Practical Radio Frequency Test and Measurement: A Technician's Handbook

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Practical Radio Frequency Test and Measurement will teach readers the basics of performing the tests and measurements used in radio-frequency systems installation, proof of performance, maintenance, and troubleshooting. Practical Radio Frequency Test and Measurement teaches readers the basics of performing the tests and measurements used in radio-frequency systems installation, proof of performance, maintenance, and troubleshooting. Anyone interested in gaining more practical proficiency with RF, whether engineer, technician, amateur radio buff, or hobbyist, needs a copy of this book. Joseph J. Carr, himself an accomplished practitioner in this field, examines the instruments used in the various types of measurement before moving on to specific measurement methods. Carr includes information on basic theories of RF measurement, as well as test equipment, test set-ups, test and measurement procedures, and interpretation of results. Provides immediate applications for anyone who works in or is interested in RF technology Suitable for beginners, intermediate-level users, and advanced users Written by a prolific expert in the RF field
Copyrighted Materials Copyright@2002ElsevierRetrievedfromwww.knovel.com PREFACE This book is about making measurements on radio frequency devices and in radio frequency systems. RF is different from low frequencies for a number of reasons The chief reason is that component sizes approximate wavelengths in many cases so they become very important. Also, in certain cases stray inductance and capac tance have a much more profound effect on RF circuits than they do on lower fre quency circuits. In this book you will find information about a number of topics, including the basic theories of rF and any other form of measurement, as well as some useful rF components for test and measurement. The Smith Chart is covered (it would be a contradiction to leave it out). Additional topics include: signal sources and signal generators; spectrum and network analyzers; RF power mea surement; measurement of time, frequency, and period; radio receiver measure ments;radio transmitter measurements; RF amplifier (including high-power amplifier)measurements; antenna gain and pattern measurement; antenna and transmission line measurements; L-C-Rmeasurements at RF frequencies; and man ual Time Domain Reflectometry(TDr)measurements My approach taken is to examine the instruments used in the various types of measurement and then to look at practical measurement methods. The latter is not always easily understood without knowledge of the former Joseph J. Carr, MSEE Falls Church, virginia Copyrighted Materials Copyright@2002ElsevierRetrievedfromwww.knovel.com C○ NTENTS Preface 1 INTRODUCTION TO RADIO FREQUENCY ELECTRONICS AND MEASUREMENT THEORY 2 SMALL COMPONENTS USED IN RADIO FREQUENCY TEST AND MEASUREMENT 3 SMITH CHARTING THE RADIO FREQUENCY CIRCUIT 49 4 SIGNAL SOURCES AND SIGNAL GENERATORS 5 SPECTRUM AND NETWORK ANALYZERS 102 6 RADIO FREQUENCY POWER MEASUREMENTS 121 7 MEASURING FREQUENCY AND PERIOD 151 8 RADIO RECEIVERS AND THEIR MEASUREMENTS 167 9 RADIO TRANSMITTER MEASUREMENTS 21 10 AMPLIFIER MEASUREMENTS 264 I1 ANTENNA GAIN AND PATTERN MEASUREMENTS 287 viIi Contents 12 ANTENNA AND TRANSMISSION LINE MEASUREMENTS 293 13 MEASURING INDUCTORS AND CAPACITORS AT RF FREQUENCIES 322 14 TIME-DOMAIN REFLECTOMETRY 335 Bibliography 341 343 Copyrighted Materials Copyright@2002ElsevierRetrievedfromwww.knovel.com CHAPTER ONE Introduction to Radio Frequency Electronics and Measurement Theory The physicist Lord Kelvin once remarked that one doesn'treally understand a thing until one can measure it and assign numbers to it. Measurement is the assignment of numbers to represent the attributes or properties of something according to a standard rule that gives the numbers an ordered meaning. Measurements are also used for qualitative data but the results tend to be bivalent (two-valued) such as true or false yes or no, 1 oro, and so on This book discusses the various methods used for measuring radio frequency circuits and systems. But first i will discuss the basic theories of all forms of electronic measurements, which will help the rest of the material make more sense MEASUREMENTS Measurements are made to fulfill any or all of several different goals Obtain information about a physical phenomenon assign a value to some fundamental constant Record trends in, or control, some process; and Correlate behavior of a phenomenon with other parameters in order to ob tain insight into their relationships Measurement is an act designed to derive quantitative information about some phenomenon "by comparison to a reference"(Herceg, 1972). The physical quantity being measured is called the measurand or factor. Measurement Data Classes The data that results from measurements can be divided into two major classes and those classes are each divided into two subclasses. The major divisions include qualitative data and quantitative data 2 INTRODUCTION TO RADIO FREQUENCY ELECTRONICS AND MEASUREMENT THEORY Qualitative Data This type of data is nonnumerical or categorical in nature. It includes things like the presence or absence of some factor, good or bad, defective or not defective, ger der, race, and so forth Qualitative data doesn t inherently result in numbers, so it is sometimes held in less esteem than quantitative data. This attitude is mistaken, unless there is some inherent need for numbers in a particular case. Qualitative data can be further broken into two subgroups: nominal data and ordinal data Nominal data is qualitative data that has no inherent ordering or rank. Exam ples include lists of names, labels, groupings, and so forth. Ordinal data allows ranking, but differences between data points are either nonexistent or meaningless Qualitative data can sometimes be given a numerical flavor by correct col- lection techniques. For example, because much of this data is bivalent in nature one can assign the digits 0 and 1( e.g 1 foryes"and 0 for"no"). Another popu lar method is to assign some arbitrary but consistent scale indicating depth of feel ing, preferences, and so forth. For example, a scale is often used to assign numerals to questions that are largely qualitative value judgments Quantitative Data Quantitative data is that which naturally results in some number to represent the factor. Examples include amount of money, length, temperature, number of defects per unit, voltage, pressure, weight, frequency, period, phase, power, and so on Quantitative data can be further divided into two subclasses: interval data and ratio data. Interval data allows for a meaningful comparison of differences, but not the relative values of two or more factors Such measurements are made rela- tive to an arbitrarily selected standard zero point. For example, in the West we as sign calendar dates according to the supposed birth date of Christ. In other cultures, the zero point is some other fixed historical event Another example of an interval measure is temperature, as measured on the Celsius(centigrade)and Fahrenheit temperature scales (oC and"F, respectively) The Celsius scale sets the zero degree point at the freezing point of water. Another arbitrary(but convenient)reference point on the Celsius scale is the 100C point the boiling point of water Why are these points used to define the Celsius scale? Aren't they somewhat arbitrary? The reason these points are used is that they are easy to replicate when- ever anyone wants to calibrate a celsius thermometer. In other words one doesn 't need a high-quality metrology laboratory to do a reasonably good job of calibrat- ing a common thermometer. e Celsius scale is also sometimes called"centigrade"because there are 100 (centi)equal divisions between the arbitrarily setoC and 100C points. The zero point on the Fahrenheit scale is equally arbitrary, but its selection seems a bit irra tional (water freezes at 32 F Why are the Cand 100C points on the Celsius scale arbitrary? Because there is no particular compelling reason to select these points, except for calibration con- venience. After all, there are temperatures colder than 0C and hotter than 100C The selection of zero points on the temperature scale illustrates the properties of interval data: we can make meaningful statements about differences of temper- Measurements ature but differences cannot be scaled up; that is 40oC is not twice as much tem- perature as 20C(see Figure 1.1). Ratio data are based on some fixed or natural zero point: for example, weights, pressures, and temperatures such as the Kelvin scale. The Kelvin temperature scale uses degrees of the same size as in the Celsius scale(a change of 1oC is the same as a change of 1K), but the zero reference point is what physicists call absolute zero"that is the temperature at which all molecular motion ceases (oKis about-273.16C). Thus, 0 Represents a natural zero point a consequence of having a natural zero reference point is that ratios as well as differences are meaningful. Raising a temperature from 100 K to 200 Kis an in crease of twice the temperature Measurement standards Metrology, the science of measurement, requires arule"to which things are com- pared; that rule is called a standard. Not all standards are equal, so there is a hier- archy of standards(Figure 1.2): international reference standards, primary standards, transfer standards, working standards, and shop-level standards International Reference Standards These standards are those agreed upon by an international standards organization For years, the reference standard for the meter was a platinum bar, 1.0000 meters long, stored in a vault in Paris, France, maintained by the international Standards In- stitute. Various authorities around the world keep other international standards 40°C 20C Ure Absolute When examined against absolut zero,40° is nof twice20° 273° despite what the relative numbers might indicate INTRODUCTION TO RADIO FREQUENCY ELECTRONICS AND MEASUREMENT THEORY INTERNATIONAL REFERENCE STANDARDS NATIONAL PRIMAR STANDARDS TRANSFER STANDARDS SHOP-LEVEL DEVICE UNDER TEST STANDARDS VORKING STANDARDS 辑8◎ 8◎ Figure 1.2 Hierarchy of standards for testing instruments Primary Standards These are the principal standards maintained at a national level in the various countries. In the united States these standards are maintained by the national in stitutes of Standards and Technology(Nist), formerly, named the National Bureau of Standards(NBs). Some primary standards are periodically compared with an in- ternational reference standard maintained by a group such as the International Standards institute Transfer tandards These standards are second level, and are periodically compared with the primary standard. They are used to calibrate lower-order standards used in the country so that wear and tear on the primary standard is reduced Working Standards The working standard is compared with the transfer standard in a nationally cer tified laboratory or at nist. Such standards are said to be" Nist traceable. Shop Level and Secondary Standards These standards are used locally(e.g, in the lab)to calibrate instruments and gauges. Gauges/Instruments The lowest order of standards these are the devices actually used to make mea surements and collect data on the objects being measured. Gauges and Instruments are compared with either working standards or secondary standards Measurements Categories of Measurement There are three general categories of measurement: direct, indirect, and null. Elec tronic instruments are available based on all three categories Direct measurements are made by holding the measurand up to some cali- brated standard and comparing the two. a good example is the ruler used to cut a piece of coaxial cable to the correct length. You know that the cable must be cut to a length of 56 cm, so you hold a meter stick(the standard or reference) up to the uncut piece of cable( Figure 1.3). Set the"0 cm"point at one end, and make a mark on the cable adjacent to the" mark on the meter stick, and then make your cut t the appropriate point. Indirect measurements are made by measuring something other than the ac tual measurand. Although frequently considered"second best"from the perspec- tive of measurement accuracy, indirect methods are often used when direct measurements are either difficult or dangerous. For example one might measure the temperature of a point on the wall of a furnace that is melting metal, knowing that itis related to theinterior temperature by a certain factor. There was once a mini computer manufacturer who used an indirect temperature measurement to ease the job of the service technicians. The manufacturer drilled a small hole at the top of the rack-mounted cabinet where the temperature would be <39C when the tempera ture on the electronic circuit boards deep inside the cabinet was within specification Although the technicians were interested in the temperature at the board level, they actually make a measurement that correlates to the desired measurement. The system manufacturer specified this method for two reasons 1. The measurement point was easily available(while the boards were not )and thus did not require any disassembl 2. The service technician could use an ordinary medical fever thermometer (30C to 42C) from a corner drug store as the measurement instrument An example of indirect measurement in radio frequency(RF)is measuring the heat generated when RF power is dissipated in a resistive load, and then calculating the RF power level from the temperature change information Null measurements are made by comparing a known (calibrated value to an Inknown measurand and then adjusting either one or the other until the differ- ence between them is zero. an electrical potentiometer is such an instrument; it is an 56 cm 0 cm Figure 1. 3 Measuring cable with a ruler.

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