An atomic clock, or radio controlled clock is set to receive and process an atomic clock synchronization signal broadcast from an actual atomic clock, usually operated by a government agency (i.e. WWVB in Boulder, Colorado). As reliable as they may seem, atomic clocks have a number of inherent restrictions.
Radio controlled clocks are dependent upon time signal stations. The clocks will not work well if the atomic clock signals are too far away.
A Radio Frequency Wireless Clock System receives a dependable time from any SNTP/NTP server or GPS satellite.
Radio controlled clocks rely on picking up radio waves from the time signal stations. The ability to pick up a signal depends on the device pointing towards the station. Reliability also depends on favorable atmospheric conditions, with high-pressure or low-lying fog potentially affecting reception.
RF Wireless Synchronized Clocks use the Frequency Hopping Spread Spectrum (FHSS). The time signal "hops" from frequency to frequency, ensuring the clocks will receive the correct time despite interference on any of the frequencies.
Distance and Accuracy
The method by which atomic clocks work has an inherent limitation - the time it takes for the radio signal to reach the clock. The signal gives the time at the point the signal left the station, but the actual time at which it reaches your clock will be slightly later. The National Institute of Standards and Technology (NIST) notes this discrepancy can mean considerable inaccuracy in those areas at the farthest reaches of the signal from a particular station, such as the east and west coast of the United States.
A Radio Frequency Transmitter consistently receives time data from satellites and sends a time signal to analog or digital clocks.
Consumer atomic clocks use a quartz crystal oscillator to keep time in between checking and synchronizing with a time signal station. The performance of this quartz may vary, and this factor will become more significant if reception problems prevent synchronization for an extended time signal. Your clock could potentially gain or lose time. This discrepancy will depend on the level of precision with which your clock displays the time.
RF Wireless digital clocks receive a time update every 20 seconds.
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