Electronics (Mike Jaroch)


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U

ULTRAHIGH FREQUENCY

The band of frequencies from 300 megahertz to 3 gigahertz [17].

ULTRASONIC

(1) Sounds above 20,000 hertz [10]. (2) Supersonic.

UNBALANCED CRYSTAL MIXER

A 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 [18].


UNIDIRECTIONAL

In one direction only [1].

UNIDIRECTIONAL ARRAY

An antenna array that radiates in only one general direction [10].

UNIJUNCTION TRANSISTOR

(UJT)—A three-terminal, semiconductor device with a negative resistance characteristic that is used in switching circuits, oscillators, and wave-shaping circuits [7]


UNIT

(1) An assembly or any combination of parts, subassemblies, and assemblies mounted together. Normally capable of independent operation [17]. (2) A single object or thing [13].


UNIT SIZE

The standards adopted to make comparisons between things of like value (for example, the unit size for conductors is the mil-foot) [4].


UNIVERSAL TIME CONSTANT CHART

A chart used to find the time constant of a circuit if the impressed voltage and the values of R and C or R and L are known [2].


UNTUNED LINE

Another name for the flat or nonresonant line [10].

UP LINK

The frequency used to transmit a signal from earth to a satellite [17].

UPPER SIDEBAND

All of the sum frequencies above the carrier [12].

UPPER-FREQUENCY CUTOFF

The highest frequency a circuit can pass [9].


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