WWV (radio station)
WWV is the callsign of the National Institute of Standards and Technology {NIST} shortwave radio station located in Fort Collins, Colorado, United States. 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.
History
Launch
WWV is the oldest continuously-operating radio station in the United States, first going on the air from Washington, D.C. in May 1920, approximately six months before the launch of KDKA. The station first broadcast Friday evening concerts on 600 kHz, and it could be heard 40 kilometres (25 mi) from Washington. On December 15, 1920, it began broadcasting on 750 kHz, distributing Morse code news reports from the Department of Agriculture. This signal could be heard up to 300 kilometres (190 mi) from Washington. These news broadcasts ended on April 15, 1921.[1]
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 close to their assigned frequencies. Testing began on January 29, 1923, and frequencies from 200 to 545 kHz were broadcast. In March 1923, WWV was broadcasting frequencies from 125 to 2000 kHz. 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 were invented in the mid-1920s, and they greatly improved the accuracy of WWV's frequency broadcasts.[1]
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 and the Massachusetts Institute of Technology 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. Broadcasts began on 5 MHz. A year later, the station was moved again, to Department of Agriculture land in Beltsville, Maryland, where it would stay until 1966. Broadcasts were added on 10 and 15 MHz, power was increased, and time signals, an A440 tone, and ionosphere reports were all added to the broadcast in June 1937. [1]
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 in January 1943.[1]
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 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 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. [1]
A binary-coded decimal 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". On July 1, 1971, the time code's broadcast was changed to the present 100 Hz subcarrier, which is inaudible.[1]
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 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.[1]
The 20 and 25 MHz broadcasts were discontinued in 1977, but the 20 MHz broadcast was reinstated the next year.[1] 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 was soon switched to the voice of KSFO morning host Lee Rodgers.[2]
Callsign
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".[3]
Broadcast format
Time of day
WWV transmits the exact time of day using two simultaneous, but separate, methods. The transmitted time is given in Coordinated Universal Time (UTC).
Voice announcements
Voice announcements of time of day are made every minute and followed by a long beep that serves as the "on-time marker" for each announcement. The format for the voice announcement is, "At the tone, X hours, Y minute(s), Coordinated Universal Time." The announcement is followed by a long beep, marking the beginning of the minute that was just announced. These long beeps are also used to mark off standard intervals of one minute, and are usually tones of 1000 Hz, except for the top of the hour, when a 1500 Hz tone is used. The announcement is in a male voice and begins 7.5 seconds before the end of the current minute. [4]
When voice announcements were first instituted, they were phrased as follows: "National Bureau of Standards, WWV; when the tone returns, [time] Eastern Standard Time."[5] 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." The current voice announcement was instituted after the 1991 re-recording.[6]
BCD time code
Time of day is also continuously transmitted using a sub-audible digital time code, interpretable by radio-controlled clocks. The time code 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 start of the most recent long beep as its "on-time marker." This code is broadcast in binary-coded decimal format on a 100 Hz subcarrier of the main signal. One minute is required to make one complete transmission. During a leap second, a binary zero is transmitted in the time code.[7] This code is similar to, and has the same framework as, the time code that WWVB transmits, except the individual elements of the code are rearranged and are transmitted with the least significant bit sent first.
Standard time intervals
WWV transmits audio "ticks" once per 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 clock synchronization. These ticks are always transmitted, even during voice announcements and silent periods. Each tick lasts 5 ms and consists of 5 cycles of a 1000 Hz sine wave. A silent zone extending from 10 ms before each tick to 20 ms after makes it easier for the tick to be heard. 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. [4]
Standard frequencies
In most minutes of the hour, WWV transmits standard audio frequencies of 500 and 600 Hz, switching between the two frequencies each minute. The 500 Hz tones occur in the even-numbered minutes (except for minute 2), and the 600 Hz tones are heard in the odd minutes. These two frequencies are used to synchronize 50 Hz and 60 Hz electrical power supplies respectively. WWV also transmits a 440 Hz tone (a pitch commonly used in music for the note A above middle C, A440) in the second minute 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 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. No audio tones are transmitted from WWV between 43 and 51 minutes inclusive past the hour. [4]
Other information
WWV's broadcasts are not limited to time of day and standard time intervals. Marine storm warnings, provided by the National Weather Service, are broadcast for the Atlantic Ocean at 8 and 9 minutes past, and for the Pacific Ocean at 10 minutes past. At 14 and 15 minutes past the hour, GPS satellite health reports from the Coast Guard are transmitted. And at 18 minutes past the hour, a special "geophysical alert" report from NOAA is transmitted, containing information on solar activity and shortwave radio propagation conditions. [4]
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. 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. [8]
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. [1]
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:
National Institute of Standards and Technology time: this is Radio Station WWV, Fort Collins Colorado, broadcasting on internationally allocated standard carrier frequencies of two-point-five, five, ten, fifteen, and twenty megahertz, providing time of day, standard time interval, and other related information. Inquiries regarding these transmissions may be directed to the National Institute of Standards and Technology, Radio Station WWV, 2000 East County Road 58, Fort Collins, Colorado, 80524.
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 +1-303-499-7111. Telephone calls are limited to two minutes in length, and the signal is delayed by an average of 30 milliseconds. [9]
References
- ^ a b c d e f g h i NIST Special Publication 250-67: NIST Time and Frequency Stations: WWV, WWVH and WWVB
- ^ DX Listening Digest 5-016 "For a short time, a broadcaster from Atlanta named John Doyle's voice was used on the broadcast; the voice announcement was then re-recorded by a radio personality in the San Francisco area named Lee Rodgers." -Glenn Nelson, NIST
- ^ "Telecommunication: Frequency allocations and radio treaty matters, general rules and regulations § 2.302" (PDF). Federal Communications Commission. Retrieved 2009-10-24.
- ^ a b c d Information Transmitted by WWV and WWVH
- ^ NBS Letter Circular 1023: 1956 Guide to NBS Time and Frequency Services
- ^ "NBS Special Publication 236: 1968 Guide to NBS Time and Frequency Services" (PDF). National Institute of Standards and Technology. Retrieved 2009-10-24.
- ^ Lombardi, Michael (2002). "NIST Time and Frequency Services (NIST Special Publication 432)" (PDF). NIST. p. 80. Retrieved 2009-04-12.
- ^ NIST Radio Station WWV
- ^ NIST. "NIST Telephone Time-of-Day Service". Retrieved 2008-07-06.