18WuD2x

CMRR • coaxial capacitor 121
CMRR See COMMON-MODE REJECTION RATIO.
CMV See COMMON-MODE VOLTAGE.
C network A circuit with three impedances connected
in series, the free leads being connected to
a pair of terminals and the two internal junctions,
to another pair of terminals.
Co Symbol for COBALT.
C o Symbol for OUTPUT CAPACITANCE.
coalesce In computer operations, to create one file
from several.
coarse adjustment Adjustment of a quantity in
large increments. Compare FINE ADJUSTMENT.
coarse-chrominance primary See Q SIGNAL.
coastal bending A change in the horizontal direction
of a line-of-sight radio wave when it crosses a
coastline.
coast station In the Maritime Mobile Radio Service,
a land station that communicates with shipboard
stations.
coating 1. The application of a substance to another
substance by means of electroplating, electrophoresis,
or similar process, for the purpose of
protecting the material, isolating it from the environment,
or improving the conductivity of an
electrical connection to some other object. 2. The
magnetic material on a recording tape. 3. In a
computer system, the magnetic material on a
magnetic diskette or hard disk.
coating thickness On magnetic tape or magnetic
disks, the depth of the magnetic coating applied
to the base.
coax Abbreviation of COAXIAL CABLE or COAXIAL
LINE.
coaxial antenna A half-wave vertical antenna that
is center-fed by coaxial cable. The cable runs upward
through a 1⁄4-wave section of tubing that
composes the lower half of the antenna. The
outer conductor of the cable is connected to this
tubing through a shorting disk at the top. The inner
conductor of the cable is connected to a 1 ⁄4-
wave vertical radiator that is insulated from, and
that extends upward from the top of, the lower
section.
coaxial cable An unbalanced cable consisting of
two concentric conductors: an inner wire and an
outer, braided sleeve. The inner and outer conductors
are separated by a dielectric, usually
solid or foamed polyethylene. The outer conductor
is generally grounded while the inner conductor
carries the signals. This cable is used in
community-antenna television (CATV) networks,
and as a transmission line connecting antennas
to radio transmitters, receivers, and transceivers
at low, medium, high, and very-high frequencies.
It is also used in some high-fidelity sound systems—especially
to connect microphones, compact-disc
players, tape players, tuners, and
speakers to audio amplifiers.
coaxial cable
(From left to right: insulating jacket,
woven outer conductor, low-loss insulating
sleeve, inner conductor.)
Characteristics of
prefabricated coaxial transmission lines.
Characteristic
impedance, Velocity Outside Picofarads
Type (ohms) factor dia. (in.) per foot
RG-8/U 52 0.66 0.41 29.5
RG-9/U 51 0.66 0.42 30.0
RG-11/U 75 0.66 0.41 20.6
RG-17/U 52 0.66 0.87 29.5
RG-58/U 54 0.66 0.20 28.5
RG-59/U 73 0.66 0.24 21.0
RG-174/U 50 0.66 0.10 30.8
hard line 50 0.81 0.50 25.0
( 1 /2-inch) 75 0.81 0.50 16.7
hard line 50 0.81 0.75 25.0
( 3 /4-inch) 75 0.81 0.75 16.7
coaxial capacitor 1. A somewhat uncommon, but
highly effective, capacitor that uses two telescoping
sections of tubing. It works because there is a
certain effective surface area between the inner
and the outer tubing sections. A sleeve of plastic
dielectric is placed between the sections of tubing.
This allows the capacitance to be adjusted by
sliding the inner section in or out of the outer section.
Coaxial capacitors are especially useful in
antenna systems for tuning and/or impedance
matching. Their values are generally from a few