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narionsi t5urea« or standarefl FEB 2 0 1973 (Pdico the Development of Loran-C 7^^"^ Navigation and Timing Gifford Hefley Institute for Basic Standards U > i National Bureau of Standards Boulder, Colorado 80302 U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretary NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Aciing D/rec/or, Issued October 1972 Library of Congress Catalog Card Number: 72-600267 National Bureau of Standards Monograph 129 Nat. Bur. Stand. (U.S.), Monogr. 129, 157 pages (Oct. 1972) CODEN: NBSMA6 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.44:129). Price $4.50. Stock Number 0303-01060 TABLE OF CONTENTS Page iv LIST OF FIGURES vii LIST OF TABLES viii ABSTRACT ix FOREWORD, L. E. Gatterer X FOREWORD, Robert H. Doherty xi PREFACE 1 1. INTRODUCTION 5 EARLY DEVELOPMENT OF LORAN AND GEE 2. 8 3. LOW- FREQUENCY LORAN, CYCLAN AND WHYN 25 4. CYTAC DEVELOPMENT AND PRELIMINARY TESTS 35 5. CYTAC FIELD TESTS 35 5.1. General Description of Test Program 39 5.2. Summary of Field Measurements 39 5.2.1. Baseline Extension Measurements 42 5.2.2. Random Errors 47 5.2.3. Systematic Errors 47 5.2.4. Flight Tests (Random and Systematic Errors) 59 5.3. Rate of Change of Systematic Errors 63 5.4. Localized Phase Errors 64 5.5. Instrumentation Errors 66 5.6. Temporal Variations 68 5.7. Skywaves 6. LORAN-C — AN OPERATIONAL SYSTEM 72 7. LORAN-C TIMING 9 3 7.1. Background 9 3 7.2. Time and Distance 9 3 7.3. Evolution of Timing Requirements 95 98 7.4. The Loran-C Clock 98 7.5. Timing Receiver 7.6. Divider Chain and Clock Readout 99 7.7. Identification of Larger Units of Time 100 100 7.8. UHF Time-Distribution System 7.9. AMR Timing Tests 7.10. Monitoring and Steering 7.11. Timing with Specific Repetition Rates 1 n Q 8. LORAN-C SKYWAVES 9. CALIBRATION OF A LORAN-C SYSTEM 12 4 10. ACKNOWLEDGEMENTS 136 11. GLOSSARY OF SPECIALIZED TERMS AND SYMBOLS 137 12. REFERENCES 139 13. BIBLIOGRAPHY 141 111 LIST OF FIGURES Page 3.1. LF loran monitoring sites and test-flight routes (Signal Corps). 9 3.2. Loran triad geometry. 10 3.3. Average transmission delay corrections for LF Loran (Signal Corps). 12 3.4. Camp Ripley data (Signal Corps). 13 3.5. Wright Field data (Signal Corps). 13 3.6. Distribution of daytime errors, Wright Field (Signal Corps). 14 3.7. Distribution of nighttime errors, Wright Field (Signal Corps). 14 3.8. Loran grid for square configuration of transmitters (Signal Corps), 14 3.9. Gyclan mobile receiver. 21 3.10. Cyclan baseline extension data. 22 4.1. Sperry technique for marking a point on the Loran-C pulse. 26 4.2. NBS pulse scheme. 27 4.3. Scope photograph of NBS pulse. 2 8 4.4. NBS pulse monitoring locations. 29 4.5. Pulse envelope tracings. 30 4.6. Cytac envelope deviations ordinate value not exceeded 90 percent of time. 31 4.7. Cytac ground- and skywave measurements. 32 4.8. Geometric representation of skywave paths. 32 5.1. Cytac transmitters and grid. 39 5.2. Cytac monitoring sites. 40 5.3. Forestport (S2) baseline extension. 40 5.4. Forestport measurements. Smooth curves are for a = 0.001. 41 5.5. Forestport measurements. 42 5.6. Readings at Williams Bay, Wisconsin. 44 5.7. Reading at Smith Center, Kansas. 44 5.8. Readings at Drakesboro, Kentucky. 44 5.9. Readings at Dayton, Tennessee. 44 5.10. Readings at Twin City, Georgia. 44 5.11. Circular and elliptical distribution of errors, 50% of fixes. Williams Bay, Wiscons;in. 45 5.12. Circular and elliptical distribution of errors, 50% of fixes. Smith Center, Kansas. 45 5.13. Circular and elliptical distribution of errors, 50% of fixes. Drakesboro, Kentucky. 45 5.14. Circular and elliptical distribution of errors, 50% of fixes. Dayton, Tennessee. 45 5.15. Circular and elliptical distribution of errors, 50% of fixes. Twin City, Georgia. 46 5.16. Contours of constant time-difference corrections (S^) . 48 5.17. Contours of constant time-difference corrections (32)- 48 5.18. S^ readings, Dayton, Tennessee. 50 5.19. S2 readings, Dayton, Tennessee. 50 5.20. Tracks of aircraft flying over GMR, Dayton, Tennessee. 50 5.21. Simulated bombing runs. The unadjusted prediction shows the error that would have been made without using the correction contours. 58 iv LIST OF FIGURES (Cont'd) Page 5.22. Simulated bombing runs. The unadjusted prediction shows the error that would have been made without using the correction contours. 58 5.23. A plot of the miss distances vs. distance from the nearest GMR site. 59 5.24. Area where systematic corrections were studied. 60 5.25. Airborne and ground measurements of systematic corrections. 61 5.26. Airborne measurements of systematic errors. 61 5.27. Measured systematic errors. 62 5.28. Airborne measurements of systematic corrections. Dashed curves - flying east. Solid curves - flying west. (See fig. 5.26 for locations.) 6 2 5.29. Additional systematic correction measurements near Bryson City, North Carolina. 62 5.30. Measurements along U.S. Highway 11, near Riceville, Tennessee. 6 3 5.31. Time-difference errors from figure 5.30. 64 5.32. Time-difference readings with and without phase coding - Dayton, Tennessee. 65 5.33. Simultaneous S^ time-difference readings. 65 5.34. Running average of Clark ton. North Caroline S2 time difference, November 30 to Decen±>er 1, 1954. 67 5.35. and S2 average cycle readings at Clarksdale, Mississippi (Rena). 67 5.36. Sj^ and S2 daily average cycle readings at Clarkton, North Carolina (Rodgers). 6 8 5.37. First-hop skywave measurements, Carolina Beach to Boulder. 70 6.1. Martha's Vineyard station during construction. 73 6.2. Jupiter station after completion. 73 6.3. Jupiter transmitter (AN/FPN 15). 74 6.4. Bermuda fixes - September, 1957 to August, 1958, 8-hour averages. (Jansky & Bailey). 78 6.5. Bermuda fixes - September 4-6, 1957, 15-min averages (Jansky & Bailey) . 78 6.6. Airborne fixes. Little Sale Cay (Jansky & Bailey). 80 6.7. Airborne fixes, Bassett Cove (Jansky & Bailey). 80 6.8. Airborne fixes. Walker Cay (Jansky & Bailey). 80 6.9. Loran-C Chains. 83 6.10. Jan Mayen Island station. 83 7.1. Time-scale distribution by Loran-C transmitter. 94 7.2. Relative gain or loss of independent clocks. 9 7 7.3. Loran-C clock. 9 8 7.4. Pulse group tc time relationship. 100 7.5. Synchronization of two clocks to check propagation. 102 8.1. Regions where the majority of skywave measurements have been made. 116 8.2. Phase and amplitude of the Loran-C skywave recorded on a north-south path. 117 First-hop skywave from Carolina Beach, North Carolina to Boulder, Colorado. 117 V LIST OF FIGURES (Cont'd) Page 8.4. First-hop skywave from Carolina Beach, North Carolina to Boulder, Colorado. 118 8.5. First-hop skywave from Carolina Beach, North Carolina to Boulder, Colorado 118 8.6. First-hop skywave from Carolina Beach, North Carolina to Boulder, Colorado. 119 8.7. Solar event of September 28, 1961. 119 8.8. Wake Island, Nov. 1, 1963. 121 8.9. Wake Island, Nov. 8, 1963. 121 8.10. Wake Island, May 1, 1964. 8.11. Wake Island, May 2, 1964. 8.12. Wake Island, July 10 , 1964. 3^22 9.1. Secondary-phase corrections as a function of distance in parametric conductivity. j2 8 9.2. Secondary-phase corrections as a function of distance parametric in conductivity. 128 9.3. Rate of change of secondary correction at a great distance as a function of conductivity. 129 9.4. Example plot of readings taken at 30 and 100 km from near transmitter. 130 9.5. Typical master station location. 133 vi LIST OF TABLES Page 3.1. Standard Deviation of Measurement Errors and Time Differences - ys . 15 5.1. Cytac Test-Site Locations. 37 5.2. Periods of Observation. 43 5.3. Major and Minor Semi- Axis of 50 Percent Error Ellipses. 46 5.4. Cytac Errors Ba&ed pn Conductivity Corrections 48 5.5. C-47 Flights at Dayton, Tennessee (Evensville). 52 5.6. C-47 Flights at Twin City, Georgia (Canaday) . 53 5.7. C-47 Flights at Savannah, Georgia (Chester). 54 5.8. C-47 Flights at Titusville, Florida (Wilson). 55 5.9. C-47 Flights at Ft. Myers, Florida (Punta Rassa) . 56 5.10. Miss Distances Associated with Bombing Runs. 57 5.11. Site Locations for Calibrating Flights. 60 5.12. Daytime Skywave Measurements. 69 6.1. Time and Data Percentages - Feb. 3 to Aug. 2 8, 195 8. 75 6.2. Transmitter Interruptions for Period June 2 to July 3, 1958. 76 6.3. Measured vs. Predicted TDs . 81 6.4. Present Operational Loran-C Chains. 82 7.1. Results of the AMR Tests. 104-105 7.2. Lor an Repetition Rate Periods. 106 7.3. Intervals in seconds at which pulse groups coincide with whole seconds. 107 8.1. Measurements Made on Caribbean Trip. llp S.'l. Time-Difference Measurements (Jansky & Bailey Measurements). 112 8.3. Summary of Measured Skywave Corrections (Jansky & Bailey Measurements) . 113 vii ABSTRACT The Loran-C timing and navigation concept and its implementation in the form of the Loran-C system has taken on considerable importance in a variety of military and civilian applications such as microsecond clock synchronization, precision tactical or civil navigation, etc. Future applications like tying together continental surveys , aircraft collision avoidance, etc., have yet to be explored in detail.
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