AI-5
PHASE or PHASE ANGLE—The angle that exists between the starting point of a vector and its
position at that instant. An indication of how much of a cycle has been completed at any
given instant in time.
PHASE-SHIFT DISCRIMINATOR—See Foster-Seeley discriminator.
PHASE-SHIFT KEYING—Similar to ON-OFF cw keying in AM systems and frequency-shift
keying in fm systems. Each time a mark is received, the phase is reversed. No phase reversal
takes place when a space is received.
PLATE KEYING—A keying system in which the plate supply is interrupted.
PLATE MODULATOR—An electron-tube modulator in which the modulating voltage is
applied to the plate circuit of the tube.
POSITIVE ALTERNATION—That part of a sine wave that is above the reference line.
PULSE DURATION (pd)—The period of time during which a pulse is present.
PULSE MODULATION—A form of modulation in which one of the characteristics of a pulse
train is varied.
PULSE WIDTH (pw)—The period of time during which a pulse occurs.
PULSE—A surge of plate current that occurs when a tube is momentarily saturated.
PULSE-AMPLITUDE MODULATION (pam)—Pulse modulation in which the amplitude of
the pulses is varied by the modulating signal.
PULSE-CODE MODULATION (pcm)—A modulation system in which the standard values of
a quantized wave are indicated by a series of coded pulses.
PULSE-DURATION MODULATION (pdm)—Pulse modulation in which the time duration
of the pulses is changed by the modulating signal.
PULSE-FORMING NETWORK (pfn)—A circuit used for storing energy. Essentially a short
section of artificial transmission line.
PULSE-FREQUENCY MODULATION (pfm)—Pulse modulation in which the modulating
voltage varies the repetition rate of a pulse train.
PULSE-POSITION MODULATION (ppm)—Pulse modulation in which the position of the
pulses is varied by the modulating voltage.
PULSE-REPETITION FREQUENCY—The rate, in pulses per second, at which the pulses
occur.
PULSE-REPETITION TIME (prt)—The total time for one complete pulse cycle of operation
(rest time plus pulse width).
PULSE-TIME MODULATION (ptm)—Pulse modulation that varies one of the time
characteristics of a pulse train (pwm, pdm, ppm, and pfm).
PULSE-WIDTH MODULATION (pwm)—Pulse modulation in which the duration of the
pulses is varied by the modulating voltage.
