Since January of 1993, specific tests have been mandated by the FCC to maintain minimum quality levels. This practical, easy-to-read handbook helps cable television technicians and engineers keep up with system growth and technology advances by explaining how cable operators should make the tests required to comply with the new FCC 76.605 regulations, and by providing a complete introduction to the optimum use of spectrum analyzers. KEY TOPICS: Updated to include the new FCC 76.605 regulations. Covers TV signal and CATV distribution; measurement parameters; test instrumentation; performance measurements with signal analysis; noise measurements with the spectrum analyzer; antennas for radiation measurements; and AC power supplies for field testing. MARKET: For all engineers and technicians in the Cable Television industry responsible for maintaining and conducting tests of systems. Previously announced in the 9/94 PTR Catalog.
2. Through the Analyzer's Looking Glass.
3. System and Signal Review.
4. Measuring Carrier and Sideband Amplitudes.
5. System and In-Band Frequency Response.
6. Measuring Carrier and Sideband Frequencies.
7. Conquering Carrier-To-Noise.
8. Coherent Disturbances — Beating CSO and CTB.
9. Cross Modulation Investigated.
10. Modulation Distortion at Power Frequencies, Hum.
11. Finding Signals that Leak and Signals that Intrude — Leakage, Co-Channel, and Ingress.
12. Audio and Video Measurements.
Your job as a cable television technician or engineer continues to change as your cable system evolves. The last ten years have seen a doubling in the number of subscribers and a ten-fold increase in the services offered. These changes demand increased technical performance from your cable system and an increase in the complexity and frequency of system testing. This book will help you keep up with test and technology growth by teaching you the basics of broadband RF cable compliance and maintenance measurements using a general-purpose spectrum analyzer.
Common industry test procedures, including those developed in Hewlett- Packard's Santa Rosa cable television research and design lab, have been used. The spectrum analyzer, with its proven utility to the cable industry, provides quality measurements while giving you a graphic vision of the measurement results. It is the only single instrument capable of full compliance testing. I have used Hewlett-Packard spectrum analyzers, but have kept product-specific controls and features to a minimum in order to widen the book's versatility and lengthen its useful life.
The chapters are organized by measurement complexity, progressing from carrier amplitude and frequency, to the more complicated noise- and distortion-related testing. Interference, leakage, audio, and video measurements round out the final chapters. Appendices provide background references, including a glossary of common cable TV and spectrum analyzer terms, and a tutorial on differential gain, differential phase, and chrominance-to-luminance delay inequality.
In selling services in today's marketplace, the quality of service and efficiency of testing maximizes your company's return-on-investment. Therefore, where possible, emphasis is placed on making tests that do not interfere with the delivery of services to your subscribers. Making tests efficiently and without disrupting product delivery will become more important as competing entertainment comes knocking at your customers' information door.
I will feel successful about the work put into this book if, after applying the book's concepts, you find that your cable maintenance and proof testing jobs make more sense, are more efficient, and are a bit more fun.
This book will teach you how to make cable television system compliance measurements with a spectrum analyzer. Its text, graphics, and examples provide a background in measurement technology, along with signal and test theory. Don't let the word theo ry intimidate you. The emphasis is on the practical principles of television signals, measurement concepts, and system carriers, not their detailed mathematical analysis.
what you will learn
You will learn to make the proof-of-performance measurements with a spectrum analyzer, whether in the relative comfort of the head end, or in the field where time, temperature, and weather make efficient and accurate measurements important.
The measurements covered are for NTSC-specified signals with compliance to the U.S. Federal Communications Commission (FCC) Rules and Regulations for cable television systems. Quotes from these regulations are in their respective chapters. Many of th e techniques and guidelines apply to systems with PAL television standard signals since the modulation is similar, although channel and carrier spacing is different from NTSC, and wider modulation bandwidths require different measurement settings on the spectrum analyzer.
The examples in this book show step-by-step measurement procedures for compliance tests, including the amplitude and frequency of carriers, the hunt for intermodulation and cross modulation distortion products, the diagnosis of hum disturbances, and practical and system flatness tests. Each example is supported with material to help you understand the objectives, not just the law, of the pertinent compliance test, and how to get the best accuracy from the spectrum analyzer based upon measurement procedure and the analyzer's own data sheet specifications.
Learning is effective when reinforced with hands-on experience. This text can be used as the basis for a working course. Its examples serve as laboratory experiments when guided by a skilled cable television measurement practitioner. The examples have been written without using the key stroke sequences of any one specific spectrum analyzer model, although specifications, and features of Hewlett-Packard spectrum analyzers are prominent.
Look for Tips and Cautions
Tips and cautions are highlighted to help summarize the measurement. A tip puts the main point of the message in a few, large typeface words to help you stay on track. Cautions provide guidance to help avert common measurement or interpretations mist akes. They look like this:
Tips provide a summary of the local text.
Provides a warning about common measurement errors.
This course is intended for cable television technicians and engineers who have some experience with system and head end measurements. The information that appears to be reviews can be skipped, but will be valuable to those who have less measurement experience.
Knowledge of the spectrum analyzer and how it works is not a necessary prerequisite to learn from this book. The cable television test procedures will teach you all you need to know about spectrum analyzer operation, measurement circuits, specificati ons, and features. An appendix is provided to those of you who must see the innards of a spectrum analyzer. References to the analyzer's block diagram and components shown in this appendix will be cited from time to time in the text.
What You Can Do After Studying This Book
After studying and working through the examples of this book, you will be able to make a number of proof-of-performance measurements faster and with confidence in the accuracy of your measurement. Here is a sample of the tests covered: visual carrie r frequency and amplitude, aural signal frequency and amplitude, FM deviation, system noise level, carrier-to-noise ratio, depth of modulation, cross modulation, CTB/CSO, hum, in-channel frequency response, and system frequency response.
What You Need to Know About a Spectrum Analyzer
After saying that you don't need to know much about a spectrum analyzer, here is a primer for those of you who have never laid hands on one. The rest of you can skip to the next section!
The spectrum analyzer is just an ever-tuning radio receiver with a screen for viewing signals.
The spectrum analyzer is simply a receiver, like an ever-tuning radio, which displays signal amplitude over frequency. Think of it as a television receiver when the viewer has a finger pressing on the channel Up button of the remote control. The spec trum analyzer, unlike the television receiver, doesn't skip from frequency to frequency; it tunes continuously across the selected frequency span, and then starts over. It does not display a result of the signal at its input, such as a TV picture, bu t the signal's amplitude and frequency components. It displays any signal in its input range, as illustrated in Figure 1. The amplitudes and frequencies of the harmonics of the left-most signal are displayed.
Figure . A spectrum analyzer look at its calibration signal, at 300 MHz, and all its harmonics.
What a Spectrum Analyzer Does
The spectrum analyzer is calibrated specifically for the accurate display of continuous wave (CW) signals, even though there are few such signals in the world of communications and television. CW signals do not contain information by themselves, but can carry a great deal of information in their modulation. This modulation can be broken down into still further sidebands that appear as CW signals. And the analyzer can display these!
This is an oversimplification of the use of a spectrum analyzer; however, this basic understanding of the spectrum analyzer underlies all the procedures within this book.
Modulation of a CW signal can be viewed easily with the spectrum analyzer as sidebands.
How do you control what the analyzer does? Simple. The spectrum analyzer has inputs and outputs, a cathode ray tube (CRT) display, and keys to access its functions. The functions are grouped for convenience, the primary ones controlling the CRT displ ay of frequency and amplitude ranges. The preset key sets the analyzer to a known state. It is a safe and convenient reset button when you get confused about a measurement, when the analyzer decides to misbehave, or when you need a known starting poi nt. Most spectrum analyzers will preset when powered on. Figure 2 shows a representative spectrum analyzer front panel.
The modern spectrum analyzer, as with most contemporary test equipment, has an internal computer or microprocessor which allows the instrument to do much more at the touch of a single control. As an operator, you control the analyzer hardware and circuits through its computer by issuing commands to its microprocessor by pressing or turning front panel controls. Figure 2illustrates three types of controls called hardkeys, softkeys, and data entry controls. Hardkeys, often with a dedicated name on or near the key, enable the same function every time they are pressed. Softkeys, usually located adjacent to the CRT, may change definition depending upon the hardkey pressed. Softkey labels are shown on the CRT. Data controls are the number pad, un it keys, knob, and up and down keys. They are used to enter and change numeric settings by typing a number, or by stepping up or down through a predefined sequence.
Figure 3 shows a typical spectrum analyzer CRT display. The trace is annotated with up-to-the-minute analyzer amplitude and frequency states, control settings, and measurement messages. Amplitude level is given for the reference level, the top gratic ule, and a scale such as decibel (dB) per division. Frequency is shown as a center frequency and a total span or as start and stop frequencies. Note that frequency is given as full span rather than as a per division number as in older spectrum analyzers and most current oscilloscopes.
Figure . A typical spectrum analyzer front panel.
Figure . The display communicates all readout information. Other outputs include rear panel RF connectors, the loudspeaker, printer and plotter ports, and a computer port.
Promote your Skill, Understanding, and Interest
The aim of this book is to make you more knowledgeable in your job as an operator and technical professional in the maintenance of your cable television system. The background and skills taught will help you prevent subscriber dissatisfaction, satisfy the letter and intent of the compliance regulations, and provide you with more insight into trouble- shooting performance problems. It is hoped that the material here will assist in your professional growth. This growth will be necessary to meet f uture measurement challenges as cable systems add more services, move toward digital signal processing, and expand to a wide two-way data highway. Along the way, perhaps, the tools and understanding this book can provide will reduce the amount of str ess in your job, helping you to have more time and energy for a bit of technical exploration...in other words, some fun!
Code of Federal Regulations, Title 47, Telecommunications, Part 76, Cable Television Service. Federal Commission Rules and Regulations, 1990.
Peterson, Blake. Spectrum Analysis Basics. Hewlett-Packard Company, Application Note AN 150, Literature No. 5952-0292, Santa Rosa, CA, 1989.