FREQUENCYThe 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 DETECTORAn 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 FREQUENCIESIntegral multiples of a fundamental frequency
HETERODYNE DETECTIONThe use of an af voltage to distinguish between available
signals. The incoming cw signal is mixed with locally generated oscillations to give an af
HETERODYNINGMixing two frequencies across a nonlinear impedance.
HIGH-LEVEL MODULATIONModulation produced in the plate circuit of the last radio
stage of the system.
INSTANTANEOUS AMPLITUDEThe 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 CLICKSInterference in the form of "clicks" or "thumps" caused by the sudden
application or removal of power.
KEY-CLICK FILTERSFilters used in keying systems to prevent key-click interference.
KEYING RELAYSRelays used in high- power transmitters where the ordinary hand key
cannot accommodate the plate current without excessive arcing.
LINEAR IMPEDANCEAn impedance in which a change in current through a device changes
in direct proportion to the voltage applied to the device.
LOW-LEVEL MODULATIONModulation produced in an earlier stage than the final.
LOW-PASS FILTERA method of demodulating pdm by averaging the voltage over pulse and
LOWER SIDEBANDAll difference frequencies below that of the carrier.
MACHINE KEYINGA method of cw keying using punched tape or other mechanical means
to key a transmitter.
MAGNETIC MICROPHONEA 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.
MARKAn 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.