WWV (radio station)

WWV is the callsign of NIST's shortwave radio station located in Fort Collins, Colorado. WWV's main function is the continuous dissemination of official U.S. Government time signals. The station broadcasts simultaneously on five distinct frequencies: 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. These carrier frequencies, as well as the time signals, are derived from a set of atomic clocks located at the transmitter site, which themselves are traceable to NIST's primary frequency standard in Boulder, Colorado using such techniques as GPS common view observations. WWV is partnered with radio station WWVH, located in Hawaii. Onsite with WWV in Fort Collins is also radio station WWVB, which operates on the low frequency of 60 kHz.

WWV is the oldest continuously-operating radio station in the United States, first going on the air from Washington, D.C. in May of 1920, approximately six months before the launch of KDKA. The station was formerly located in Greenbelt, Maryland, on land which now is part of NASA's Goddard Space Flight Center. WWV moved to its present location at Fort Collins on December 1, 1966, enabling better reception of its signal throughout the continental United States.

WWV is one of a small number of radio stations west of the Mississippi River with a call sign beginning with W. The W callsign stems from the station's early locations in D.C. and Maryland—the callsign was maintained when the federal government moved the station to Colorado—and the fact that WWV, being a government station, does not fall within the FCC's jurisdiction with respect to call signs. However FCC regulations do dictate that time stations are to be issued call signs beginning with "WWV". [47 CFR §2.302, [http://a257.g.akamaitech.net/7/257/2422/12feb20041500/edocket.access.gpo.gov/cfr_2004/octqtr/47cfr2.302.htm a257.g.akamaitech.net/7/257/2422/12feb20041500/edocket.access.gpo.gov/cfr_2004/octqtr/47cfr2.302.htm] , via [http://www.access.gpo.gov/nara/cfr/waisidx_04/47cfr2_04.html www.access.gpo.gov/nara/cfr/waisidx_04/47cfr2_04.html] .]

Broadcast format

WWV transmits the exact time of day in two ways at the same time. The first method is through voice announcements made every minute, each followed by a long beep that serves as the "on-time marker" for each announcement. These long beeps are also used to mark off standard intervals of one minute, and are usually tones of , except for the top of the hour, when a tone is used. The second method of transmitting the time of day is through a continuously-transmitted sub-audible digital time code, which also carries extra information such as whether or not Daylight Saving Time is in effect, and when the next leap second will occur. The time code is based on the "H" format of IRIG time code, and uses the most recent long beep as its "on-time marker." The voice announcements are made in a male voice to distinguish them from those of WWVH in Hawaii. The voice used on WWV was that of Don Elliott Heald until August 13, 1991, when equipment changes required rerecording the announcer's voice. The one used at that time was that of John Doyle, but complaints resulted in a switch to the voice of Lee Rodgers because it sounded more like Elliott's.. [ [http://ts.nist.gov/MeasurementServices/Calibrations/upload/SP250-67.pdf ts.nist.gov/MeasurementServices/Calibrations/upload/SP250-67.pdf] ] Verify credibility|date=July 2008 The voice announcements are useful for people manually setting clocks, while the digital time codes can be used by radio-controlled clocks. The transmitted time is given in Coordinated Universal Time (UTC). WWV also "ticks" each second (except at 29 and 59 seconds past the minute, the omissions used to encode the standard interval of thirty seconds), to allow for accurate manual synchronization. These ticks are always transmitted, even during voice announcements and silent periods. 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. The absolute value of this difference, in tenths of a second, is determined by the number of doubled ticks. If the doubled ticks are between seconds one and eight inclusive past the minute, UT1 is ahead of UTC. If the doubled ticks fall between seconds nine and sixteen inclusive, UT1 is behind UTC.

In most minutes of the hour, WWV transmits standard audio frequencies of and , switching between the two frequencies each minute. (The 500 Hz tone occurs in minutes 0, 2, 4, …, and the 600 Hz tone in minutes 1, 3, 5, ….) These two frequencies are used to synchronize 50 Hz and 60 Hz electrical power supplies respectively. WWV also transmits a tone (a pitch commonly used in music for the note A above middle C) every hour at two minutes past, except for the first hour of the UTC day. Since the 440 Hz tone is only transmitted once per hour, many chart recorders 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.

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

WWV's broadcasts are not limited to time of day and standard time intervals. At 8, 9 and 10 minutes past the hour, WWV stops transmitting its standard audio signals (except for the ticks and time code) to broadcast regular high-seas weather warnings. At 14 and 15 minutes past the hour, GPS satellite health reports are transmitted. And at 18 minutes past the hour, a special "geophysical alert" report is transmitted, containing information on solar activity and shortwave radio propagation conditions. No audio tones are transmitted from WWV between 43 and 51 minutes inclusive past the hour.

Between 1945 and 1971, WWV transmitted an ID and the time of day in Morse code. During that time, the standard audio signals alternated between 440 Hz and 600 Hz, instead of the 500 and 600 Hz signals used today. Voice announcements of the time of day began on WWV in 1950. Before 1967, WWV's time of day announcements were in local time of the transmitter site. During the 1960s and 1970s, WWV also transmitted a 36-bit "NASA time code", supposedly for synchronizing naval clocks, for several minutes each hour. The code was modulated onto a 1000 Hz audio tone at 100 Hz, sounding somewhat like a monotonous repeated "Baaga-Bong".

During a leap second, a binary zero is transmitted in the time code.

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 of 2.5 kW, while those for the other three frequencies use 10 kW of ERP. Each transmitter is connected to a dedicated antenna, which has a height corresponding to approximately one-half of its signal's wavelength, 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, connected to the midpoint of the tower and sloped at one-to-one from the ground—with a length of one-quarter wavelength times the square root of two—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 cards.

Telephone service

WWV's time signal can also be accessed by telephone by calling [phone]. Telephone calls are limited to two minutes in length, and the signal is delayed by an average of 30 milliseconds. [cite web|url=http://tf.nist.gov/stations/sig.html|title=NIST Telephone Time-of-Day Service|author=NIST|accessdate=2008-07-06]

References

External links

* [http://tf.nist.gov/stations/wwv.html WWV official site]
* [http://www.obscure-disk.com/AtTheTone/ MP3 samples of historic and modern WWV/WWVH output]
* [http://www.lownoiserecords.com/wwv.htm Parody of WWV's broadcasts] - "The Tick" by Douglas Grant / LowNoise Productions
* [http://tf.nist.gov/timefreq/general/pdf/1969.pdf NIST Special Publication 250-67: NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB]
* [http://www.youtube.com/watch?v=94t4d-PlyAg Interview with the two voices of the speaking clock] From YouTube