18WuD2x

286 firing circuit • fixed-frequency oscillator
firing circuit Any circuit, such as a phase shifter,
that permits adjustment of the firing angle of a
silicon-controlled rectifier (SCR) or similar device,
or which delivers the required pulse or other signal
to initiate firing.
firmware 1. Programs (software) in nonvolatile
computer memory [e.g., in a read-only memory
(ROM), that can only be changed by replacement
with an alternate unit]. 2. Unalterable internal
interconnections that determine what a computing
device or system can do. Also called MICRO-
PROGRAM.
first detector In a superheterodyne circuit, the
signal frequency detector. Compare SECOND DE-
TECTOR.
first filter capacitor The input capacitor in a capacitor-input
power-supply filter.
first Fresnel region A portion of a directional
transmitted electromagnetic ray, shaped generally
like a paraboloid with the apex at the transmitter
and the axis in the direction of
transmission. Any point in the first Fresnel zone
is in such a position that the sum of the lengths
of the paths from the point to the receiver, and
the point to the transmitter, is no greater than
0.5 wavelength more than the distance from the
transmitter to receiver.
first harmonic The fundamental frequency in a
complex waveform from which multiples are generated.
first-in/first-out Acronym, FIFO. A read-write
memory commonly used as a buffer to smooth
out the flow of data bits in a digital system. The
output bits are in the same order (sequence) as
the input bits. If a data bit x goes into the FIFO
before data bit y, then x will always emerge from
the FIFO before y. Compare PUSHDOWN STACK.
first-in/last-out See PUSHDOWN STACK.
first law of thermodynamics Quantities of heat
can be converted into mechanical work, and vice
versa. Also see MECHANICAL EQUIVALENT OF
HEAT.
first level address See ABSOLUTE ADDRESS.
first selector The selector that responds to the
first-digit dial pulses when a telephone number is
called.
fishbone antenna An untuned, wideband directional
antenna of the general end-fire type. Consists
of a number of collector antennas, each
capacitively coupled to the resistor-terminated
transmission line in collinear pairs. It is so
called from its resemblance to the skeleton of a
fish.
fishpaper A chemically treated, vulcanized-fiber
paper used for electrical insulation.
fish pole A microphone boom that can be held in
the hand.
fist In radiotelegraphy and wire telegraphy, an operator’s
manual sending style.
fitting A device intended to mechanically fasten a
wire or cable in place.
Terminating
resistor
Collector antennas
Transmission line
fishbone antenna
To receiver
five-element code A five-impulse telegraph code
that describes a character (e.g., Baudot, which
also includes start and stop elements).
five-layer device A semiconductor device containing
four pn junctions. Examples: diac and triac.
five-level code A teletype code that utilizes five binary
elements to define a character.
fix 1. In direction finding, the point at which two
lines of direction intersect. 2. In electronics maintenance,
to repair successfully. 3. To subject an
in-process circuit board to a solution or other
medium to stop a photographic action permanently.
Also, the solution in which such photosensitive
materials can be immersed to halt
development.
fixed bias Bias voltage or current supplied from a
fixed external source (such as a battery or power
supply) independent of the operation of the biased
device. Compare AUTOMATIC BIAS.
fixed block length Blocks of data having a fixed
number of words or characters, as required because
of hardware limitations or a program instruction.
Compare VARIABLE BLOCK LENGTH.
fixed capacitor A nonadjustable capacitor (i.e.,
one having a single unalterable value).
fixed component Any component (e.g., a capacitor,
inductor, or resistor that has one unalterable
value).
fixed contact The stationary contact in a relay or
switch. Compare MOVABLE CONTACT.
fixed-crystal detector A simple crystal detector in
which the point of the contact wire is permanently
placed in contact with a sensitive spot on
the surface of the crystal.
fixed field Fields in records organized so that
those containing similar information in each
record are the same length and in the same relative
position in the record. Compare VARIABLE
FIELD.
fixed form coding The coding of source languages
so that each part of the instruction is in a fixed
field.
fixed-frequency amplifier An amplifier that is
pretuned to operate on one frequency, or in a relatively
narrow band of frequencies.
fixed-frequency oscillator An oscillator that is
preset to operate on one frequency. Such an os-