Page 94 - The Illustrated Dictionary of Electronics

5059F-pB_56-92 4/9/01 4:45 PM Page 79

blocking oscillator • BNC 79

ence. 2. A parasitic oscillation in a radio trans-
mitter. 3. In broadcasting, a statement in which a
radio or television announcer makes an embar-
rassing error or breach of etiquette.
blow The opening of a fuse or circuit breaker as a
result of excessive current.
blower A fan used to remove heat from electronic
circuits. These are often used in tube-type radio-
frequency (RF) power amplifiers, where much
heat is generated, and in computers to cool the
microprocessor and surrounding components.
blowout 1. An alternate term for BURNOUT. 2. The
forceful opening of a circuit breaker. 3. The extin-
guishing of an arc.
blowout coil An electromagnet that provides a field
to extinguish an arc.
blowout magnet A permanent magnet that pro-
vides a field to extinguish an arc.
blst Abbreviation of ballast.
blue-beam magnet In a color television picture-
tube assembly using three electron guns, a small
permanent magnet to adjust the static conver-
gence of the beam for blue phosphor dots.
blue box An accessory device (sometimes unlaw-
blocking oscillator An oscillator that turns itself fully used) that generates tones that switch a tele-
off after one or more cycles. It does this as a re- phone circuit in the placing of calls.
sult of an accumulation of negative charge on its blue glow 1. In a neon lamp, a bluish light that
input electrode (base of a bipolar transistor or results from high-voltage arcing. 2. The normal
gate of a field-effect transistor). The action is color of the gas discharge in an argon glow
repetitive. In the self-pulsing type of blocking os- lamp. 3. The bluish glow between anode and
cillator, a series of pulses consisting of trains of cathode of a gassy vacuum tube. 4. The normal
sine waves with intervening spaces is generated. color of the discharge that fills a mercury-vapor
In the single-swing type of blocking oscillator, the tube.
output consists of a series of single cycles with blue gun The electron in a three-gun color picture
long intervals between them. tube, the beam from which strikes the blue phos-
blocking oscillator synchronization 1. In the phor dots.
BLOCKING OSCILLATOR used in the vertical de- blueprint 1. A type of contact-print reproduction
flection circuit of a television receiver, the oscilla- in which a sheet of sensitized paper is exposed to
tor is synchronized with vertical sync pulses an image on a translucent or transparent film,
arriving in the video signal. 2. Synchronization of under strong light, and is then developed and
the repetition rate of any blocking oscillator with fixed. Although this process is still used to repro-
a suitable external control signal. duce electronic illustrations and typescripts, it
blocking system In a telephone system, a method has been superseded largely by other (dry) pro-
of dealing with the condition of having more sub- cesses. 2. Loosely, any plan or design for the de-
scribers than connection paths. Allocation is velopment of a system.
made on a demand basis. If all channels are in blue restorer In a three-gun color television cir-
use, it is impossible to make new calls. This pre- cuit, the dc restorer in the blue channel.
vents excessive degradation of the quality of ex- blue ribbon program A computer program that
isting connections. has been hand-prepared and debugged com-
block length The number of characters, bits, or pletely before its first computer run.
words that compose a defined unit word or char- blue video voltage The signal voltage presented to
acter group. the grid of the blue gun of a three-gun color pic-
block transfer The conveyance of a word or char- ture tube.
acter grouping in a computer register to another blurring 1. BLOOMING. 2. A defocusing of a televi-
register or a peripheral device. sion picture or oscilloscope trace. 3. An obscur-
blooming On a cathode-ray-tube (CRT) screen, an ing of a signal by echoes or trailing (e.g., the slow
enlargement of the electron-beam spot, caused by decrement of a Morse code signal element).
poor focusing. This results in poor image B-minus Also called B-negative. The negative ter-
resolution. minal of a B-power supply.
blooper 1. A radio receiver that is in oscillation, BNC Abbreviation of bayonet Neill-Concelman. A
and is transmitting a signal that causes interfer- type of coaxial connector that can be quickly con-