A 11 10 3 07512T o NBS SPECIAL PUBLICATION 559 J U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards Time and Frequency Users' Manual NATIONAL BUREAU OF STANDARDS The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and the Institute for Computer Sciences and Technology THE NATIONAL MEASUREMENT LABORATORY provides the national system of physical and chemical and materials measurement; coordinates the system with measurement systems of other nations and furnishes essential services leading to accurate and uniform physical and chemical measurement throughout the Nation's scientific community, industry, and commerce; conducts materials research leading to improved methods of measurement, standards, and data on the properties of materials needed by industry, commerce, educational institutions, and Government; provides advisory and research services to other Government agencies; develops, produces, and distributes Standard Reference Materials; and provides calibration services. The Laboratory consists of the following centers: Absolute Physical Quantities 2 — Radiation Research — Thermodynamics and Molecular Science — Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities; provides engineering measurement traceability services; develops test methods and proposes engineering standards and code changes; develops and proposes new engineering practices; and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers: Applied Mathematics — Electronics and Electrical Engineering 2 — Mechanical Engineering and Process Technology 2 — Building Technology — Fire Research — Consumer Product Technology — Field Methods. THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following centers: Programming Science and Technology — Computer Systems Engineering. 'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. : Some divisions within the center are located at Boulder, CO 80303. Banroai mravm v. — JAN 1 8 1980 r\crt ftcc -£Lt/ Time and Frequency Users' Manual r\0- 5^ Edited by: George Kamas Sandra L. Howe Time and Frequency Division National Measurement Laboratory National Bureau of Standards Boulder, Colorado 80303 U.S. DEPARTMENT OF COMMERCE Luther H. Hodges, Jr., Under Secretary Jordan J. Baruch, Assistant Secretary for Science and Technology NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director Issued November 1979 Library of Congress Catalog Card Number: 79-600169 National Bureau of Standards Special Publication 559 Nat. Bur. Stand. (U.S.), Spec. Pubi. 559, 256 pages (Nov. 1979) CODEN. XNBSAV (Supersedes NBS Technical Note 695, May 1977) U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1979 For sale by the Superintendent of Documents, U.S. Government Printing Office. Washington, D.C. 20402 Stock No. 003-003-02137-1 - Price $6. (Add 2u percent additional for other than U.S. mailing). CONTENTS PAGE CHAPTER 1. INTRODUCTION: WHAT THIS BOOK IS ABOUT 1.1 WHO NEEDS TIME & FREQUENCY? 1 1.2 WHAT ARE TIME AND FREQUENCY ? 4 1.3 WHAT IS A STANDARD ? . 5 1.3.1 CAN TIME REALLY BE A STANDARD? 6 1.3.2 THE NBS STANDARDS OF TIME AND FREQUENCY 6 1.4 HOW TIME AND FREQUENCY STANDARDS ARE DISTRIBUTED 7 1.5 THE NBS ROLE IN INSURING ACCURATE TIME AND FREQUENCY 7 • 1.6 WHEN DOES A MEASUREMENT BECOME A CALIBRATION ? . .8 1.7 TERMS USED . 8 1.7.1 MEGA, MILLI, PARTS PER... AND PERCENTS ...... 8 1.7.2 FREQUENCY 10 1.8 DISTRIBUTING TIME AND FREQUENCY SIGNALS VIA CABLES AND TELEPHONE LINES . .11 1.9 TIME CODES 13 CHAPTER 2. THE EVOLUTION OF TIMEKEEPING 2.1 TIME SCALES 17 2.1.1 SOLAR TIME 17 2.1.2 ATOMIC TIME 18 A. Coordinated Universal Time ......... 19 B. The New UTC System 19 2.1.3 TIME ZONES 20 2.2 USES OF TIME SCALES 21 2.2.1 SYSTEMS SYNCHRONIZATION 21 2.2.2 NAVIGATION AND ASTRONOMY 22 2.3 INTERNATIONAL COORDINATION OF TIME AND FREQUENCY ACTIVITIES 23 2.3.1 THE ROLE OF THE INTERNATIONAL TIME BUREAU (BIH) 23 2.3.2 THE ROLE OF THE NATIONAL BUREAU OF STANDARDS (NBS) 23 2.3.3 THE ROLE OF THE U.S. NAVAL OBSERVATORY (USNO) AND THE DOD PTTI PROGRAM . 24 CHAPTER 3. THE ALGEBRA AND CONVENTIONS FOR TIME AND FREQUENCY MEASUREMENTS 3.1 EXPRESSING FREQUENCY DIFFERENCE (IN HERTZ, kHz, MHz , ETC.) 28 3.2 RELATIVE (FRACTIONAL) FREQUENCY, F (DIMENSIONLESS) 28 3.3 RELATIVE (FRACTIONAL) FREQUENCY DIFFERENCE, S (DIMENSIONLESS) . .28 3.4 EXAMPLE OF ALGEBRA AND SIGN CONVENTIONS IN TIME AND FREQUENCY MEASUREMENTS . 29 3.4.1 Television Frequency Transfer Measurements (covered in Chapter 7) .29 3.4.2 Television Line-10 Time Transfer Measurements (covered in Chapter 8) . 29 iii PAGE 3.5 USING TIME TO GET FREQUENCY 30 3.6 A MATHEMATICAL DERIVATION 31 3.7 DEFINITIONS 32 CHAPTER 4. USING TIME AND FREQUENCY IN THE LABORATORY 4.1 ELECTRONIC COUNTERS . .33 4.1.1 SOURCES OF COUNTER ERROR 34 4.1.2 FREQUENCY MEASUREMENTS 34 A. Direct Measurement . .35 B. Prescaling 35 C. Heterodyne Converters .......... 35 D. Transfer Oscillators .......... 37 4.1.3 PERIOD MEASUREMENTS 39 4.1.4 TIME INTERVAL MEASUREMENTS 40 4.1.5 PHASE MEASUREMENTS 42 4.1.6 PULSE-WIDTH DETERMINATION MEASUREMENTS 43 4.1.7 COUNTER ACCURACY 43 A. Time Base Error ... .43 B. Gate Error . 44 C. Trigger Errors . , .45 4.1.8 PRINTOUT AND RECORDING 48 4.2 OSCILLOSCOPE METHODS 48 4.2.1 CALIBRATING THE OSCILLOSCOPE TIME BASE ....... 49 4.2.2 DIRECT MEASUREMENT OF FREQUENCY 50 4.2.3 FREQUENCY COMPARISONS 50 A. Lissajous Patterns 50 B. Sweep Frequency Calibration: An Alternative Method . .55 4.2.4 TIME INTERVAL MEASUREMENTS 56 4.3 WAVEMETERS 56 4.4 HETERODYNE FREQUENCY METERS 57 4.5 DIRECT-READING ANALOG FREQUENCY METERS 58 4.5.1 ELECTRONIC AUDIO FREQUENCY METER 58 4.5.2 RADIO FREQUENCY METER 59 4.6 FREQUENCY COMPARATORS 60 4.7 AUXILIARY EQUIPMENT 60 4.7.1 FREQUENCY SYNTHESIZERS 60 4.7.2 PHASE ERROR MULTIPLIERS 61 4.7.3 PHASE DETECTORS 62 4.7.4 FREQUENCY DIVIDERS 63 A. Analog or Regenerative Dividers ........ 63 B. Digital Dividers ........... 63 4.7.5 ADJUSTABLE RATE DIVIDERS 64 4.7.6 SIGNAL AVERAGERS 65 iv PAGE 4.8 PHASE LOCK TECHNIQUES 66 4.9 SUMMARY '.67 CHAPTER 5. THE USE OF HIGH-FREQUENCY RADIO BROADCASTS FOR TIME AND FREQUE NCY CALIBRATIONS 5.1 BROADCAST FORMATS 69 5.1.1 WWV/WWVH 69 5.1.2 CHU 70 5.1.3 ATA 71 5.1.4 IAM 72 5.1.5 IBF 72 5.1.6 JJY 72 5.1.7 OMA . .74 5.1.8 VNG 74 A. Time Signals 74 B. Time Code 74 C. Announcements ............ 74 D. DUT1 Code 75 E. Accuracy ............. 75 F. Frequency and Time Generating Equipment ...... 75 5.1.9 ZUO 75 A. Carrier Frequencies and Times of Transmission . .76 B. Standard Time Intervals and Time Signals ...... 76 C. Standard Audio Frequencies ......... 76 D. Accuracy 76 E. DUT1 Code 76 5.2 RECEIVER SELECTION 81 5.3 CHOICE OF ANTENNAS AND SIGNAL CHARACTERISTICS 82 5.4 USE OF HF BROADCASTS FOR TIME CALIBRATIONS 86 5.4.1 TIME-OF-DAY ANNOUNCEMENTS 86 5.4.2 USING THE SECONDS TICKS 86 A. Receiver Time Delay Measurements ....... 86 B. Time Delay Over the Radio Path 87 C. Using an Adjustable Clock to Trigger the Oscilloscope . .88 D. Delayed Triggering: An Alternate Method that Doesn't Change the Clock Output 90 E. Using Oscilloscope Photography for Greater Measurement Accuracy . 92 5.4.3 USING THE WWV/WWVH TIME CODE 92 A. Code Format . 93 B. Recovering the Code . .94 5.5 USE OF HF BROADCASTS FOR FREQUENCY CALIBRATIONS 96 5.5.1 BEAT FREQUENCY METHOD 97 5.5.2 OSCILLOSCOPE LISSAJOUS PATTERN METHOD 98 5.5.3 OSCILLOSCOPE PATTERN DRIFT METHOD 100 5.5.4 FREQUENCY CALIBRATIONS BY TIME COMPARISON OF CLOCKS 100 v PAGE 5.6 FINDING THE PROPAGATION PATH DELAY 101 5.6.1 GREAT CIRCLE DISTANCE CALCULATIONS 101 ' 5.6.2 PROPAGATION DELAYS . 102 5.7 THE NBS TELEPHONE TIME-OF-DAY SERVICE 105 5.8 SUMMARY. 105 CHAPTER 6. CALIBRATIONS USING LF AND VLF RADIO TRANSMISSIONS 6.1 ANTENNAS FOR USE AT VLF-LF 107 6.2 SIGNAL FORMATS 107 6.3 PROPAGATION CHARACTERISTICS AND OTHER PHASE CHANGES 108 6.4 FIELD STRENGTHS OF VLF-LF STATIONS Ill 6.5 INTERFERENCE .113 6.6 USING WWVB FOR FREQUENCY CALIBRATIONS 113 6.6.1 PHASE-SHIFT IDENTIFICATION 114 6.6.2 METHODS OF FREQUENCY COMPARISON 115 6.7 USING OTHER LF AND VLF STATIONS FOR TIME AND FREQUENCY CALIBRATIONS .