radio-controlled-clock
A radio-controlled clock receives longwave radio signals transmitted by a national time-standard station and automatically corrects its built-in quartz oscillator. In Japan the signal is JJY (40 kHz / 60 kHz), operated by NICT. As long as the clock keeps receiving the signal, it stays in step with the national time standard; between receptions it runs on its own quartz accuracy.
The time signal is transmitted via amplitude modulation (AM) of the carrier wave, encoding one bit per second. A complete frame carrying the minute, the hour, the day of year, the last two digits of the year, and the day of the week is assembled over 60 seconds (one minute); the month and the day of the month are not transmitted, and the receiver works them out from the day of year. Most radio-controlled clocks attempt automatic reception once or several times during the night, when signal conditions are best. If reception fails, the clock continues to run as a standard quartz clock with accuracy of roughly plus or minus 15 seconds per month.
Several countries operate their own longwave time signal stations: Germany's DCF77 (77.5 kHz), the United Kingdom's MSF (60 kHz), the United States' WWVB (60 kHz), and China's BPC (68.5 kHz). Multi-band radio-controlled clocks can receive more than one of these signals, so they keep correcting themselves from the local broadcast when the wearer travels abroad (on many models the displayed city and time-zone offset still have to be switched by hand).
Was this article helpful?
nict
NICT is Japan's national research institute responsible for generating, maintaining, and distributing Japan Standard Time (JST), operating a fleet of atomic clocks and transmitting the JJY time signal.
atomic clock
An atomic clock measures time by using the quantum-mechanical transition frequency of atoms as its reference, achieving accuracies on the order of one second in hundreds of millions of years and forming the backbone of modern timekeeping.
jst
JST (Japan Standard Time) is the standard time of Japan at UTC+9, based on the 135th meridian east. Japan does not observe daylight saving time.
Understand how daylight saving time works, which countries observe it, when transitions occur, and how DST complicates international scheduling.
A world clock is more than a novelty. With remote teams and international travel, it becomes a thinking tool for scheduling meetings fairly, planning flight connections, and avoiding daylight saving surprises. This article walks through real scenarios where a world clock earns its place on screen.
From cesium fountain clocks to optical lattice clocks, atomic timekeeping defines the second and underpins GPS, financial trading, and physics experiments. This article explains the principles, the precision levels achieved, and why ultra-stable clocks matter for invisible infrastructure.