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Radio Direction Finding, 10Kc/S to 550 Kc/S

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Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection 1957 Radio direction finding, 10kc/s to 550 kc/s. Weaver, Walter C. Monterey, California: Naval Postgraduate School, 1957. http://hdl.handle.net/10945/14543 RADIO OIREOTiQN FINDING 10 kc-s to 550kc-s Walter C. Weaver RADIO DIRECTION FINDING 10 kc/s to 550 kc/s 6 * * * * * Walter C. Weaver RADIO DIRECTION FINDING 10 kc/s to 55p kc/s by Walter C. Weaver Lieutenant, United States Navy Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN ENGINEERING ELECTRONICS United States Naval Postgraduate School Monterey, California 19 5 7 RADIO DIRECTION FINDING 10 kc/s to 550 kc/s by Walter C. Weaver This work is accepted aa fulfilling The thesis requirements for the degree of MASTER OF SCIENCE IN ENGINEERING ELECTRONICS fran the United States Naval Postgraduate School ABSTRACT This paper reviews the problems involved in the location of a non-cooperative transmitter in the 10 kc/s to 550 kc/s range. The infor- mation is presented in simplified form for easier understanding by non- technical personnel. Formulas and references are given for the engineer's use. The paper covers propagation characteristics, theoretical methods of radio location, and practical radio direction finder systems now in use or that may be used. An evaluation of the advantages and disadvan- tages of most of the practical systems is given. ii FORWARD The purpose of this paper is to present the problems involved in locating a non-cooperative transmitter that is transmitting in the fre- quency range from 10 kc/s to 550 kc/s. It is intended that the material be presented such that a non-technical person may grasp the ideas involved in radio direction finding, yet at the same time, to present sufficient theory and references that the engineer may continue into the problem. Radio direction finding is as old as radio itself. It has been used primarily for navigation and for the location of non-cooperative transmitters. Between World Wars I and II there was a great concentra- tion of effort on the use of frequencies above 1500 kc/s and as a conse- quence, most of the work on radio direction finding was done on the higher frequencies. The advent of World War II brought a renewed interest in the use of the very low and the low frequencies, especially in the field of navigation signals. It is because of this renewed interest in the lower frequencies that this paper is written. The writer wishes to express his appreciation for the assistance and encouragement given to him in this investigation by Professors John Downing and Donald Stentz of the Department of Electronics of the United States Naval Postgraduate School and to Messrs. Henry Blanchard and i a John Preidqkiet of the Radio Systems Laboratory of Stanford Research Institute at Menlo Park, California. iii SYMBOLS AND ABBREVIATIONS 9 = Angle of arrival in azimuth (in radians unless otherwise noted) e * Voltage induced in an antenna N 3 Number of turns in a loop A = Area E = Field strength in micro-volts/meter 1 » Wave length of signal w = radians he Effective height of an antenna f b Frequency o c s Velocity of propagation (usually approximated to 3 X 10 meters per second) L = Inductance in henries r s Radius a Radius of conductors or a bundle of conductors taken as a unit Rr Radiation resistance R = Resistance (ohmic) Z s Impedance u at 4jt x 10 1.257 x 10" henries/meter d s Distance (generally separation of two antennas) t ss Time or time difference phase difference ^\ = an incremental change (this is a prefix) 1 » Current E «= Voltage In « Natural log (base £ ) -23 k » 1.38 x 10 joules/degree Kelvin Boltzmann's constant) iv 6 u » 10" uv/m » micro-volts per meter £f « bandwidth En = noise voltage £ so frequency to which the circuit is tuned a s angle of arrival in elevation h' » apparent height d* = apparent distance ^ a approximately f , a peak frequency deviation if an infinite number of antennas were used f = rotational frequency of the antenna A a minimum number of antennas for a maximum n/2 radians phase shift between antennas TABLE OF CONTENTS Page ABSTRACT ii FORWARD iii SYMBOLS AND ABBREVIATIONS iv CHAPTER I. COMMUNICATION AND PROPAGATION V 1.1 Communication at the Lower Frequencies 1 1.2 Navigational Signals ' 2 1.3 Written Messages 2 1.4 Spoken Messages 4 1.5 Pictorial Messages 5 1.6 Miscellaneous Transmissions 5 1.7 Problems of Transmission 5 1.8 Receiver Noise 6 \ 1.9 Antenna Noise 7 1.10 Atmospheric Noise 7 1.11 Radiated Power and Signal Strength 8 1.12 Ground Wave Propagation 11 1.13 Sky Wave Propagation 13 1.14 Propagation by a Combination of Ground and Sky Waves 17 II. METHODS OF RADIO DIRECTION FINDING 2.1 Theoretical Methods of Radio Direction Finding 21 2.2 Methods for Obtaining a Line of Bearing 21 2.3 Methods for Obtaining a Line of Range 21 Vi Page 2.4 Highly Directional Antennas 22 2.5 Direction Finding by Phase and/or Amplitude Comparison from Two or More Beamed Antennas 22 2.6 Line of Bearings by Null Antenna Systems 24 2.7 Line of Bearing by the Time Difference Method 24 2.8 Doppler Effect 26 2.9 Line of Range by the Signal Strength Method 27 2.10 Line of Range by the Angle of Arrival of the Sky Wave 27 2.11 Line of Range by Measurement of the Time Difference between the Arrival of the Ground Wave and the Sky Wave or Two or more Sky Waves 28 2.12 Line of Range by Around- the -World Time Difference Measurements ' 28 2.13 Correlation 29 III. PRACTICAL RADIO DIRECTION FINDERS 3.1 Types of Direction Finders 30 3.2 Factors in Selecting a Direction Finder System 31 IV. ROTATING LOOP SYSTEMS 4.1 Loop Antenna Theory 32 4.2 Loop Errors 33 4.3 Sense 36 4.4 Untuned Loop Design Factors 38 4.5 Tuned Loop Design Factors 42 4.6 Summary of Loop Antenna Information 43 4.7 The Single Loop, Manually Operated Direction Finder 45 4.8 The Single Loop Visual Direction Finder 47 vil Page 4.9 The Single Loop Automatic Direction Finder 50 4.10 The Parallel Loop Direction Finder 56 V. FIXED LOOP DIRECTION FINDER SYSTEMS 5.1 Direction Finding Systems Using Fixed Loops 59 5.2 The Radio Goniometer 59 5.3 Crossed Loop Antenna Systems 61 VI. ADCOCK DIRECTION FINDER SYSTEMS 6.1 The Adcock Antenna 64 6.2 Sensitivity of the Adcock Antenna 64 6.3 Adcock Antenna Errors 65 6.4 Adcock Direction Finder Systems 70 VII. POST-RECEIVER DIRECTION FINDER SYSTEMS USING MULTIPLE RECEIVERS AND CROSSED LOOPS OR ADCOCK ANTENNAS 71 VIII. POST-RECEIVER DIRECTION FINDER SYSTEMS USING ONE RECEIVER AND CROSSED LOOPS OR ADCOCK ANTENNAS 76 IX. THE DOPPLER DIRECTION FINDER SYSTEM 84 X. TIME DIFFERENCE DIRECTION FINDING 90 XI. SELECTION OF A RADIO DIRECTION FINDER SYSTEM 11.1 Selecting a Direction Finder System Given the Requirements 96 11.2 Example of the Selection of a Small, Portable Direction Finder System 98 11.3 Example of the Selection of a Fixed Station Direction Finder System 100 BIBLIOGRAPHY 104 APPENDIX Low and Very Low Frequency Propagation Equations 106 viii LIST 0? ILLUSTRATIONS Figure Page 1.1 Median Values of Radio Noise Expected for a Short Vertical Antenna 9 1.2 Eastern U. S. Summer Noise 10 1.3 Surface Wave Field Intensity for a Radiated Field Intensity of 186,400 uv/ra at One Mile 12 1.4 Angle of Incidence vs. Distance for a Curved Earth 15 1.5 Signal Strength vs. Distance for Sky Wave Trans- mitted over a Sea Path for One KW of Radiated Power 16 /• 1.6 Time Difference Between the Ground Wave and the First Ionosphere-Reflected Wave Propagated Over a Spherical Earth 18 1.7 Combined Ground and Sky Wave Field Strength Pattern vs. Distance 19 2.1 Amplitude Matching of Two Antenna Beams 23 2.2 Basic Time Difference Method 25 4.1 A Loop Antenna 34 4.2 Sense 37 4.3 Voltage Output of a Loop Across a Given Load 39 4.4 Loop Antenna Equations 41 4.5 Tuned Loop Antenna Circuits 44 4.6 A Single Loop, Manually Operated Direction Finder 46 4.7 Single Loop Visual Direction Finder 49 4.8 An Automatic Loop Direction Finder (1) 53 4.9 An Automatic Loop Direction Finder (2) 55 4.10 The Parallel Loop Antenna 58 5.1 A Radio Goniometer 60 6.1 Adcock Antennas 67 6.2 Adcock Antenna Equations 68 6.3 A Vertical Antenna 69 lx Pigure Page 7.1 The "Watson-Watt" System 74 7.2 Two Receiver "Watson-Watt" Type Direction Finder 75 8.1 A Post Receiver Direction Finder Using One Receiver 80 8.2 A Post Receiver Direction Finder System (1) 81 8.3 A Post Receiver Direction Finder System (2) 82 8.4 Single Receiver, Post Receiver Time Delayed Separation System 83 9.1 Doppler Effect 88 9.2 Doppler Direction Finder System 89 10.1 Time Difference Direction Finders 93 10.2 Time Difference vs. Bearing 94 10.3 Time Difference Accuracy vs. Bearing Required for a One Degree Error in Bearing 95 11.1 Summary of Direction Finder System Characteristics 99 CHAPTER I COMMUNICATION AND PROPAGATION 1.1 Communication at the Lower Frequencies. 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