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NBS TIME AND FREQUENCY DISSEMINATION SERVICES Time and Frequency Division National Measurement Laboratory National Bureau of Standards Boulder, Colorado 80303 issued September 1979 FORWARD: This publication presents a description of the time and frequency dissemination services of the National Bureau of Standards. Those interested in information on the NBS atomic clock system, transmitting antennas, or discussion of technological applications of the dissemination services should refer to Section 9, OTHER PUBLICATIONS. This SPECIAL PUBLICATION 432 will be revised and reissued only as necessary to update information. INTRODUCTION The time and frequency community is a small community, generally unknown to the world at large, yet vitally important to many of the basic activities of everyday living. Electric power companies, radio and television stations, telephone companies, and navigators of ships and planes all depend heavily on precise frequency and time information. They must have a constantly available source - a reliable, nationally and internationally recognized STANDARD - with which to compare and regulate their own timing equipment. For over 55 years, the National Bureau of Standards (NBS) has been providing this standard for most users in the United States. Since the inception of the broadcast services from radio station WWV in 1923, NBS has continually improved and expanded its time and frequency dissemination services to meet the ever-growing needs of an ever-widening community of users. Today, still striving for better ways to serve its public, NBS is making major contributions to the nation's space and defense programs, to worldwide transportation and communications, and to a multitude of industrial operations, as well as providing convenient, highly accurate time service to many thousands of users throughout the world. Services are presently available from stations WWV and WWVB in Fort Collins, Colorado, and from WWVH in Kauai, Hawaii. In addition, services using network television and satellite signals are also available. This booklet is offered as a guide to these services. 1. WWV and WWVH NBS broadcasts continuous signals from its high-frequency radio stations WWV and WWVH. The radio frequencies used are 2.5, 5, 10 and 15 MHz. WWV also broadcasts on an additional frequency of 20 MHz. All frequencies carry the same program, but because of changes in ionospheric conditions, which sometimes adversely affect the signal transmissions, most receivers are not able to pick the signal on all frequencies at all times in all locations. Except during times of severe magnetic disturbances, however - which make all radio transmissions almost impossible - listeners should be able to receive the signal on at least one of the broadcast frequencies. As a general rule, frequencies above 10 MHz provide the best daytime reception while the lower frequencies are best for nighttime reception. Services provided by these stations include: Time announcements, Standard time intervals, Standard frequencies, Geophysical alerts, Marine storm warnings, Omega Navigation System status reports, UT1 time corrections, BCD time code Figure 1 gives the hourly broadcast schedules of these services along with station location, radiated power, and details of modulation. Figure 1 *** This section has been SLIGHTLY modified by KB9FRJ to adopt it more sufficiently to a text file presentation. The Hourly Broadcast Schedules of WWV and WWVH W W V B R O A D C A S T F O R M A T via telephone (303) 499-7111 Latitude: 40 degrees, 40 minutes, 49 seconds North Longitude: 105 degrees, 02 minutes, 27 seconds West NBS Radio Station WWV 2000 East County Rd 58 Fort Collins, CO 80524 Standard Broadcast Frequencies and Radiated Power: 2.5 MHz: 2500 Watts 5.0 MHz: 10000 Watts 10.0 MHz: 10000 Watts 15.0 MHz: 10000 Watts 20.0 MHz: 2500 Watts * BCD TIME CODE on 100 Hz Subcarrier * Beginning of each hour is identified by 0.8 sec long 1500Hz TONE * Beginning of each min. is identified by 0.8 sec long 1000Hz TONE * The 29th and 59th SECOND pulse of each minute is omitted Hourly Schedule Minutes after the top of the hour/Broadcast information 00 min Station Identification 02 min 440 Hz 1-HOUR mark 04 min reserved 08 min Storm information 09 min Storm information 10 min Storm information 16 min Omega reports 18 min Geo Alerts, Solar-terrestrial indices 30 min Station Identification In addition, minutes 45-50 have no audio tones so that storm forecasts from WWVH can be heard W W V H B R O A D C A S T F O R M A T via telephone (808) 335-4363 Latitude: 21 degrees, 59 minutes, 26 seconds North Longitude: 159 degrees, 46 minutes, 00 seconds West NBS Radio Station WWVH PO Box 417 Kekaha, Kauai, HI 96752 Standard Broadcast Frequencies and Radiated Power: 2.5 MHz: 5000 Watts 5.0 MHz: 10000 Watts 10.0 MHz: 10000 Watts 15.0 Mhz: 10000 Watts * BCD TIME CODE on 100 Hz Subcarrier * Beginning of each hour is identified by 0.8 sec long 1500Hz TONE * Beginning of each min. is identified by 0.8 sec long 1200Hz TONE * The 29th and 59th SECOND pulse of each minute is omitted Hourly Schedule Minutes after the top of the hour/Broadcast information 01 min 400 Hz 1-HOUR mark 03 min reserved 29 min Station Identification 47 min Omega reports 48 min Storm information 49 min Storm information 50 min Storm information 59 min Station Identification In addition, minutes 08-10 and minutes 15-19 have no audio tones so that informational broadcasts out of WWV can be heard. *** END figure 1 as edited by KB9FRJ for text file presentation *** 1a. Accuracy and Stability The time and frequency broadcasts are controlled by the primary NBS Frequency Standard in Boulder, Colorado. The frequencies as transmitted are accurate to within one part in 100 billion at all times. Deviations are normally less than one part in 1,000 billion from day to day. However, changes in the propagation medium (causing Doppler effect, diurnal shifts, etc.) result in fluctuations in the carrier frequencies as received by the user that may be very much greater than the uncertainty described above. 1b. Antennas and Modulation The broadcasts on 5, 10, and 15 MHz from WWVH are from phased vertical half-wave dipole arrays. They are designed and oriented to radiate a cardioid pattern directing maximum gain in a westerly direction. The 2.5 MHz antenna at WWVH and all antennas at WWV are half-wave dipoles that radiate omnidirectional patterns. At both WWV and WWVH, double sideband amplitude modulation is employed with 50 percent modulation on the steady tones, 25 percent for the BCD time code, 100 percent for the seconds pulses, and 75 percent for voice. 1c. Time Announcements Voice announcement are made from WWV and WWVH once every minute. To avoid confusion, a man's voice is used on WWV and a woman's voice on WWVH. The WWVH announcement occurs first - at 15 seconds before the minute - while the WWV announcement occurs at 7.5 seconds before the minute. Though the announcements occur at different times, the tone markers referred to are transmitted simultaneously from both stations. However, they may not be received at the same time due to propagation effects. The time referred to in the announcements is "Coordinated Universal Time" (UTC). It is coordinated through international agreements by the International Time Bureau (BIH) so that time signals broadcast from the many stations such as WWV throughout the world will be in close agreement. The specific hour and minute mentioned is actually the time at the time zone centered around Greenwich, England, and may be considered generally equivalent to the more well-known "Greenwich Mean Time" (GMT). UTC differs from your local time only by an integral number of hours. By knowing your local time zone and using the chart of world time zones in figure 3, the appropriate number of hours to add or subtract from UTC to obtain local time can be determined. The UTC time announcements are expressed in the 24-hour clock system -i.e., the hours are numbered beginning with 00 hours at midnight through 12 hours at noon to 23 hours, 59 minutes just before the next midnight. 1d. Standard Time Intervals The most frequent sounds hears on WWV and WWVH are the pulses that mark the seconds of each minutes, except for the 29th and 59th seconds pulses which are omitted completely. The first pulse of every HOUR is an 800-millisecond pulse of 1500 Hz. The first pulse of every minute is an 800-millisecond pulse of 1000 Hz at WWV and 1200 Hz at WWVH. The remaining seconds pulses are brief audio bursts (5 millisecond pulses) that resemble the ticking of a clock. All pulses commence at the beginning of each second. They are given by means of a double-sideband amplitude modulation. Each seconds pulse is preceded by 10 milliseconds of silence and followed by 25 milliseconds of silence to avoid interference which might make it difficult or impossible to pick out the seconds pulses. 1e. Standard Audio Frequencies In alternate minutes during most of each hour, 500 or 600 Hz audio tones are broadcast. A 440 Hz tone, the musical note A above middle C, is broadcast once each hour. In addition to being a musical standard, the 440 Hz tone can be used to provide an hourly marker for chart recorders or other automated devices. 1f. Official Announcements Forty-five-second announcement segments are available on a subscription basis to other Federal agencies to disseminate official and public service information. The accuracy and content of these announcement are the responsibility of the originating agency, not necessarily NBS. Most segments except those reserved for NBS use and the semi- silent periods are available. Arrangements for use of segments may be made through the Time and Frequencies Services Group, 524.06, National Bureau of Standards, Boulder, CO 80303. + Omega Navigation System Status Reports Omega Navigation System status reports are broadcast in voice from WWV at 16 minutes after the hour and from WWVH at 47 minutes after the hour. The international Omega Navigation System is a very low frequency (VLF) radio navigation aid operating in the 10 to 14 kHz frequency band. Eight stations are in operation around the world. Omega, like other radio navigation systems, is subject to signal degradation caused by ionospheric disturbances at high latitudes. The Omega announcements on WWV and WWVH are given to provide users with immediate notification of such events and other information on the status of the Omega system. For more information about the Omega Navigation System, contact Mr. David Scull, United States Coast Guard HQ, (G-ONSOD 43), Washington, DC 20590. + Geophysical Alerts Current geophysical alerts are broadcast in voice from WWV at 18 minutes after each hour. The messages are changed approximate every six hours at 1800, 0000, 0600, and 1300 UTC. Part A of the message gives the solar-terrestrial indices for the day; namely, the 1700Z solar flux from Ottawa, Canada at 2800 MHz, the estimated A value for Fredericksburg, Virginia, and the current, Boulder, Colorado, K-index. Part B gives the solar-terrestrial conditions for the previous 24 hours, and Part C gives the forecast for the next 24 hours. If stratwarm conditions exist, a brief advice is given at the end of the message. 1. Solar activity is classified as: VERY LOW Usually only quiet regions on the solar disk and no more than five of these; fewer than ten class-C subflares without centimetric radio burst of SID observed or expected. LOW Usually more than five but less than ten quiet regions on the solar disk; only class-C subflares without centimetric radio bursts or SID (sudden ionospheric disturbances) observed or expected. MODERATE Eruptive regions on the solar disk; fewer than five class-M X-ray events with centimetric radio bursts and SID observed or expected. HIGH Active regions on the solar disk; several class-M X-ray events with centimetric radio bursts and strong SID; and/or one to two importance=2 chromospheric flares or class-X X-ray events observed or expected. VERY HIGH Region capable of producing protons on the sun; one or more chromospheric flares of importance-2 or greater; with outstanding centimetric radio bursts (500 flux units or greater), Class-X X-ray bursts, and major SID observed or expected. 2. The geomagnetic field is classified as: QUIET A <= 7, usually no K-indices > 2 UNSETTLED 7 < A < 15 usually no K-indices > 3 ACTIVE 15 <= A < 30 a few K-indices of 4 3. The geomagnetic storms are classified as: MINOR 30 <= A < 50, K-indices mostly 4 and 5 MAJOR A > 50, some K-indices 6 or greater. Sudden commencements indicated by beginning time to nearest minute. Gradual commencement indicated by beginning time to nearest hour. 4. The rest of the report as follows: SOLAR FLARES CLASS C any solar X-ray burst with a peak flux at 1-8 angstroms of less than 1 microwatt per square meter CLASS M a solar X-ray burst with a peak flux at 1-8 angstroms, greater than or equal to 10 but less than 100 microwatts per square meter. CLASS X a solar X-ray burst with a peak flux at 1-8 angstroms, greater than or equal to 100 microwatts per square meter. MAJOR SOLAR FLARE a flare of optical importance (at least 2B - BRIGHT) with a centimetric outburst of 500 flux units or more; or an X-ray event of Class-X intensity of duration 3 hours or more regardless of optical flare importance. PROTON FLARE protons by satellite detectors (or polar cap absorption by riometer) have been observed in time associated with Ha flare. SATELLITE LEVEL PROTON EVENT a proton enhancement detected by Earth orbiting satellites with measured particle flux of at least 10 protons per square centimeter per second per steradian of at least 10 Million electronvolts. POLAR CAP ABSORPTION proton-induced absorption at least 2 dB as measured by a 30 MHz riometer located within the polar cap. STRATWARM reports of stratospheric warmings in the high latitude regions of winter hemisphere of the earth associated with gross distortions of the normal circulation associated with the winter season Inquiries regarding these messages should be address to NOAA, Space Environment Services Center R43, Boulder, CO 80303. These messages are also available by dialing (303) 499-8129 PROPAGATION FORECASTS The radio propagation forecasts broadcast on WWV were discontinued on September 30, 1976. Some of the information previously contained in these forecasts is now included in the Geophysical Alert announcements at 18 minutes after each hour. However, neither NBS nor the Space Environment Services Center which sponsors the Geophysical Alerts make radio propagation predictions, nor do they maintain a literature file on the subject. Users interested in further reading material on the effect of solar and geophysical activity on radio propagation should consult the latest edition of the AMATEUR RADIO HANDBOOK, published by the American Radio Relay League. MARINE STORM WARNINGS Weather information about major storms in the Atlantic and eastern North Pacific are broadcast in voice from WWV at 8, 9, and 10 minutes after each hour. Similar storm warning covering the eastern and central North Pacific are given from WWVH at 48, 49, and 50 minutes after each hour. An additional segment (at 11 minutes after the hour on WWV and at 51 minutes on WWVH) may be used when there are unusually widespread storm conditions. The brief messages are designed to tell mariners of storm threats in their areas. If there are no warnings in the designated areas, the broadcasts will so indicate. The ocean areas involved are those for which the U.S. has warning responsibility under international agreement. The regular times of issue by the National Weather Service are 0500, 1100, 1700, and 2300 UTC for WWV and 0000, 0600, 1200, and 1800 UTC for WWVH. These broadcasts are updated effective with the next scheduled announcement following the time of issue. Mariners might expect to receive a broadcast similar to the following: "North Atlantic weather West of 35 West at 1700 UTC. Hurricane Donna, intensifying, 24 North, 60 West, moving Northwest, 20 knots, winds 75 knots; storm 65 North, 35 West, moving east, 10 knots; winds 50 knots, seas 15 feet." Information regarding these announcements may be obtained from the Director, National Weather Service, Silver Spring, MD 20910. 1g. "Silent" Periods These are periods with no tone modulation. However, the carrier frequency, seconds pulses, time announcements, and 100-Hz BCD time code continue. END TRANSCRIPTION I have ended the transcription from the original literature here. The remaining material is on WWVB, the 60 kHz sister station to WWV and WWVH, and other totally unrelated topics. Here's a few more things you might like to know (TRIVIA): The telephone numbers listed in Figure 1 dial-in directly to the broadcasts of WWV and WWVH. If you don't have a radio, this is the only way to get these broadcasts The station identification and time-of-day announcement are pre- recorded -- not "live". The announcer for WWV is Don Elliott of Atlanta, Georgia. Mrs. Jane Barbe is the announcer for WWVH, and she is also from Atlanta. TOURS: Guided tours are available at all NBS radio station. However, arrangements for visiting the sites should be made in advance with the EIC. There aren't any 'regular' visiting hours. Tours of the NBS Boulder Labs, including visits to the atomic clock and the other dissemination services, are available. Information can be obtained from the Program Information Office, NBS, Boulder, CO 80303. Correspondence pertaining directly to station operations may be address to: Engineer-in-Charge NBS Radio Stations WWV and WWVB 2000 East County Road 58 Fort Collins, CO 80524 (303) 484-2372 Engineer-in-Charge NBS Radio Station WWVH PO Box 417 Kekaha, Kauai, HI 96752 (808) 335-4361 If you wish to receive the document I have copied this material from, so that you can read about the other frequency standard and about radio station WWVB at 60kHz, write to the station locations given in Figure 1 and ask for the document entitled "NBS TIME AND FREQUENCY DISSEMINATION SERVICES". vy 73 de KB9FRJ "Kyle"