AI-1
APPENDIX I
GLOSSARY
ABSORPTION WAVEMETER—An instrument used to measure audio frequencies.
AMMETER—A meter used to measure current.
BACK RESISTANCE—The larger resistance value observed when you are checking the forward
resistance of a semiconductor.
BAND PASS FILTER—A tuned circuit that passes only a specific frequency.
BAND REJECT FILTER—A tuned circuit that does not pass a specified band of frequencies.
BARRETTER—A type of bolometer characterized by an increase in resistance as the dissipated power
rises.
BEAT FREQUENCY—The difference between the oscillator frequency and the unknown audio
frequency.
BEL—The unit that expresses the logarithmic ratio between the input and output of any given
component, circuit, or system.
BOLOMETER—A loading device that undergoes changes in resistance as changes in dissipated power
occur.
CAVITY WAVEMETER—An instrument used to measure microwave frequencies.
CONTINUITY—An uninterrupted, complete path for current flow.
CORRECTIVE MAINTENANCE—Used to isolate equipment failures. Includes replacement of
defective parts to return equipment to proper performance.
DAMPING—The process of smoothing oscillations of the meter pointer.
D’ARSONVAL METER MOVEMENT—The permanent-magnet moving coil movement used in most
meters.
dBm—An abbreviation used to represent power levels above or below a 1-milliwatt reference.
DUMMY ANTENNA—See DUMMY LOAD.
DUMMY LOAD—A resistor used to replace the normal load, which is specifically designed to have low
reactance and possess the ability to dissipate required amounts of power.
ELECTRODYNOMETER METER MOVEMENT—A meter movement using fixed field coils and a
moving coil; usually used in wattmeters.
EXTERNALLY EXCITED METER—A term used to describe meters that get their power from the
circuit to which they are connected.
