WWV (radio station)

thumb|upright=1.3|WWV Transmitter Building (2002 or earlier)

thumb|WWV's 15 MHz antenna

WWV is a shortwave ("high frequency" or HF) radio station, located near Fort Collins, Colorado. It has broadcast a continuous time signal since 1945, and implements United States government frequency standards, with transmitters operating on 2.5, 5, 10, 15, 20, and 25 MHz. WWV is operated by the U.S. National Institute of Standards and Technology (NIST), under the oversight of its Time and Frequency Division, which is part of NIST's Physical Measurement Laboratory based in Gaithersburg, Maryland. The letters WWV are only a call sign and do not stand for anything (see below).

WWV was established in 1919 by the Bureau of Standards in Washington, D.C., making it one of the oldest continuously-operating radio stations in the United States. NIST celebrated WWV's centennial on October 1, 2019.

In 1931, the station relocated to the first of three suburban Maryland sites, before moving to a location near Fort Collins in 1966. WWV shares this site with longwave (also known as "low frequency" or LF) station WWVB, which transmits carrier and time code (no voice) at 60 kHz. NIST also operates shortwave station WWVH on Kauai, Hawaii. Both WWV and WWVH announce the time of day each minute in Coordinated Universal Time, and make other recorded announcements of general interest on an hourly schedule, including the Global Positioning System (GPS) satellite constellation status. Because they simultaneously transmit on the same frequencies, WWV uses a male voice in order to differentiate itself from WWVH, which uses a female voice.

Service

Since 1945, WWV has disseminated "official U.S. time" provided by government entities NIST and the United States Naval Observatory (USNO), to ensure that uniform time is maintained throughout the United States and around the world. WWV provides a public service by making time information freely available at all hours.

The time signals generated by WWV allow time-keeping devices such as radio-controlled clocks, weather stations and wristwatches to automatically maintain accurate time without the need for manual adjustment. These time signals are used by commercial and institutional interests where accurate time plays a vital role in daily operations including shipping, transport, technology, research, education, military, public safety and telecommunications. It is of particular importance in broadcasting, whether it be commercial, public, or private interests such as amateur radio operators, who use the station's transmissions to test their equipment.

Transmission system

{| class="wikitable"

! colspan=2 | WWV antenna coordinates (WGS84)

| 2.5 MHz ||

| 5 MHz ||

| 10 MHz ||

| 15 MHz ||

| 20 MHz ||

| 25 MHz ||

</div>

WWV broadcasts over six transmitters, each one dedicated to a single frequency. The transmitting frequencies and time signals of WWV, WWVB and WWVH, along with the four atomic (cesium) clocks from which their time signals are derived, are maintained by NIST's Time and Frequency Division, which is based in nearby Boulder, Colorado. The broadcast time is accurate to within of UTC and of the national time standard. Each transmitter has a dedicated antenna, with a height corresponding to one-half of its wavelength, and an omnidirectional signal radiation pattern. The top half of each antenna tower has a quarter-wavelength radiating element, and the bottom half uses nine guy wires, connected to the midpoint of the tower and sloped at one-to-one from the ground—with a length of times the wavelength—as additional radiating elements.

Telephone service

WWV's time signal can be accessed by telephone by calling +1 (303) 499-7111 (WWV). Telephone calls are limited to 2 minutes, and the signal is delayed by an average of 30 milliseconds due to telephone network propagation time.

History

Establishment

thumb|right|Alongside weekly broadcasts over WWV, in May 1920 the Bureau of Standards presented the "portaphone", with which one could "receive wireless impulses in the form of signals, music or speech, reproducing the same through a loud-speaking telephone and horn".

The earliest formal record of WWV's existence is in the October 1, 1919 issue of the Department of Commerce's Radio Service Bulletin, where it was listed as a new "experimental station" assigned to the Bureau of Standards in Washington, D.C., with the randomly issued call letters of WWV. However, there were also earlier reports of radio demonstrations by the Bureau, starting the previous February.

As of May 1920 the Bureau's Radio Laboratory was reported to be conducting weekly Friday evening concerts from 8:30 to 11:00, transmitting on 600 kHz. That same month, the Bureau demonstrated a portable radio receiver, called the "portaphone", which was said to be capable of receiving broadcast programs up to away. However, the station continued to make occasional broadcasts, and in January 1921 a new distance record was announced when a listener in Chattanooga, Tennessee reported hearing the "jazzy waves whirling out from the Bureau of Standards".

On December 15, 1920, WWV began broadcasting 500-word "Daily Radio Marketgrams", prepared by the U.S. Bureau of Markets, in Morse code on 750 kHz, which reportedly could be heard up to from Washington. However, on April 15, 1921 responsibility for the reports was transferred to four stations operated by the Post Office Department, including its WWX in Washington, D.C.

Standard frequency transmissions

At the end of 1922, WWV's purpose shifted to broadcasting standard frequency signals. These were an important aid to broadcasting and amateur stations, because their equipment limitations at the time meant they had difficulty staying on their assigned frequencies. Testing began on January 29, 1923. Regularly scheduled operations began on March 6, 1923, consisting of seven transmitting frequencies ranging from 550 to  kHz (wavelengths of 545 to 200 meters). 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 resonators (that stabilized the frequency generating oscillators) were invented in the mid-1920s, and they greatly improved the accuracy of WWV's frequency broadcasts.

WWV moved to a location near Fort Collins on December 1, 1966, enabling better reception of its signal throughout the continental United States. WWVB had 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 broadcasting Greenwich Mean Time or GMT. The station switched again, to Coordinated Universal Time (UTC), in 1974.

The voice used on WWV was that of professional broadcaster Don Elliott Heald until August 13, 1991, when equipment changes required re-recording the voice of another professional broadcaster, John Doyle, but was soon switched to the voice of KSFO morning host Lee Rodgers. Since then John Doyle's voice has been returned to the broadcast.

WWV, along with WWVB and WWVH, was recommended for defunding and elimination in NIST's Fiscal Year 2019 budget request. However, the final 2019 NIST budget preserved funding for the three stations.

WWV and Sputnik

WWV's 20 MHz signal was used for a unique purpose in 1958: to track the disintegration of Russian satellite Sputnik 1 after the craft's onboard electronics failed. John D. Kraus, a professor at 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. 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 a duration lasting over a minute. 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, Kraus was able to draw up a complete timeline of Sputnik's disintegration. In particular, he observed that satellites do not fall as one unit; instead, the spacecraft broke up into its component parts as it moved closer to Earth.

Broadcast format

On top of the standard carrier frequencies, WWV carries additional information using standard double-sideband amplitude modulation. WWV's transmissions follow a regular pattern repeating each minute; the pattern is coordinated with that of its sister station WWVH to limit interference between them. Because they are so similar, both are described here.

{|class="wikitable" style="text-align:center;"

|+ WWV/WWVH minute format

! Second!! WWV !! WWVH

| 0–1 ||colspan=2 style="background:#ffc"| Minute beep (0.8 s)

| 1–45 ||colspan=2 style="background:#cfc" | Standard tone or voice announcement

| 45–52.5 || Silence (except tick) ||style="background:#ccf"| Voice time announcement

| 52.5–60 ||style="background:#ccf"| Voice time announcement || Silence (except tick)

Date and time

WWV transmits the date and exact time as follows:

English-language voice announcements of time.
Binary-coded decimal time code of date and time, transmitted as varying length pulses of 100 Hz tone, one bit per second.

In both cases the transmitted time is given in Coordinated Universal Time (UTC).

Per-second ticks and minute markers

thumb|WWV seconds pulse generator, 1943

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  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  Hz rather than  Hz. 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 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. followed by 4-digit GMT sent in Morse code. After the 1967 switch to GMT, 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. "At the tone, X hour(s), Y minute(s), Greenwich Mean Time." The name "Greenwich Mean Time" was changed to "Coordinated Universal Time" in 1974.

Voice time announcements are sent at 75% modulation (−1.25 dBc), i.e., the carrier varies between 25% and 175% of nominal power. This signal began on 15 November 2021.

At :18 past, a special "geophysical alert" report from the National Oceanic and Atmospheric Administration is transmitted, containing information on solar activity and shortwave radio propagation conditions. Here is an example of this announcement from May 24, 2018 at 0905 UTC:
At :47 and :52, WWVH (only) broadcasts an announcement about the telephone time service.

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

At :10 past the hour WWV transmits a Department of Defense message if any exists; WWVH does the same at :50 past the hour.
:16 minutes past the hour is used for additional NIST announcements, if necessary.

WWVH transmits the same information on a different schedule. WWV and WWVH's voice announcements are timed to avoid crosstalk; WWV airs dead air when WWVH airs voice announcements, and vice versa.

Announcements formerly carried by WWV, but now discontinued, include:

Marine storm warnings, provided by the National Weather Service, for the Atlantic Ocean at :08 and :09 minutes past the hour, for the Pacific Ocean at :10 past, with :11 past available for additional warnings if necessary. WWVH's storm warnings were broadcast from :48 to :51, and covered the area around the Hawaiian islands and the Far East rather than North America. WWV and WWVH discontinued all weather content on February 7, 2019, and the time slots they previously occupied are now classified as "NIST Reserved."
At :14 and :15 past, GPS satellite health reports from the Coast Guard Navigation Center (:43 and :44 for WWVH).
Prior to the shutdown of the OMEGA navigation system in 1997, an OMEGA status report was broadcast at :16 past the hour.
There was a proposal to discontinue the geophysical alerts on September 6, 2011. However, as of June 17, 2011, WWV announced that the decision has been retracted and that the geophysical alert reports "will continue for the foreseeable future".

{|class="wikitable" style="text-align:center;"

|+ WWV/WWVH hourly schedule in this case, the minute will not be preceded by a marker.

{| class="wikitable" style="text-align:center;"

|+NIST Time Signal Station Services

!Station

!Year in service

!Year out of service

!Radio frequencies

!Audio frequencies

!Musical pitch

!Time intervals

!Time signals

!UT2 correction

!Propagation forecasts

!Geophysical alerts

|WWV

|1923

| rowspan="3" |

|✔

|WWVH

|1948

|✔

|WWVB

|1963

|✔

|WWVL