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Wikipedia article

Related wiki pages GMT, Time Beacons, Modes

What are GMT, UTC and Zulu?

GMT (Greenwich Mean Time) was introduced when the concepts of longitude and latitude cane to be used for sea navigation. It is the line of longitude - passing though Greenwich Great Britain that all times around the world were compared to. This longitude line is known as the Prime Meridian

UTC (Coordinated Universal Time) was introduced when the accuracy of clocks improved to the extent that variations in the rotation of the earth caused measurable errors in time calculations. UTC now replaces the GMT

Zulu the letter Z in the phonetic alphabet. The time designation used in aviation and defence.

Time in Amateur Radio

Various digital modes are very dependent on accurate time measurements:

  • WSPR requires a time accuracy within 1 second of UTC. WSPR operates in 2 minute time slots with computer links to effect reception reports.
  • JT65HF also requires high accuracy time coordination

Further reading