18WuD2x

chirp • chopper power supply 113
can go up or down in frequency. Chirp occurs because
of a change in the output impedance of an
oscillator as it is keyed. Modern code transmitters
do not exhibit significant chirp.
chirp modulation A form of modulation in which
the frequency of a signal is deliberately changed
in a systematic way. Used in some radar systems.
chirp radar A radar system that uses CHIRP MOD-
ULATION.
Chladni’s plates Conducting plates that are used
to evaluate the nature of a vibration in a solid material.
The plates are clamped to the material, and
sand is sprinkled on the surface. This produces
patterns that indicate the nature of the vibrations.
chlorinated diphenyl A synthetic organic substance
used as an impregnant in some oil-filled
capacitors.
chlorinated naphthalene See HALOWAX.
chlorine Symbol, Cl. A gaseous element of the
halogen family. Atomic number, 17. Atomic
weight, 35.453.
choke
1. To restrict or curtail passage of a particular
current or frequency by means of a discrete
component, such as a choke coil. 2. See CHOKE
COIL.
choke air gap A fractional-inch opening in the iron
core of a filter choke, usually filled with wood or
plastic. The gap prevents saturation of the core
when the choke coil carries maximum rated direct
current.
choke coil 1. A large-value inductor that provides
a high impedance to alternating current (ac),
while offering virtually no opposition to direct
current (dc). 2. In radio-frequency (RF) applications,
an inductor that provides a high
impedance to RF signals while showing low
impedance for audio-frequency (AF) signals and
direct currents (dc).
choke-coupled modulation An amplitudemodulation
(AM) scheme, in which the modulator
is coupled to the radio-frequency (RF) amplifier
through a shared iron-core choke coil.
choke flange At the end of a waveguide, a flange in
which a groove forms a CHOKE JOINT.
choke-input filter A filter whose input component
is an inductor (choke). The choke-input powersupply
filter is distinguished by its superior
voltage regulation, compared with the
CAPACITOR-INPUT FILTER.
choke joint A joint connecting two waveguide sections
and permitting efficient energy transfer
without requiring electrical contact with the inside
wall of the waveguide.
chopped dc See INTERRUPTED DC.
chopped mode In a single-gun cathode-ray-tube
(CRT) oscilloscope, a technique for sequentially
displaying several signals that are not referenced
to the oscilloscope sweep.
chopped signal An ac or dc signal that is periodically
interrupted, as by means of a CHOPPER.
+
Pulsating
dc input
−
Filter
choke
Filter
capacitor
Smoothed
dc output
chopper A device or circuit that interrupts a direct
current (dc) at some predetermined rate. Ideally,
such a device is characterized by distinct on and
off operation.
chopper amplifier A circuit that amplifies the output
of a CHOPPER. Used in conjunction with a
CHOPPER CONVERTER in dc amplification.
chopper converter A device that interrupts a direct
current (dc), and changes it to a pulsating,
rectangular-wave current or voltage that can be
handled by a stable ac amplifier and rectified to
supply amplified dc.
chopper power supply Also called power inverter.
A circuit that delivers high-voltage ac from a dc
source. The input is typically 12 volts dc, and the
output is usually 117 volts rms ac. These devices
facilitate the use of small appliances such as
computers, television sets, and communications
radios in portable and mobile environments. The
output of a low-cost power inverter is generally
not a good sine wave. More sophisticated inverters
produce good sine waves and have a frequency
close to 60 Hz.
+
choke-input filter
+
−