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CHAPTER 4
QUALITATIVE MEASUREMENTS
LEARNING OBJECTIVES
Upon completion of this chapter, you will be able to do the following:
1. Identify the various methods of measuring standing-wave ratios.
2. Identify the various methods of determining electrical losses caused by deterioration of
transmission lines.
3. Identify the methods of measuring intermodulation distortion.
INTRODUCTION TO QUALITATIVE MEASUREMENTS
As a technician, you are responsible for repairing and maintaining complex electronic systems. The
basic ability to repair a specific piece of equipment is only the first step in becoming a qualified
technician. Your ultimate goal should be to become proficient at systems fault isolation — in other words,
to know the entire system like the back of your hand. To reach this goal you will need to be familiar with
all parts of the system and know how they are interconnected and interact with each other. There are
numerous shortcuts or tricks of the trade that can only be learned through experience on any system, but
the most practical thing for you to remember is to approach all problems in a logical manner.
Various combinations of electronic equipment are interconnected to form a system capable of
performing specific functions. You must be able to apply general test methods and practices to
installation, tuning, maintenance, and repair of the system. This requires you to have a thorough
knowledge of many types of electronic equipment. When radar, communication, and digital computers
are interconnected, they require different maintenance procedures than when they are operated separately.
Revised test procedures may be necessary. Detrimental interactions between equipment or facilities must
be corrected and effective preventive maintenance procedures must be planned for all equipment within
the system. System quality figures, such as sensitivity and coverage, must be determined and measured
during equipment preventive maintenance checks to assure efficient operation. System monitoring at
specific test points is often used to help localize a problem.
System testing and monitoring are frequently accomplished by using an external piece of electronic
equipment, which is designed specifically for testing a particular system. Some computers and computer
systems build in their own monitoring and testing devices and will inform the operator when and where
failure has occurred. You must realize that any equipment designed to test, monitor, or repair another
system is itself subject to malfunction and will require periodic checks and preventive maintenance. This
chapter will cover some of the basic test methods and practices associated with system-level
troubleshooting.
