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heat transfer • helical antenna 335
Radiation
Convection
Heatsink
Heat-generating
components
heatsink
Radiation
Chassis
heat transfer The movement of heat from one
point to another by absorption, conduction, convection,
or radiation.
heatronic Pertaining to the heating of a dielectric
material subjected to a high voltage.
heat unit 1. See BRITISH THERMAL UNIT. 2. See
CALORIE. 3. See KELVIN.
heat waves See INFRARED RAYS.
heat writer See THERMAL RECORDER.
Heaviside-Campbell bridge A form of mutualinductance
bridge. Mutual inductance is determined
without regard to the operating frequency.
Heaviside layer See KENNELLY-HEAVISIDE
LAYER.
heavy hydrogen An isotope of hydrogen. The term
is applied to deuterium, whose nucleus consists
of one proton and one neutron, and also to tritium,
whose nucleus consists of one proton and
two neutrons.
heavy metal A metal having a specific gravity of
5.0 or higher. Examples: iron (7.85 to 7.88), lead
(11.3), nickel (8.6 to 8.9), mercury (13.6), platinum
(21.4).
heavy water Formula, D 2 O. Water in which deuterium
(HEAVY HYDROGEN), rather than ordinary
hydrogen has combined with oxygen.
hecto- Abbreviation, h. A prefix meaning hundred(s),
(i.e., 10 2 ).
hectometric wave An electromagnetic field whose
wavelength is on the order of hundreds of meters
(i.e., at least 100 meters, but less than 1000 meters).
The frequency ranges from 300 kHz to 3
MHz.
hectowatt Abbreviation, hW. A unit of power equal
to 100 watts. Seldom used; power in this range is
usually expressed in terms of the WATT or the
KILOWATT.
heelpiece A part of an electronic relay that provides
mechanical support for the armature.
Hefner candle A unit of luminous intensity equal
to 0.9 candela; the standard (German) is the
HEFNER LAMP.
Hefner lamp A standard light source whose luminous
intensity is 0.9 candela. It burns amyl acetate
(banana oil) and its flame has been the
standard of the HEFNER CANDLE, a unit of luminous
intensity devised in Germany. Also see
CANDLE POWER and LUMINOUS INTENSITY.
height control In a television receiver circuit, the
potentiometer or rheostat that controls the vertical
dimension of the picture by varying the amplitude
of vertical scanning pulses.
height finder An altitude-measuring radar system.
height-position indicator Abbreviation, HPI. A
radar displaying the height of a target, its angular
elevation, and the slant range.
Heil oscillator An oscillator based on a special
tube consisting of a heated cathode, first anode,
metal cylinder, and second anode. Electrons
emitted by the cathode pass through a hole in the
first anode and become a beam, which passes
through the cylinder and strikes the second anode
(collector). Electron bunching in the cylinder
causes energy to be transferred to a tank circuit
between the cylinder and anodes.
Cathode
Anode 1
−
dc Input
+
Cylinder
Heil oscillator
Electron
beam
Anode 2
RF output
Heisenberg uncertainty principle See UNCER-
TAINTY PRINCIPLE.
hekto- See HECTO-.
heliacal cycle See SUNSPOT CYCLE.
helical antenna A spring-shaped antenna mounted
perpendicular to a flat metal-plate reflector, an arrangement
that produces circularly polarized
waves in a narrow beam. It is used primarily at
ultra-high and microwave radio frequencies.