There has been much discussion recently implying that Loran-C chain synchronisation using
‘System Area Monitor’ (SAM) control and using ‘Time of Transmission (or Emission)’
(TOT or TOE) are incompatible mechanisations of Loran-C chain time management
because of their differing impact on users. Further, the mechanisation of UTC
synchronisation is described as either satellite (GPS/GLONASS) based or Loran Chain
measurement based, thereby excluding integrated use of both techniques for reliability.
These differences are not mutually exclusive. Well-defined chain synchronisation can
logically apply all measurement and control techniques as well as providing improved
accuracy. This paper defines synchronisation and describes the history of Loran-C
synchronisation control and the current methods employed. The existence of Cesium
Standards at Loran stations, and the recent introduction of digital signal processing
receivers, have greatly changed the potential for extremely precise timing control, detection
of extraordinary timing changes, and the maintenance of very tight UTC synchronisation.
This paper describes a number of techniques for defining, observing and applying the various
sources of timing information, optimising performance for users and simplifying
implementation for service providers.