Radio Sync includes a radio receiver, which receives a signal that
comes from a place where an atomic clock is located.
In the United States, the signals received by
radio-controlled clocks originate from
NIST Radio Station WWVB, which is located near Fort Collins, Colorado. WWVB
broadcasts on a frequency of 60 kHz. The Radio Sync receiver is permanently
tuned to receive this 60 kHz signal.
The 60 kHz signal is located in a part of
the radio spectrum called LF, which stands for low frequency. This is an
appropriate name, because the FM radio and TV broadcasts that we are
accustomed to listening to use frequencies thousands of times higher. The
lowest frequency received by any of the other radios in your house is
probably 530 kHz, the bottom of the AM broadcast band. Even that frequency
is nearly 10 times higher than the WWVB signal.
At 60 kHz, there isnt enough room on the
signal (bandwidth) to carry a voice or any type of audio information.
Instead, all that is sent is a code, which consists of a series of binary
digits, or bits, which have only two possible values (0 or 1). These bits
are generated at WWVB by raising and lowering the power of the signal. They
are sent at a very slow rate of 1 bit per second, and it takes a full minute
to send a complete time code, or a message that tells the clock the current
date and time. When you turn a radio-controlled clock on, it will probably
miss the first time code, so it usually takes more than one minute to set
itself (sometimes 5 minutes or longer) depending on the signal quality and
the receiver design.
Once the receiver has decoded the signal
from WWVB, it will synchronize its own RTC clock to the message received by
radio. The time broadcast by WWVB is Coordinated Universal Time (UTC), or
the time kept at the Prime Meridian that passes through Greenwich, England.
The ClockWatch software uses the Windows time zone setting in the Windows
control panel to make the correction to local time.
Once Radio Sync has synchronized, it
continues to update every minute. In between synchronizations, the receiver
keeps time using real time clock.
More on Radio Controlled Clock Technology