WWVB is a special NIST time signal radio station in Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks throughout North America use to synchronize themselves. The signal transmitted from WWVB is a continuous 60 kHz carrier wave, derived from a set of atomic clocks located at the transmitter site. A 1 bit-per-second time code, which is derived from the same set of atomic clocks, is then modulated onto the carrier wave using a technique described equivocally as either pulse width modulation or amplitude-shift keying. The time in this code is given in UTC, which the radio-controlled clocks then have to convert to their own local time. A single complete frame of time code lasts one minute. As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ... Horsetooth Rock, atop Horsetooth Mountain, is often used as a symbol of Fort Collins Fort Collins, situated on the Cache la Poudre River, is the largest city and county seat of Larimer County, Colorado. ... WWV is the callsign of NISTs shortwave radio station located in Fort Collins, Colorado. ... A radio clock A radio clock is a clock that is synchronized by a time code transmitted by a radio transmitter connected to a time standard such as an atomic clock. ... Jump to: navigation, search World map showing North America (geographically) A satellite composite image of North America North America is a continent in the northern hemisphere, bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the south by the Caribbean Sea, and... A kilohertz (kHz) is a unit of frequency equal to 1,000 hertz (1,000 cycles per second). ... Atomic clock Chip-Scale Atomic Clock Unveiled by NIST An atomic clock is a type of clock that uses an atomic resonance frequency standard as its counter. ... Pulse-width modulation of a signal or power source involves the modulation of its duty cycle to either convey information over a communications channel or control the amount of power sent to a load. ... Amplitude-shift keying (ASK) is a form of modulation which represents digital data as variations in the amplitude of a carrier wave. ... UTC also stands for the University of Tennessee at Chattanooga Coordinated Universal Time or UTC, also sometimes referred to as Zulu time, the basis for civil time, differs by an integral number of seconds from atomic time and a fractional number of seconds from UT1. ...

Antennas

There are two identical antennas used to radiate the WWVB signal. Both antennas are 122 metres tall, and their centres are separated by 857 metres. The physical configuration of each antenna is a diamond-shaped "top loaded monopole", consisting of several cables spread on a flat plane from the top of their support towers, and a vertical cable that connects the top plane to a "helix house" on the ground. Each helix house contains a dual fixed-variable inductor system, which is used to keep the antenna system at its maximum radiating efficiency.

Modulation Format

At the start of each UTC second, the WWVB 60 kHz carrier, which has a normal power of 50 kW, is reduced in power by 17 dB. Before July 12, 2005, the power reduction was 10 dB. The type of bit transmitted on each second is determined by when the carrier wave is returned to normal power within that second. If the carrier power is returned to normal in one-fifth of a second, or 0.2 s, from when it was reduced, the bit is a zero. If the carrier power is returned to normal in one half-second, or 0.5 s, the bit is a one. If the carrier power is returned to normal in four-fifths of a second, or 0.8 s., the bit is a reference bit. If two reference bits are sent consecutively, the start of the second reference bit indicates both the top of the UTC minute and the "on-time marker" for the time code that follows it. Power kilowatt (symbol: kW) is a unit for measuring power, equal to one thousand watts. ... The decibel (dB) is a measure of the ratio between two quantities, and is used in a wide variety of measurements in acoustics and electronics. ... Jump to: navigation, search July 12 is the 193rd day (194th in leap years) of the year in the Gregorian Calendar, with 172 days remaining. ... Jump to: navigation, search 2005(MMV) is a common year starting on Saturday of the Gregorian calendar. ...

WWVB also has a method of station identification, which it transmits by a 45° shift in the phase of its carrier wave at ten minutes past the hour, and a -45° shift five minutes later. This phase step is equivalent to "cutting and pasting" approximately 2.08 µs of the unshifted carrier wave. A microsecond is an SI unit of time equal to one millionth (10-6) of a second. ...

Jump to: navigation, search Image File history File links WWVB_Time_Code_Format. ...

Propagation

Since WWVB's longwave signal tends to propagate better along the ground, it requires a shorter and less turbulent path to get to the radio receivers than WWV's shortwave signal, which is strongest when it bounces between the ionosphere and the ground. This results in the WWVB signal having greater accuracy than the WWV signal as received at the same site. Also, since longwave signals tend to propagate much further at night, the WWVB signal can reach a larger coverage area during that time period, which is why many radio-controlled clocks are usually programmed to automatically synchronize themselves with the WWVB time code during local nighttime hours. Longwave radio frequencies are those below 500 kHz, which correspond to wavelengths longer than 600 meters. ... A Grundig Shortwave receiver Shortwave radio operates between the frequencies of 3,000 kHz and 30 MHz (30,000 kHz) and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than those commonly in use at... The ionosphere is the part of the atmosphere that is ionized by solar radiation. ...

The radiation pattern of WWVB antennas is designed to present a field strength of at least 100 μV/m² over most of the continental United States and Southern Canada during some portion of the day. Although this value is well above the thermal noise floor, man made noise and local interference from a wide range of electronic equipment can easily swamp out the signal. Positioning receiving antennas away from electronic equipment helps to reduce the effects of local interference. In telecommunications, and particularly in radio, signal strength is the measure of how strong a signal is. ... Johnson-Nyquist noise (sometimes thermal noise, Johnson noise or Nyquist noise) is the noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor, which happens without any applied voltage, due to the random thermal motion of the charge carriers (the electrons). ... In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system. ...

Antenna Reuse with former WWVL

Another time signal station, WWVL, began transmitting a 500 Watt signal on 20 kHz in August 1963. It used Frequency Shift Keying (FSK), shifting from 20 kHz to 26 kHz, to send data. The WWVL broadcast was discontinued in July 1972. A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ... Frequency-shift keying (FSK) is frequency modulation in which the modulating signal shifts the output frequency between predetermined values. ...

As part of a recent WWVB modernization programme, the decommissioned WWVL antenna was used to radiate the WWVB signal. This allowed for a WWVB transmitter power increase to 50 kW, as well as providing a backup antenna that now facilitates routine maintenance.

A radio clock A radio clock is a clock that is synchronized by a time code transmitted by a radio transmitter connected to a time standard such as an atomic clock. ... BPM is the Peoples Republic of Chinas national time signal service, operated by the Chinese Academy of Sciences. ... Chu could refer to: The Chu river valley in modern Kyrgyzstan. ... DCF77 is a longwave time signal radio station. ... Jump to: navigation, search Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ... HBG Prangins is a large transmission facility near Prangins, Switzerland. ... JJY is the callsign of a longwave time signal radio station similar to WWVB. The station is located in Japan, operated by a branch of the Japanese government known as the National Institute of Information and Communications Technology. ... The MSF time signal is a broadcast from the VLF transmitter Rugby near Rugby, Warwickshire based on time standards maintained by the British National Physical Laboratory. ... RWM is the callsign of a shortwave radio station in Moscow, Russia. ... VNG was Australias national time signal service, and operated on 2500, 5000, 8638, 12984, and 16000 kHz. ... WWV is the callsign of NISTs shortwave radio station located in Fort Collins, Colorado. ... WWVH is the callsign of NISTs shortwave radio time signal station in Kekaha, on the island of Kauai in the state of Hawaii. ... YVTO is the callsign of the official time signal from the Juan Manuel Cagigal Naval Observatory in Caracas, Venezuela. ...

External links

• NIST Radio Station WWVB
• WWVB Radio Controlled Clocks: Recommended Practices for Manufacturers and Consumers