AI-1 APPENDIX I GLOSSARY ABSORPTION WAVEMETER—A device used for measuring frequency, consisting of a tuned circuit or cavity that is loosely coupled to the frequency being measured. Maximum energy is absorbed at the resonant frequency. BOLOMETER—An rf detector that converts rf power to heat, which causes a change in the resistance of the material used in the detector. This change in resistance varies in proportion with the amount of applied power and is used to measure the amount of applied power. CALORIMETER—A device that measures rf power by measuring the heat the rf power generates. CAVITY WAVEMETER—An instrument used to measure microwave frequencies. The resonant frequency of the cavity is determined by its inside dimensions. COAXIAL-LINE WAVEMETERS—A shorted section of a coaxial line used to measure rf frequencies. It is calibrated in either wavelength or frequency. CROSS MODULATION—An intermodulation condition that occurs when a carrier is modulated by an undesired signal. CURRENT PROBE—An inductive device used for measuring the current in a conductor. Probes are designed to be clamped around the insulated conductor. CURRENT TRACER—An inductively coupled device used for tracing current paths to determine the cause of low-impedance faults on a printed-circuit board. DECADE RESISTOR (DECADE RESISTANCE BOX)—It typically has two or more sections, each containing 10 precision resistors wired to selector switches. A piece of test equipment that provides a ready source of various resistances for engineering and measurement applications. DECIBEL (dB)—A standard unit for expressing relative power levels as the ratio of power out to power in. dBm—A unit used to express power levels above or below a l-milliwatt reference level at a designated load impedance (usually 600 ohms). DIFFERENTIAL VOLTMETER—A precision voltmeter that measures an unknown voltage by comparing it to a precision internal-reference voltage supply. ELECTROSTATIC-DISCHARGE SENSITIVE (ESDS) DEVICE—Electronic components that are susceptible to damage from static charges. FIBER OPTICS—Conductors that are usually constructed of plastic or glass fibers that readily pass light. Used primarily for transmission of high-speed data over relatively short distances.