AI-3
FREQUENCY—The rate at which the vector that generates a sine wave rotates.
FREQUENCY-SHIFT KEYING (fsk)—Frequency modulation somewhat similar to
continuous-wave (cw) keying in AM transmitters. The carrier is shifted between two
differing frequencies by opening and closing a key.
GATED-BEAM DETECTOR—An fm demodulator that uses a special gated-beam tube to
limit, detect, and amplify the received fm signal. Also known as a quadrature detector.
HARMONIC FREQUENCIES—Integral multiples of a fundamental frequency
HETERODYNE DETECTION—The use of an af voltage to distinguish between available
signals. The incoming cw signal is mixed with locally generated oscillations to give an af
output.
HETERODYNING—Mixing two frequencies across a nonlinear impedance.
HIGH-LEVEL MODULATION—Modulation produced in the plate circuit of the last radio
stage of the system.
INSTANTANEOUS AMPLITUDE—The amplitude at any given point along a sine wave at a
specific instant in time.
INTERMEDIATE POWER AMPLIFIER (ipa)—The amplifier between the oscillator and
final power amplifier.
KEY CLICKS—Interference in the form of "clicks" or "thumps" caused by the sudden
application or removal of power.
KEY-CLICK FILTERS—Filters used in keying systems to prevent key-click interference.
KEYING RELAYS—Relays used in high- power transmitters where the ordinary hand key
cannot accommodate the plate current without excessive arcing.
LINEAR IMPEDANCE—An impedance in which a change in current through a device changes
in direct proportion to the voltage applied to the device.
LOW-LEVEL MODULATION—Modulation produced in an earlier stage than the final.
LOW-PASS FILTER—A method of demodulating pdm by averaging the voltage over pulse and
no-pulse time.
LOWER SIDEBAND—All difference frequencies below that of the carrier.
MACHINE KEYING—A method of cw keying using punched tape or other mechanical means
to key a transmitter.
MAGNETIC MICROPHONE—A microphone in which the sound waves vibrate a moving
armature. The armature consists of a coil wound on the armature and located between the
pole pieces of a permanent magnet. The armature is mechanically linked to the diaphragm.
MARK—An interval during which a signal is present. Also the presence of an rf signal in cw
keying. The key-closed condition (presence of data) in communications systems.
