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QC • quad 567
QC Abbreviation of QUALITY CONTROL.
QCE Abbreviation of QUALITY-CONTROL ENGI-
NEERING or QUALITY-CONTROL ENGINEER.
Q channel In American (NTSC) color television, the
508-kHz-wide green-magenta color information
transmission band.
QCT Abbreviation of QUALITY-CONTROL TECHNI-
CIAN.
QCW In the local oscillator and associated circuitry
of a color television receiver, a 3.85-MHz CW signal
of Q PHASE.
QCW signal In a color television receiver, the component
of the chrominance signal that is 90 degrees
out of phase with the in-phase component.
Q demodulator In a color television receiver, the
demodulator that combines the chrominance signal
and the color-burst oscillator signal to recover
the Q signal (see Q SIGNAL, 2).
QED 1. Abbreviation of QUANTUM ELECTRODY-
NAMICS. 2. Abbreviation of quod erat demonstrandum,
Latin for “which was to be
demonstrated.” Also, Q.E.D. Often written at the
conclusions of valid logical proofs and derivations.
Q factor See Q.
QFM Abbreviation of QUADRATURE MODULA-
TION.
QM Abbreviation of QUADRATURE MODULATION.
Q-matching section A linear radio-frequency
impedance-matching transformer consisting of
two straight, rigid, parallel metal conductors that
are used to match a feeder to an antenna. The
section is 1 ⁄4 wavelength long at the operating frequency.
The diameters and center-to-center
spacing of the conductors are such that the characteristic
impedance of the matching section is
equal to the geometric mean of the feeder characteristic
impedance and the radiation resistance of
the radiator. Also see Q ANTENNA and QUAR-
TER-WAVELENGTH MATCHING STUB.
Q meter A usually direct-reading instrument for
determining the Q of a capacitor, inductor, or inductance-capacitance
(LC) circuit. Most Q meters
are operated at radio frequencies, but audiofrequency
instruments are available.
Q modulation Amplitude modulation obtained by
varying the effective Q of a radio-frequency tank
circuit in step with a modulating component. See
ABSORPTION MODULATION.
QMQB Abbreviation of quick make/quick break.
Q multiplier A positive-feedback (regenerative)
amplifier that increases the effective Q of a tuned
circuit, and thereby sharpens its response, when
its input is connected across the tuned circuit.
Q output The reference output of a flip-flop.
Q phase A color-television carrier signal that is 147
degrees out of phase with the color subcarrier.
Q point The point or points at which a load line intersects
a device characteristic (such as the collector
curve of a transistor or plate curve of a
tube) and that identifies the quiescent operating
point.
Reverse
Q point
Reverse
voltage
Reverse
load line
Forward
current
Reverse
current
Forward voltage
Forward Q point.
Q points on diode characteristic
Forward
load line
QRD Abbreviation of QUADRATIC RESIDUE DIF-
FUSOR.
Q-section transformer See Q-MATCHING SEC-
TION.
Q signal In color television, the quadrature component
of the chrominance signal, equal to +0.48(R-
Y) and to +0.41(B-Y), where B is the blue camera
signal, R is the red camera signal, and Y is the luminance
signal.
Q signals A set of three-letter groups, each beginning
with the letter Q, used for simplified telegraph
and radiotelegraph communication, and
sometimes rapid voice communication (in radiotelephony).
Each signal represents a commonly
used phrase or message.
QSL card A card verifying communication with, or
the reception of signals from, the station sending
the card. Such verification is common in the amateur
radio service and with some shortwave
broadcast and CB stations.
QSO Amateur radiotelegraph abbreviation for
TWO-WAY COMMUNICATION.
Q spoiler A device or circuit that produces Q
SPOILING in a laser.
Q spoiling The technique of inhibiting laser action
during an interval when an ion population excess
is pumped up. When the laser is subsequently
triggered by Q switching, a more powerful pulse
of light results than would be otherwise obtained.
Q switching A laser-switching action obtainable
with Kerr cells or rotating reflecting prisms,
which consists of holding the Q of the laser cavity
to a low value during an ion-population buildup,
then abruptly switching the Q to a higher value.
Q transformer See Q-MATCHING SECTION.
qty Abbreviation of QUANTITY.
quad 1. A combination of four components, such as
diodes, transistors, etc., in a single housing. The
components are usually carefully matched. 2. In a
cable, a combination of four separately insulated
conductors (sometimes, two twisted pairs) twisted