TUNED CIRCUIT(1) A circuit consisting of inductance and capacitance that can be adjusted for
resonance at a desired frequency . (2) A circuit that is used as a filter which passes or rejects specific
frequecies . (3) An LC circuit used as a frequency-determining device .
TUNED LINEAnother name for the resonant line. This line uses tuning devices to eliminate the
reactance and transfer maximum power from the source to the line .
TUNNEL DIODEA heavily doped semiconductor device that has high gain and fast switching
capabilities . See NEGATIVE-RESISTANCE ELEMENT .
TUNNELINGThe piercing of a potential barrier in a semiconductor by a particle (current carrier) that
does not have sufficient energy to go over the barrier .
TURNOne complete loop of a conductor about a core .
TURNS RATIOThe ratio of the number of turns in the primary winding to the number of turns in the
secondary winding of a transformer .
TURNSTILE ANTENNAA type of antenna used in vhf communications that is omnidirectional and
consists of two horizontal half-wave antennas mounted at right angles to each other in the horizontal
TWISTED PAIRA line consisting of two insulated wires twisted together to form a flexible line without
the use of spacers .
TWO-DIMENSIONAL RADAR (2D)Measures the range and bearing to a target .
TWO-M (2M)Miniature/microminiature repair program .
TWO-WIRE OPEN LINEA parallel line consisting of two wires that are generally spaced from 2 to 6
inches apart by insulating spacers .
TWO-WIRE RIBBON (TWIN LEAD)A parallel two-wire line in which uniform spacing is assured by
two wires imbedded in a low-loss dielectric .
ULTRAHIGH FREQUENCYThe band of frequencies from 300 megahertz to 3 gigahertz .
ULTRASONIC(1) Sounds above 20,000 hertz . (2) Supersonic.
UNBALANCED CRYSTAL MIXERA circuit consisting of a section of coaxial transmission line
one-half wavelength long that is tuned to the difference (intermediate) frequency between the local
oscillator and RF echo signals .
UNIDIRECTIONALIn one direction only .
UNIDIRECTIONAL ARRAYAn antenna array that radiates in only one general direction .
UNIJUNCTION TRANSISTOR (UJT)A three-terminal, semiconductor device with a negative
resistance characteristic that is used in switching circuits, oscillators, and wave-shaping circuits .
UNIT(1) An assembly or any combination of parts, subassemblies, and assemblies mounted together.
Normally capable of independent operation . (2) A single object or thing .
UNIT SIZEThe standards adopted to make comparisons between things of like value (for example, the
unit size for conductors is the mil-foot) .