FACSIMILE - The method for transmitting and receiving still images. These
images can be maps, photographs, and handwritten or printed text .
FACTOR - Any of the elements, quantities, or symbols that, when multiplied
together, form a product .
FADING - Variations in signal strength by atmospheric conditions [101 .
FARAD - The basic unit of capacitance. A capacitor has a capacitance of 1
farad when a voltage potential of 1 volt across it produces a charge of 1 coulomb .
FARADAY ROTATION - The rotation of the plane of polarization of
electromagnetic energy when it passes a substance influenced by a magnetic field that has
a component in the direction of propagation .
FAST-TIME-CONSTANT CIRCUIT - Differentiator circuit in the first video
amplifier that allows only the leading edges of target returns, no matter how small or
large, to be used .
FEEDBACK - The return of a portion of the output of a circuit to its input
.
FEEDER - A transmission line that carries energy to the antenna .
FEEDHORN - A horn radiator used to feed a reflector .
FEP - A synthetic type of insulation (fluorinated ethylene propylene) .
FERRITE - A powdered and compressed ferric oxide material that has both
magnetic properties and light resistance to current flow .
FERRITE SWITCH - A ferrite device that blocks the flow of energy through a
waveguide by rotating the electric field 90 degrees. The rotated energy is then reflected
or absorbed .
FERROMAGNETIC MATERIAL - A highly magnetic material, such as iron, cobalt,
nickel, or their alloys .
FERRULES - The cylindrical metallic ends of a cartridge fuse .
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.
FIBROUS BRAID - An outer covering used to protect a conductor's insulating
material. Commonly made from cotton, linen, silk, rayon, or fiberglass .
FIDELITY - (1) The faithful reproduction of a signal. (2) The accuracy
with which a system reproduces a signal at its output that faithfully maintains the
essential characteristics of the input signal .
FIELD - The electromagnet which furnishes the magnetic field that
interacts with the armature in motors and generators .
FIELD, DATA - An item of information in a data record. One or more related
characters that are treated as a unit of information.
FIELD-EFFECT TRANSISTOR (FET) - A transistor consisting of a source, a
gate, and a drain. Current flow is controlled by the transverse electric field under the
gate .
FIELD EXCITATION - The creation of a steady magnetic field within the
field windings by the application of a dc voltage either from the generator itself or from
an external source .
FIELD OF FORCE - A term used to describe the total force exerted by an
action-at-a-distance phenomenon such as gravity upon matter, electric charges acting upon
electric charges, and magnetic forces acting upon other magnets or magnetic materials .
FILAMENT - The cathode of a thermionic tube, usually a wire or ribbon,
which is heated by current passing through it .
FILE - A collection of related records; for example, a payroll file. Any
collection of records holding similar data or transactions that are stored together to
permit systematic access and modification.
FILE, MASTER - The file that contains all the data records in up-to-date
form. It is a main reference file of relatively more permanent information, which is
usually updated periodically.
FILM ICs - Conductive or nonconductive material deposited on a glass or
ceramic substrate. Used for passive circuit components, resistors, and capacitors .
FILTER - A selective network of resistors, capacitors, and inductors that
offers comparatively little opposition to certain frequencies, while blocking or
attenuating other frequencies .
FINAL POWER AMPLIFIER (FPA) - The final stage of amplification in a
transmitter .
FIRMWARE - A set of program instructions, a microprogram, permanently
stored in read-only memory.
FIRST DETECTOR - See MIXER .
FIXED BIAS - A constant value of bias voltage .
FIXED RESISTOR - A resistor having a definite resistance value that cannot
be adjusted .
FIXED SPARK GAP - A device used to discharge the pulse-forming network. A
trigger pulse ionizes the air between two contacts to initiate the discharge .
FLAT LINE - A transmission line that has no standing waves. This line
requires no special timing devices to transfer maximum power .
FLAT PACK - An IC package .
FLAT PANEL DISPLAY - A display device that consists of a grid of
electrodes in a flat, gas-filled panel. The image can persist for a long period of time
without refresh.
FLEMING VALVE - An earlier name for a diode, or a two-electrode vacuum
tube used as a detector .
FLEXIBLE COAXIAL LINE - A line made with an inner conductor that consists
of flexible wire insulated from the outer conductor by a solid, continuous insulating
material .
FLIP CHIP - A monolithic IC packaging technique that eliminates the need
for bonding wires .
FLIP-FLOP - A device having two stable states and two input terminals (or
types of input signals), each of which corresponds with one of the two states. The circuit
remains in either state until caused to change to the other state by application of a
voltage pulse. A similar bistable device with an input that allows it to act as a
single-stage binary counter .
FLOPPY DISK - (See disk.)
FLOWCHART - A graphic representation of the processing steps (logic) of a
program (a program flowchart) or the inputs, outputs, and processing steps of a system (a
systems [data] flowchart). The graphic representation uses symbols to represent operations
and directional lines to indicate sequence and direction of flow.
FLUTTER - (See wow.)
FLUX - (1) In electrical or electromagnetic devices, a general term used
to designate collectively all the electric or magnetic lines of force in a region . (2) A
solution that removes surface oxides from metals being soldered .
FLUX DENSITY - The number of magnetic lines of force passing through a
given area .
FLYWHEEL EFFECT - The ability of a resonant circuit to operate
continuously because of stored energy or energy pulses .
FM - (See frequency modulation.)
FOCUSING ANODE - An electrode of a CRT that is used to focus the electrons
into a tight beam .
FOLDED DIPOLE - An ordinary half-wave antenna (dipole) that has one or
more additional conductors connected across the ends parallel to each other .
FORBIDDEN BAND - The energy band in an atom lying between the conduction
band and the valence band. Electrons are never found in the forbidden band but may travel
back and forth through it. The forbidden band determines whether a solid material will act
as a conductor, a semi-conductor, or an insulator .
FORMAT - The arrangement or layout of data in or on a data medium.
FORTRAN (FORmula TRANslator) - A high-level programming language for
scientific and mathematical applications.
FORWARD AGC - The type of agc that causes an amplifier to be driven
towards saturation .
FORWARD BIAS - An external voltage that is applied to a PN junction in the
conducting direction so that the junction offers only minimum resistance to the flow of
current. Conduction is accomplished by majority current carriers (holes in P-type
material; electrons in N-type material) .
FORWARD RESISTANCE - The smaller resistance value observed when you are
checking the resistance of a semiconductor .
FOSTER-SEELEY DISCRIMINATOR - A circuit that uses a double-tuned rf
transformer to convert frequency variations in the received fm signal to amplitude
variations. Also known as a phase-shift discriminator .
FOUR-ELEMENT ARRAY - An antenna array with three parasitic elements and
one driven element .
FRAMING - The process of synchronizing a facsimile receiver to a
transmitter. This allows proper picture reproduction .
FREE CHARGES - Those electrons that can be moved by an externally applied
voltage .
FREE-SPACE LOSS - The loss of energy of radio waves caused by the
spreading of the wavefront as it travels from the transmitter .
FREQUENCY (f) - (1) The number of complete cycles per second existing in
any form of wave motion, such as the number of cycles per second of an alternating current
. (2) The rate at which the vector that generates a sine wave rotates .
FREQUENCY COMPENSATION NETWORK - Circuit modification used to improve or
broaden the linearity of its frequency response .
FREQUENCY CUTOFF - The frequency at which the filter circuit changes from
an action of rejecting the unwanted frequencies to an action of passing the desired
frequencies. Conversely, the point at which the filter circuit changes from an action in
which it passes the desired frequencies to an action in which it rejects the undesired
frequencies .
FREQUENCY-DETERMINING NETWORK - A circuit that provides the desired
response (maximum or minimum impedance) at a specific frequency .
FREQUENCY DEVIATION - Refers to the difference between the carrier
frequency of an fm signal and the instantaneous frequency of its modulated wave.
FREQUENCY DIVERSITY - Transmitting (and receiving) of radio waves on two
different frequencies simultaneously .
FREQUENCY-DIVISION MULTIPLEXING - Multiplexing that transmits and receives
the full 360 degrees of each sine wave .
FREQUENCY DOMAIN - A plot of frequency versus amplitude as shown by a
spectrum analyzer display.
FREQUENCY METER - A meter used to measure the frequency of an ac signal .
FREQUENCY MODULATION (fm) - Angle modulation in which the modulating
signal causes the carrier frequency to vary. The amplitude of the modulating signal
determines how far the frequency changes, and the frequency of the modulating signal
determines how fast the frequency changes .
FREQUENCY MULTIPLIERS - Special rf power amplifiers that multiply the
input frequency .
FREQUENCY RESPONSE - (I) The ability of a component or device to operate
over a portion of the frequency spectrum. (2) In reference to test equipment, that portion
of the frequency spectrum that the test equipment is capable of sensing and measuring
accurately.
FREQUENCY-RESPONSE CURVE - A curve showing the output of an amplifier (or
any other device) in terms of voltage or current plotted against frequency with a
fixed-amplitude input signal .
FREQUENCY SCANNING - Varying the output frequency to achieve electronic
scanning .
FREQUENCY-SHIFT KEYING (fsk) - Frequency modulation somewhat similar to
continuous-wave (cw) keying in AM transmitters. The carrier is shifted between two
differing frequencies by opening and closing a key .
FREQUENCY SPECTRUM - In a radar, the entire range of frequencies contained
in an rf pulse or signal .
FREQUENCY STABILITY - Refers to the ability of an oscillator to accurately
maintain its operating frequency .
FREQUENCY SYNTHESIS - A process that uses hetrodyning and frequency
selection to produce a signal .
FREQUENCY SYNTHESIZER - (1) A frequency source of high accuracy . (2) A
bank of oscillators in which the outputs can be mixed in various combinations to produce a
wide range of frequencies .
FRONT-TO-BACK RATIO - The ratio of the energy radiated in the principal
direction compared to the energy radiated in the opposite direction .
FULL-DUPLEX CHANNEL - A channel that provides for simultaneous
transmission in both directions, such as the telephone.
FULL-WAVE RECTIFIER - A circuit that uses both positive and negative
alternations in an alternating current to produce direct current .
FULL-WAVE VOLTAGE DOUBLER - Consists of two half-wave voltage rectifiers
and is used to reduce the output ripple amplitude .
FUNCTION - A specific purpose of an entity; its characteristic action .
FUNDAMENTAL FREQUENCY - The basic frequency or first harmonic frequency .
FUSED-ALLOY JUNCTION - See ALLOYED-JUNCTION .
