18WuD2x

288 flange focus • flattening
flange focus The focal length of a lens, based on
the distance from the mounting flange to the focal
plane.
flanging In sound systems, a means of obtaining
special effects using a COMB FILTER. Creates an
“extraterrestrial,” digitized sound. Commonly
used by rock music bands.
flanking Modification of the response of a selective
filter, resulting from the parallel connection of
two or more similar filters.
flap See DROP INDICATOR.
flap attenuator A waveguide attenuator consisting
of a sheet of resistance material inserted transversely
into the waveguide through a slot.
flare 1. The hyperbolic cross section of a horn antenna
or loudspeaker. 2. A transient or stationary
bright area with (usually) a central pip on the
screen of an otherwise blank oscilloscope or television
picture tube.
flare angle The gradual change in a waveguide’s
diameter over its length.
flare factor The angle at which the faces of a horn
speaker are curved or turned outward.
flaring constant Symbol, m. A number expressing
the degree of flare (see FLARE, 1) in a horn
antenna or loudspeaker. The value of m is equal
to 0.6931/d, where d is the distance along the
axis required for the cross-sectional area A of
the horn to double. If d is given in feet (ft), for example,
then A is in units of square feet (ft 2 ) and
m is in units of reciprocal feet (1/ft). If d is in
centimeters (cm), then A is in units of square
centimeters (cm 2 ) and m is in units of reciprocal
centimeters (1/cm).
flash 1. A photographic camera flash. 2. To vaporize
a metal (such as magnesium) in an electron
tube being evacuated, to absorb gases. 3.
Flashover.
flash arc In a vacuum tube, a sudden high-current
arc between cathode and plate at high plate voltages;
it can short-circuit the plate power supply.
flashback voltage The maximum inverse voltage
that causes the gas in a tube to ionize.
flash delay A device that automatically postpones
the operation of a FLASHTUBE until a predetermined
instant, such as the moment when a moving
object arrives at a particular point before a
camera.
flasher An electrical or electronic device or circuit
that flashes a light or a series of lights sequentially.
flasher LED A light-emitting diode (LED) that,
when connected to a low-voltage direct-current
(dc) source, emits light that flashes at a basic rate
of a few pulses per second.
flashlamp 1. See FLASHTUBE. 2. A small portable
light operated from self-contained cells; a flashlight
or lantern.
flashlight See FLASHLAMP, 2.
flash memory High-capacity, nonvolatile randomaccess
memory, used in some computers in place
of an electromechanical hard drive. This type of
memory allows a computer to store, access, and
run large data files or programs much faster than
is possible with a conventional hard drive. See
also NONVOLATILE MEMORY, RANDOM-
ACCESS MEMORY.
flashover The sudden discharge of electrical energy
between electrodes or conductors, often accompanied
by light; it is usually the result of
excessive voltage.
flashover voltage 1. The peak voltage at which
FLASHOVER occurs. 2. The voltage at which disruptive
discharge occurs between electrodes and
across the surface of an insulating material.
flash plating Electroplating in which a thin layer is
deposited quickly.
flash test Insulation testing by applying a higherthan-normal
voltage for a short time.
flashtube A straight or coiled glass tube filled with
gas and provided with electrodes. When a high
voltage is applied to the electrodes, the tube emits
a brilliant flash of light.
flat cable
Also called ribbon cable. A cable whose
flexible conductors are molded side by side in a
flexible, flat ribbon of plastic (such as polyethylene).
flat-compounded generator A compound-wound
generator whose windings are proportioned so that
the full-load and no-load voltages are identical.
flat fading Fading of a radio signal that occurs independently
of frequency; all frequency components
of the signal fade to the same extent at the
same time.
flat file A computer file containing unfolded documents.
flat frequency response Relatively equal response
to all fixed-point frequencies within a given spectrum,
exhibited by an amplifier or other circuit
that must transmit a band of frequencies.
flat line A transmission line in which there are no
standing waves, or for which the standing-wave
ratio is very low.
flat pack An integrated circuit package consisting
of a square or rectangular flat housing, with pins
projecting straight outward from the edges.
flat response A response characteristic in which
the dependent variable is substantially constant
over a specified range of values of the independent
variable. For example, in amplifier operation,
an output signal whose component
fundamental frequencies and their harmonics are
in the same proportion as those of the input signal
being amplified.
flat-ribbon line A transmission line (feeder) consisting
of two flexible conductors molded in a flexible,
flat ribbon of plastic, such as polyethylene.
Also called twinlead.
flattening
The leveling-off or blunting of a normally
peaked or curved response, often caused by
signal saturation within a circuit. Sine-wave clipping
is an example.