioning System (GPS), is examined. Differences of UTC from the emission times of these two radio wave signals measured at four Japanese stations and one U.S. station are analyzed and compared with the clock comparison reports published by the Bureau International des Poids et Mesures. The accuracy of the time comparison via LORAN-C signals of the northwest Pacific chain is about 3.61 μs and that via GPS is 0.14 μs. The accuracy analysis reveals the existence of systematic errors at the individual stations. In LORAN-C, the most serious error comes from those in the delay time calibration of receiving instruments and estimation of the propagation delay over land. Calibration of the clocks by a portable clock improves the accuracy of the GPS method to the accuracy of the GPS signals. * https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92RS01010 https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92RS... * https://doi.org/10.1029/92RS01010 https://doi.org/10.1029/92RS01010 eLoran can get to the 100s- to 10s-of-ns range: * https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7697629/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7697629/