WWV - AbsoluteAstronomy.com

WWV is the call sign

Call sign

In broadcasting and radio communications, a call sign is a unique designation for a transmitting station. In North America they are used as names for broadcasting stations...

of the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...

's (NIST) HF

High frequency

High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...

("shortwave

Shortwave

Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...

") radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

station in Fort Collins, Colorado

Fort Collins, Colorado

Fort Collins is a Home Rule Municipality situated on the Cache La Poudre River along the Colorado Front Range, and is the county seat and most populous city of Larimer County, Colorado, United States. Fort Collins is located north of the Colorado State Capitol in Denver. With a 2010 census...

. WWV continuously transmits official U.S. Government frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

and time signal

Time signal

A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:...

s on 2.5, 5, 10, 15 and 20 MHz. These carrier frequencies

Carrier wave

In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...

and time signals are controlled by local atomic clock

Atomic clock

An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...

s traceable to NIST's primary standard in Boulder, Colorado

Boulder, Colorado

Boulder is the county seat and most populous city of Boulder County and the 11th most populous city in the U.S. state of Colorado. Boulder is located at the base of the foothills of the Rocky Mountains at an elevation of...

by GPS common view observations and other time transfer

Time transfer

Time transfer is a scheme where multiple sites share a precise reference time. Time transfer solves problems such as astronomical observatories correlating observed flashes or other phenomenon with each other, as well as cell phone towers coordinating handoffs as a phone moves from one cell to...

methods. NIST also operates the very similar radio station WWVH

WWVH

WWVH is the callsign of the U.S. National Institute of Standards and Technology's shortwave radio time signal station in Kekaha, on the island of Kauai in the state of Hawaii....

in Kauai

Kauai

Kauai or Kauai, known as Tauai in the ancient Kaua'i dialect, is geologically the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago, and the 21st largest island in the United States. Known also as the "Garden Isle",...

, Hawaii

Hawaii

Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

. WWV and WWVH make recorded announcements; since they share frequencies, WWV uses a male voice to distinguish itself from WWVH, which uses a female voice. They also make other recorded announcements of general interest, e.g., the GPS satellite constellation status and severe oceanic weather warnings. WWV shares its Fort Collins site with radio station WWVB

WWVB

WWVB is a NIST time signal radio station near Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks in most of North America use to synchronize themselves. The signal transmitted from WWVB is a continuous 60 kHz carrier wave, derived from a set of atomic...

that transmits carrier and time code (no voice) on 60 kHz in the low frequency (LF)

Low frequency

Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

band.

Launch

WWV is the oldest continuously-operating radio station in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, first going on the air from Washington, D.C.

Washington, D.C.

Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

in May 1920, approximately six months before the launch of KDKA

KDKA (AM)

KDKA is a radio station licensed to Pittsburgh, Pennsylvania, USA. Created by the Westinghouse Electric Corporation on November 2, 1920, it is one of the world's first modern radio stations , a distinction that has also been challenged by other stations, although it has claimed to be the first in...

. The station first broadcast Friday evening concerts on 600 kHz, and its signal could be heard 40 kilometres (24.9 mi) from Washington. On December 15, 1920, WWV began broadcasting on 750 kHz, distributing Morse code

Morse code

Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

news reports from the Department of Agriculture

United States Department of Agriculture

The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...

. This signal could be heard up to 300 kilometres (186.4 mi) from Washington. These news broadcasts ended on April 15, 1921.

Standard frequency signals

At the end of 1922, WWV's purpose shifted to broadcasting standard frequency signals. These signals were desperately needed by other broadcasters, because equipment limitations at the time meant that the broadcasters could not stay on their assigned frequencies. Testing began on January 29, 1923, and frequencies from 200 to 545 kHz were broadcast. Frequency broadcasts officially began on March 6, 1923. The frequencies were accurate to "better than three-tenths of one percent." At first, the transmitter had to be manually switched from one frequency to the next, using a wavemeter. The first quartz oscillators

Crystal oscillator

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...

were invented in the mid-1920s, and they greatly improved the accuracy of WWV's frequency broadcasts.

In 1926, WWV was nearly shut down. Its signal could only cover the eastern half of the United States, and other stations located in Minneapolis and at Stanford University

Stanford University

The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...

and the Massachusetts Institute of Technology

Massachusetts Institute of Technology

The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...

were slowly making WWV redundant. The station's impending shutdown was announced in 1926, but it was saved by a flood of protests from citizens who relied on the service. Later, in 1931, WWV underwent an upgrade. Its transmitter, now directly controlled by a quartz oscillator, was moved to College Park, Maryland

College Park, Maryland

College Park is a city in Prince George's County, Maryland, USA. The population was 30,413 at the 2010 census. It is best known as the home of the University of Maryland, College Park, and since 1994 the city has also been home to the "Archives II" facility of the U.S...

. Broadcasts began on 5 MHz. A year later, the station was moved again, to Department of Agriculture land in Beltsville, Maryland

Beltsville, Maryland

Beltsville is a census-designated place in northern Prince George's County, Maryland, United States. The population was 15,691 at the 2000 census. Beltsville includes the unincorporated community of Vansville.-Geography:...

, where it would stay until 1966. Broadcasts were added on 10 and 15 MHz, power was increased, and time signals, an A440

A440 (Concert A)

A440 is the musical note A above middle C. It has a frequency of 440 Hz and serves as a general tuning standard for musical pitch.Prior to the standardization on 440 Hz, many countries and organizations followed the Austrian government's 1885 recommendation of 435 Hz...

tone, and ionosphere reports were all added to the broadcast in June 1937.

WWV was nearly destroyed by a fire on November 6, 1940. The frequency and transmitting equipment was recovered, and the station was back on the air (with reduced power) on November 11. Congress funded a new station in July 1941, and it was built 5 kilometres (3.1 mi) south of the former location. WWV resumed normal broadcasts on 2.5, 5, 10, and 15 MHz on August 1, 1943.

Time signals

WWV had been broadcasting second pulses since 1937, but these pulses were not tied to actual time. In June 1944, the United States Naval Observatory

United States Naval Observatory

The United States Naval Observatory is one of the oldest scientific agencies in the United States, with a primary mission to produce Positioning, Navigation, and Timing for the U.S. Navy and the U.S. Department of Defense...

allowed WWV to use the USNO's clock as a source for its time signals. Over a year later, in October 1945, WWV broadcast Morse code

Morse code

time announcements every five minutes. Voice announcements started on January 1, 1950, and were broadcast every five minutes. Frequencies of 600 Hz and 440 Hz were broadcast during alternating minutes. By this time, WWV was broadcasting on 2.5, 5, 10, 15, 20, 25, 30, and 35 MHz. The 30 and 35 MHz broadcasts were ended in 1953.

A binary-coded decimal

Binary-coded decimal

In computing and electronic systems, binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by its own binary sequence. In BCD, a numeral is usually represented by four bits which, in general, represent the decimal range 0 through 9...

time code began testing in 1960, and became permanent in 1961. This "NASA time code" was modulated onto a 1000 Hz audio tone at 100 Hz, sounding somewhat like a monotonous repeated "baaga-bong". The code was also described as sounding like a "buzz-saw". On July 1, 1971, the time code's broadcast was changed to the present 100 Hz subcarrier, which is inaudible when using a normal radio (but can be heard using headphones or recorded using a chart recorder

Chart recorder

A chart recorder is an electromechanical device that records an electrical or mechanical input trend onto a piece of paper . Chart recorders may record several inputs using different color pens and may record onto strip charts or circular charts...

).

WWV moved to its present location at Fort Collins on December 1, 1966, enabling better reception of its signal throughout the continental United States. WWVB

WWVB

signed on in that location three years earlier. In April 1967, WWV stopped using the local time of the transmitter site (Eastern Time until 1966, and Mountain Time afterwards) and switched to Coordinated Universal Time

Coordinated Universal Time

Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

.

The 20 and 25 MHz broadcasts were discontinued in 1977, but the 20 MHz broadcast was reinstated the next year. The voice used on WWV was that of Don Elliott Heald

Don Elliott Heald

Don Elliot Heald graduated from University of Florida in 1947 and began his career at WRUF in Gainesville, Florida. He then took a news job at WSB radio and then moved to WSB-TV. Heald considered his 30 years at WSB as the "Golden Age" of television...

until August 13, 1991, when equipment changes required rerecording the announcer's voice. The one used at that time was that of John Doyle

John Doyle (announcer)

John Doyle is a professional announcer whose voice was most notably used by the National Institute of Standards and Technology on their radio clock WWV, a "time and temperature" voice for the Audichron Company.and others....

, but was soon switched to the voice of KSFO morning host Lee Rodgers.

The radio signals of WWV, WWVB and WWVH, along with the atomic clocks that their time signals derive from, are maintained by NIST's Time and Frequency Division, which is based in nearby Boulder, Colorado

Boulder, Colorado

. The Time and Frequency Division is part of the NIST's Physics Laboratory, based in Gaithersburg, Maryland

Gaithersburg, Maryland

Gaithersburg is a city in Montgomery County, Maryland, United States. The city had a population of 59,933 at the 2010 census, making it the fourth largest incorporated city in the state, behind Baltimore, Frederick, and Rockville...

. NIST's predecessor, the National Bureau of Standards, previously maintained WWV as a part of the Department of Agriculture

United States Department of Agriculture

; NIST is currently part of the Department of Commerce

United States Department of Commerce

The United States Department of Commerce is the Cabinet department of the United States government concerned with promoting economic growth. It was originally created as the United States Department of Commerce and Labor on February 14, 1903...

WWV and Sputnik

WWV's 20 MHz signal was used for a unique purpose in 1958: to track the disintegration of Russian satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

Sputnik I after the craft's onboard electronics failed. Dr. John D. Kraus

John D. Kraus

John Daniel Kraus was an American physicist known for his contributions to electromagnetics, radio astronomy, and antenna theory. His inventions included the helical antenna, the corner reflector, and several other types of antennas...

, a professor at The Ohio State University, knew that a meteor entering the upper atmosphere leaves in its wake a small amount of ionized air. This air reflects a stray radio signal back to Earth, strengthening the signal at the surface for a few seconds. This effect is known as meteor scatter. Dr. Kraus figured that what was left of Sputnik would exhibit the same effect, but on a larger scale. His prediction was correct; WWV's signal was noticeably strengthened for durations lasting over a minute. In addition, the strengthening came from a direction and at a time of day that agreed with predictions of the paths of Sputnik's last orbits. Using this information, Dr. Kraus was able to draw up a complete timeline of Sputnik's disintegration. In particular, he observed that satellites do not fail as one unit; instead, the spacecraft broke up into its component parts as it moved closer to Earth.

Call Sign

WWV is one of a small number of radio stations west of the Mississippi River

Mississippi River

The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

with a call sign

North American call sign

Call signs in North America are frequently still used by North American broadcast stations in addition to amateur radio and other international radio stations that continue to identify by call signs around the world...

beginning with W. The W call sign stems from the station's early locations in D.C. and Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

—the call sign was maintained when the federal government moved the station to Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

—and the fact that WWV, being a government station, does not fall within the FCC

Federal Communications Commission

The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...

's jurisdiction with respect to call sign

Call sign

In broadcasting and radio communications, a call sign is a unique designation for a transmitting station. In North America they are used as names for broadcasting stations...

s. However FCC regulations do dictate that time stations are to be issued call signs beginning with "WWV".

Broadcast format

On top of the standard carrier frequencies, WWV carries additional information using standard double-sideband amplitude modulation

Amplitude modulation

Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...

.
WWV's transmissions follow a regular pattern repeating each minute. They are coordinated with its sister station WWVH to limit interference between them. Because they are so similar, both are described here.

WWV/WWVH minute format
Second	WWV	WWVH
0–1	Minute beep (0.8 s)
1–45	Standard tone or voice announcement
45–52.5	Silence (except tick)	Voice time announcement
52.5–60	Voice time announcement	Silence (except tick)

Time of day

WWV transmits the exact time of day in two separate ways:

English-language voice announcements.
Binary time code, which also gives the date.

The transmitted time is given in Coordinated Universal Time

Coordinated Universal Time

(UTC).

Per-second ticks and minute markers

WWV transmits audio "ticks" once per second, to allow for accurate manual clock synchronization. These ticks are always transmitted, even during voice announcements and silent periods. Each tick begins on the second, lasts 5 ms and consists of 5 cycles of a 1000 Hz sine wave. To make the tick stand out more, all other signals are suppressed for 40 ms, from 10 ms before the second until 30 ms after (25 ms after the tick). As an exception, no tick (and no silent interval) is transmitted at 29 or 59 seconds past the minute. In the event of a leap second, no tick is transmitted during second 60 of the minute, either.

On the minute, the tick is extended to a 0.8 second long beep, followed by 0.2 s of silence. On the hour, this minute pulse is transmitted at 1500 Hz rather than 1000. The beginning of the tone corresponds to the start of the minute.

Between seconds one and sixteen inclusive past the minute, the current difference between UTC and UT1

Universal Time

Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...

is transmitted by doubling some of the once-per-second ticks, transmitting a second tick 100 ms after the first. (The second tick preempts other transmissions, but does not get a silent zone.) The absolute value of this difference, in tenths of a second, is determined by the number of doubled ticks. The sign is determined by the position: If the doubled ticks begin at second one, UT1 is ahead of UTC; if they begin at second nine, UT1 is behind UTC.

WWVH transmits similar 5 ms ticks, but they are sent as 6 cycles of 1200 Hz. The minute beep is also 1200 Hz, except on the hour when it is 1500 Hz.

The ticks and minute tones are transmitted at 100% modulation (0 dBFS

DBFS

Decibels relative to full scale, commonly abbreviated dBFS, measures decibel amplitude levels in digital systems such as pulse-code modulation which have a defined maximum available peak level....

Voice time announcements

Voice announcements of time of day are made at the end of every minute, giving the time of the following minute beep. The format for the voice announcement is, "At the tone, X hours, Y minute(s), Coordinated Universal Time."
The announcement is in a male voice and begins 7.5 seconds before the minute tone.

WWVH makes an identical time announcement, starting 15 seconds before the minute tone, in a female voice.

When voice announcements were first instituted, they were phrased as follows: "National Bureau of Standards, WWV; when the tone returns, [time] Eastern Standard Time." After the 1967 switch to UTC, the announcement changed to "National Bureau of Standards, WWV, Fort Collins, Colorado; next tone begins at X hours, Y minute(s), Greenwich Mean Time." However, this format would be short-lived. The announcement was changed again to the current format in 1971.

Voice time announcements are sent at 75% modulation, i.e. the carrier varies between 25% and 175% of nominal power.

Standard frequencies

WWV and WWVH transmit 44 seconds of audio tone in most minutes. It begins after the 1-second minute mark and continues until the beginning of the WWVH time announcement 45 seconds after the minute.

Even minutes (except for minute 2) transmit 500 Hz, while 600 Hz is heard during odd minutes. The tone is interrupted for 40 ms each second by the second ticks. WWVH is similar, but exchanges the two tones: 600 Hz during even minutes and 500 Hz during odd.

WWV also transmits a 440 Hz tone, a pitch

Pitch (music)

Pitch is an auditory perceptual property that allows the ordering of sounds on a frequency-related scale.Pitches are compared as "higher" and "lower" in the sense associated with musical melodies,...

commonly used in music (A440

A440 (Concert A)

, the note A above middle C

Middle C

C or Do is the first note of the fixed-Do solfège scale. Its enharmonic is B.-Middle C:Middle C is designated C4 in scientific pitch notation because of the note's position as the fourth C key on a standard 88-key piano keyboard...

) during minute :02 of each hour, except for the first hour of the UTC day. Since the 440 Hz tone is only transmitted once per hour, many chart recorder

Chart recorder

s may use this tone to mark off each hour of the day, and likewise, the omission of the 440 Hz tone once per day can be used to mark off each twenty-four hour period. WWVH transmits the same tone during minute :01 of each hour.

No tone is transmitted during voice announcements from either WWV or WWVH; the latter causes WWV to transmit no tone during minutes :43–:51 (inclusive) and minutes :29 and :59 of each hour. Likewise, WWVH transmits no tone during minutes :00, :30, :08–:10 and :14–:19.

Audio tones and other voice announcements are sent at 50% modulation.

Other voice announcements

WWV transmits the following 44-second voice announcements (in lieu of the standard frequency tones) on an hourly schedule:

A station identification at :00 and :30 past each hour;
marine storm warnings, provided by the National Weather Service
National Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...

, for the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

at :08 and :09 minutes past, and for the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

at :10 past;
at :14 and :15 past, GPS satellite health reports
Notice Advisory to NAVSTAR Users
A notice advisory to NAVSTAR users, or NANU, is a message issued jointly by the United States Coast Guard and the GPS Operations Center at Schriever Air Force Base in Colorado. NANUs provide updates on the general health of individual satellites in the GPS constellation...

from the Coast Guard
United States Coast Guard
The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...

Navigation Center;
at :18 past, a special "geophysical alert" report from NOAA
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

is transmitted, containing information on solar activity and shortwave radio propagation conditions. These particular alerts were to be discontinued on September 6, 2011. However, as of June 17, 2011, WWV is announcing at :18 past that the decision has been retracted and that the geophysical alert reports "will continue for the forseeable future".

Additional time slots are normally transmitted as a standard frequency tone, but can be preempted by voice messages if necessary:

At :04 and :16 past the hour, NIST broadcasts any announcements regarding a manual change in the operation of WWV and WWVH, such as leap second announcements. These minutes are marked in the broadcast schedule as "NIST Reserved". When not used, a 500 Hz tone is broadcast.
Minute 11 is used for additional storm warnings if necessary. If not, a 600 Hz tone is transmitted.

WWVH transmits the same information on a different schedule. Also, its storm warnings cover the area around the Hawaiian islands rather than North America.

WWV/WWVH hourly schedule
Second ticks are transmitted over top of signals listed here.
Minute	\| WWV	\| WWVH	Minute	WWV	WWVH	Minute	WWV	WWVH
00	Station identification	Silence	20	500 Hz	600 Hz	40	500 Hz	600 Hz
01	600 Hz	440 Hz	21	600 Hz	500 Hz	41	600 Hz	500 Hz
02	440 Hz	600 Hz	22	500 Hz	600 Hz	42	500 Hz	600 Hz
03	600 Hz	(NIST reserved)	23	600 Hz	500 Hz	43	Silence	GPS status
04	(NIST reserved)	600 Hz	24	500 Hz	600 Hz	44	Silence	GPS status
05	600 Hz	500 Hz	25	600 Hz	500 Hz	45	Silence	Geophysical alerts
06	500 Hz	600 Hz	26	500 Hz	600 Hz	46	Silence	600 Hz
07	600 Hz	500 Hz	27	600 Hz	500 Hz	47	Silence	(NIST reserved)
08	North Atlantic storm warnings	Silence	28	500 Hz	600 Hz	48	Silence	West Pacific storm warnings
09	North Atlantic storm warnings	Silence	29	Silence	Station identification	49	Silence	East Pacific storm warnings
10	Northeast Pacific storm warnings	Silence	30	Station identification	Silence	50	Silence	South Pacific storm warnings
11	(Additional storm warnings)	Silence	31	600 Hz	500 Hz	51	Silence	North Pacific storm warnings
12	500 Hz	600 Hz	32	500 Hz	600 Hz	52	Silence	(Additional storm warnings)
13	600 Hz	500 Hz	33	600 Hz	500 Hz	53	600 Hz	500 Hz
14	GPS status	Silence	34	500 Hz	600 Hz	54	500 Hz	600 Hz
15	GPS status	Silence	35	600 Hz	500 Hz	55	600 Hz	500 Hz
16	(NIST reserved)	Silence	36	500 Hz	600 Hz	56	500 Hz	600 Hz
17	600 Hz	Silence	37	600 Hz	500 Hz	57	600 Hz	500 Hz
18	Geo-alerts discontinuation notice	Silence	38	500 Hz	600 Hz	58	500 Hz	600 Hz
19	Geophysical alerts	Silence	39	600 Hz	500 Hz	59	Silence	Station identification

Digital time code

Time of day is also continuously transmitted using a digital time code

Time code

A timecode is a sequence of numeric codes generated at regular intervals by a timing system.- Video and film timecode :...

, interpretable by radio-controlled clocks

Radio clock

A radio clock or radio-controlled clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock...

. The time code uses a 100 Hz subcarrier

Subcarrier

A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...

of the main signal. That is, it is an additional low-level 100 Hz tone added to the other AM audio signals.

This code is similar to, and has the same framework as, the IRIG H time code and the time code that WWVB

WWVB

transmits, except the individual fields of the code are rearranged and are transmitted with the least significant bit sent first.
Like the IRIG timecode, the time transmitted is the time of the start of the minute.
Also like the IRIG timecode, numeric data (minute, hour, day of year, and last two digits of year) are sent in binary-coded decimal

Binary-coded decimal

(BCD) format rather than as simple binary integers:
Each decimal digit is sent as two, three, or four bits (depending on its possible range of values).

Bit encoding

The 100 Hz subcarrier is transmitted at −15 dBFS (18% modulation) beginning at 30 ms from the start of the second (the first 30 ms are reserved for the seconds tick), and then reduced by 15 dB (to −30 dBFS, 3% modulation) at one of three times within the second.
The duration of the high amplitude 100 Hz subcarrier encodes a data bit of 0, a data bit of 1, or a "marker", as follows:

If the subcarrier is reduced 800 ms past the second, this indicates a "marker."
If the subcarrier is reduced 500 ms past the second, this indicates a data bit with value one.
If the subcarrier is reduced 200 ms past the second, this indicates a data bit with value zero.

A single bit

Bit

A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

or marker is sent in this way in every second of each minute except the first (second :00). The first second of each minute is reserved for the minute marker, previously described.

In the diagram above, the red and yellow bars indicate the presence of the 100 Hz subcarrier,
with yellow representing the higher strength subcarrier (−15 dB referenced to 100% modulation)
and red the lower strength subcarrier (−30 dB referenced to 100% modulation).
The widest yellow bars represent the markers,
the narrowest represent data bits with value 0,
and those of intermediate width represent data bits with value 1.

Interpretation

It takes one minute to transmit a complete time code.
Most of the bits encode UTC time, day of year, year of century, and UT1 correction up to ±0.7 s.

Like the WWVB time code, only the tens and units digits of the year are transmitted;
unlike the WWVB time code, there is no direct indication for leap year.
Thus, receivers assuming that year 00 is a leap year (correct for year 2000) will be incorrect in the year 2100.
On the other hand, receivers that assume year 00 is not a leap year will be correct for 2001 through 2399.

The table below shows the interpretation of each bit, with the "Ex" column being the values from the example above.

WWV BCD time code
Bit	Weight	Meaning	Ex	Bit	Weight	Meaning	Ex	Bit	Weight	Meaning	Ex
:00	No 100 Hz (minute mark)			:20	1	Hours Example: 21	1	:40	100	Day of year (cont.)	0
:01	0	Unused, always 0.	0	:21	2		0	:41	200	Day of year (cont.)	0
:02	DST1	DST in effect at 00:00Z today	0	:22	4		0	:42	0	Unused, always 0.	0
:03	LSW	Leap second at end of month	0	:23	8		0	:43	0		0
:04	1	Units digit of year Example: 9	1	:24	0		0	:44	0		0
:05	2		0	:25	10		0	:45	0		0
:06	4		0	:26	20		1	:46	0		0
:07	8		1	:27	0	Unused, always 0.	0	:47	0		0
:08	0	Unused, always 0.	0	:28	0	Unused, always 0.	0	:48	0		0
:09	P1	Marker	M	:29	P3	Marker	M	:49	P5	Marker	M
:10	1	Minutes Example: 30	0	:30	1	Day of year Ordinal date An ordinal date is a calendar date typically consisting of a year and a day of year ranging between 1 and 366 , though year may sometimes be omitted... 1=January 1 365=December 31 (366 if a leap year) Example: 86 (March 27)	0	:50	+	DUT1 DUT1 The time correction DUT1 is the difference between Universal Time , which is defined by Earth's rotation, and Coordinated Universal Time , which is defined by a network of precision clocks.... sign (1=positive)	1
:11	2		0	:31	2		1	:51	10	Tens digit of year Example: 0	0
:12	4		0	:32	4		1	:52	20		0
:13	8		0	:33	8		0	:53	40		0
:14	0		0	:34	0		0	:54	80		0
:15	10		1	:35	10		0	:55	DST2	DST in effect at 24:00Z today	0
:16	20		1	:36	20		0	:56	0.1	DUT1 magnitude (0 to 0.7 s). DUT1 = UT1−UTC. Example: 0.3 s	1
:17	40		0	:37	40		0	:57	0.2		1
:18	0	Unused, always 0.	0	:38	80		1	:58	0.4		0
:19	P2	Marker	M	:39	P4	Marker	M	:59	P0	Marker	M

The example shown encodes day 86 (March 27) of 2009, at 21:30:00 UTC. DUT1 is +0.3, so UT1 is 21:30:00.3.
Daylight Saving Time was not in effect at the previous 00:00 UTC (DST1=0), and will not be in effect at the next 00:00 UTC (DST2=0).
There is no leap second scheduled (LSW=0).

Daylight saving time and leap seconds

The time code contains three bits announcing daylight saving time

Daylight saving time

Daylight saving time —also summer time in several countries including in British English and European official terminology —is the practice of temporarily advancing clocks during the summertime so that afternoons have more daylight and mornings have less...

(DST) changes and imminent leap second

Leap second

A leap second is a positive or negative one-second adjustment to the Coordinated Universal Time time scale that keeps it close to mean solar time. UTC, which is used as the basis for official time-of-day radio broadcasts for civil time, is maintained using extremely precise atomic clocks...

Bit :03 is set near the beginning of the month which is scheduled to end in a leap second. It is cleared when the leap second occurs.
Bit :55 (DST2) is set at UTC midnight just before DST comes into effect. It is cleared at UTC midnight just before standard time resumes.
Bit :02 (DST1) is set at UTC midnight just after DST comes into effect, and cleared at UTC midnight just after standard time resumes.

If the DST1 and DST2 bits differ, DST is changing during the current UTC day, at the next 02:00 local time. Before the next 02:00 local time after that, the bits will be the same. Each change in the DST bits happens at 00:00 UTC and so will first be received in the mainland United States between 16:00 (PST) and 20:00 (EDT), depending on local time zone and on whether DST is about to begin or end. A receiver in the Eastern time zone (UTC-5) must therefore correctly receive the "DST is changing" indication within a seven hour period before DST begins, and six hours before DST ends, if it is to change the local time display at the correct time. Receivers in the Central, Mountain, and Pacific time zones have one, two, and three more hours of advance notice, respectively.

During a leap second, a binary zero is transmitted in the time code; in this case, the minute will not be preceded by a marker.

Levels of modulation

The once-per-second "ticks" and minute and hour tones are modulated onto the carrier signal at 100 percent, or 0 dBc

DBc

dBc is the power ratio of a signal to a carrier signal, expressed in decibels. For example, phase noise is expressed in dBc/Hz at a given frequency offset from the carrier...

. The time code and audio tones are modulated at 50 percent, or approximately −3 dBc, and the maximum modulation level for the voice recordings is 75 percent, or approximately −1.25 dBc.

Transmission system

WWV broadcasts its signal on five transmitters, one per frequency. The transmitters for 2.5 MHz and 20 MHz put out an ERP

Effective radiated power

In radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...

of 2.5 kW, while those for the other three frequencies use 10 kW of ERP.

Each transmitter is connected to a dedicated antenna

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

, which has a height corresponding to approximately one-half of its signal's wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

, and the signal radiation patterns from each antenna are omnidirectional. The top half of each antenna tower contains a quarter-wavelength radiating element, and the bottom half uses nine guy wires

Guy-wire

A guy-wire or guy-rope, also known as simply a guy, is a tensioned cable designed to add stability to structures . One end of the cable is attached to the structure, and the other is anchored to the ground at a distance from the structure's base...

, connected to the midpoint of the tower and sloped at one-to-one from the ground—with a length of

\tfrac{\sqrt{2}\lambda}{4}

—as additional radiating elements.

Half-hourly station identification announcement

WWV identifies itself twice each hour, at 0 and 30 minutes past the hour. The text of the identification is as follows:

WWV accepts reception reports sent to the address mentioned in the station ID, and responds with QSL

QSL

QSL is one of the Q codes used in radiocommunication and radio broadcasting. A Q code message can stand for a statement or a question . In this case, QSL? means "do you confirm receipt of my transmission?" while QSL means "I confirm receipt of your transmission". Some also take it to mean "Query...

cards.

Telephone service

WWV's time signal can also be accessed by telephone by calling +1-303-499-7111. Telephone calls are limited to two minutes in length, and the signal is delayed by an average of 30 milliseconds.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.