18WuD2x

distance mark • distributed component 203
distortion tolerance The maximum amount of
distortion that can be present in a signal without
making it useless. This varies over wide limits.
The maximum harmonic distortion that might be
acceptable in a high-fidelity sound system could
be less than 0.1% total, whereas in some applications
of ac power, 10% would be acceptable.
distress frequency A radio frequency on which an
emergency signal is transmitted. Ships at sea and
aircraft over the sea use 500 kHz (by international
agreement). In Citizen Band communications,
channel 9 has been set aside for emergency
use.
distress signal A signal indicating that trouble exists
at the transmitting station and imploring aid
from the recipient. The international radiotelegraph
distress signal is the three-letter combination
SOS; the international radiotelephone
distress signal is the word mayday, the phonetic
equivalent of the French m’aidez (help me).
distributed Existing over a measurable interval,
area, or volume; not concentrated in a single
place or places.
distributed amplifier A wideband, untuned amplifier
whose active devices are spaced (distributed)
along parallel, artificial delay lines
consisting of coils that act in combination with
the input and output capacitances of the active
devices. Adding active devices to the lineup increases
the gain. Commonly used as preamplifiers
for television receivers.
distributed capacitance Symbol, C d . Capacitance
that is dispersed throughout a component or system,
rather than being lumped in one place. An
example is the distributed capacitance of a coil.
distributed component An electrical property that
is spread throughout a circuit or device, rather
than being concentrated at one point, as in a discrete
component. For example, DISTRIBUTED
CAPACITANCE and DISTRUBUTED INDUC-
TANCE are spread along the length of a transmission
line. Another example is the DISTRIBUTED
RESISTANCE of a wire coil. Distributed compodistance
mark On a radar screen, a mark indicating
the distance from the radar set to the target.
distance measurement Also called ranging. A
method or system that allows a robot to navigate
in its environment. It also allows a central computer
to track the locations of robots under its
control. Can use radar, sonar, visible light, or infrared.
distance-measuring equipment In radionavigation,
a system that measures the distance of the
interrogator to a transponder beacon in terms of
the transmission time to and from the beacon.
distance protection The use of a protective device
within a specified electrical distance along a circuit.
distance relay In circuit protection, a relay that
operates to remove power when a fault occurs
within a predetermined distance along the circuit.
distance resolution 1. Qualitatively, the ability of
a ranging system to differentiate between two objects
or beacons that are almost, but not quite,
the same distance away. See RANGING. 2.
Quantitatively, the minimum radial separation of
objects or beacons necessary for a ranging
system to tell them apart. 3. For two targets
having the same azimuth bearing, the minimum
difference in range for which a radar display
renders them as distinct blips.
distant control See REMOTE CONTROL.
distorted-drive multiplier A frequency multiplier
whose excitation signal is a peaked wave that has
been predistorted to decrease the angle of flow in
the device, thus increasing its efficiency.
distorted nonsinusoidal wave A nonsinusoidal
wave whose ideal shape (square, rectangular,
sawtooth, etc.) has been altered.
distorted sine wave A wave that is approximately
of sinusoidal shape (i.e., it is not an exact plot of a
sine wave because of the presence of harmonics).
distortion 1. Deformation of a signal waveform. 2.
The additional deformation of a signal exhibiting
a less-than-ideal waveshape when it passes
through a circuit. Some distortion originates
within the signal generator itself; other forms result
from circuits and devices transmitting the
signal. 3. Any degradation in the quality of a
high-fidelity audio signal. 4. See TOTAL HAR-
MONIC DISTORTION.
distortionless 1. Having no distortion. 2. Having a
propagation velocity that does not depend on frequency.
distortion meter An instrument for measuring
harmonic distortion. It consists of a highly selective
band-rejection filter (notch filter) that removes
the fundamental frequency of the signal
under test, and a sensitive voltmeter that can be
switched between the filter input and the filter
output. The distortion percentage is determined
from the ratio between filter-output and filterinput
voltages.
Input
Notch
filter
distortion meter
Voltmeter