18WuD2x

68 beam-positioning magnet • beat marker
beam-positioning magnet In a three-gun color
television picture tube, a permanent magnet that
is used to position one of the electron beams correctly,
with respect to the other two.
beam power tube A tetrode or pentode vacuum
tube, in which special deflector plates concentrate
the electrons into beams in their passage from
cathode to plate. The beam action greatly increases
plate current at a given plate voltage. It is used in
some radio-frequency (RF) power amplifiers.
beam-rider control system A missile-guidance
system in which a control station sends a radio
beam to a missile. The beam is moved in such a
way that as the missile stays within the beam, it
hits the target.
beam-rider guidance 1. An aircraft landing guidance
system, in which the aircraft follows a radio
beam in its glide path. 2. The circuitry in a guided
missile using a beam-rider control system.
beam splitter A device used to divide a light beam
(as by a transparent mirror) into two components,
one transmitted and the other reflected;
hence, a BEAM-SPLITTING MIRROR.
beam splitting In radar, a method of calculating
the mean azimuth of a target from the azimuth at
which the target is first revealed by one scan, and
the azimuth at which the target information
ceases.
beam-splitting mirror In an oscilloscope-camera
system, a tilted, transparent mirror that allows
rays to pass horizontally from the oscilloscope
screen to the camera and to be reflected vertically
to the viewer’s eye.
beamwidth of antenna The angular width of the
main lobe of the pattern of radiation from a directional
antenna. Generally, it is measured be-
Half-power
width
tween the half-power points in the horizontal
plane. Occasionally, it is measured in the vertical
plane.
bearing The direction of an object or point expressed
in degrees within a 360° horizontal clockwise
boundary, with the center of the circle
serving as the observation point.
bearing resolution In radar operations, the minimum
horizontal separation of two targets, in degrees,
that permits the individual targets to be
displayed as two echoes, rather than one.
beat Any one of the series of pulsations constituting
a beat note, which results from heterodyning
one signal against another.
beat frequency Either of two frequencies f C1 and
f C2 resulting from the mixing of two signals of different
frequencies f A and f B . Frequency f C1 is the
sum of the two input frequencies; f C1 = f A + f B .
Frequency f C2 is the difference; f C2 = f A – f B when
f A is the higher of the two input frequencies.
beat-frequency oscillator Abbreviation, BFO. An
oscillator used to set up audible beat frequencies
with an incoming received signal and installed
in the intermediate-frequency (IF) stages
of a superheterodyne communications receiver.
For single-sideband (SSB) reception, the BFO is
set at the frequency of the received suppressed
carrier. In continuous-wave (CW) Morse code reception,
the BFO is set at a frequency that differs
from that of the incoming signal by about
400 to 1000 Hz. The resulting tone has an audio
frequency equal to the difference between the
BFO frequency and the received signal carrier
frequency. For reception of frequency-shiftkeyed
(FSK) signals, the BFO is set to such a frequency
that the resulting audio beat notes are
appropriate for the mark and space inputs of a
terminal unit or modem.
IF
amp.
Mixer
AF
amp.
From
previous
IF stage
BFO
beat-frequency oscillator
Audio
output
beamwidth of antenna
beating 1. Also called heterodyning. The combination
of signals of different frequencies resulting in
sum and difference frequencies. 2. The fluttering
noise heard when two audio tones, very close in
frequency and very similar in amplitude, are
emitted at the same time.
beat marker In the visual (oscilloscopic) alignment
of a tuned circuit, a marker pip that results from
the beat note between the sweep-generator signal
and the signal from a marker oscillator.