电子工程词典8.pdf

UHF generator • ultra-low frequencies 701 UHF generator 1. An oscillating device (such as a ultimate ratio The limiting value of a ratio (i.e., the transistor, tunnel diode, Klystron, or magnetron) value approached by a ratio). used to produce radio-frequency energy at ultra- ultimate sensitivity 1. In an instrument or sys- high frequencies (UHF). 2. The equipment in tem, the maximum degree of perception of, or re- which such a device is used. 3. An ultra-high- sponse to, a quantity or condition. 2. In a graphic frequency test-signal generator. recorder, half the deadband. UHF loop A (usually single-turn) loop antenna with ultimate threshold See ULTIMATE SENSITIVITY, a toroidal radiation pattern perpendicular to the 2. loop; the antenna has a natural wavelength in the ultimate trip current For a specified set of envi- ultra-high-frequency (UHF) range. ronmental conditions, the lowest value of current UHF receiver A receiver tunable to frequencies in that will trip a circuit breaker. any band in the range 300 MHz to 3000 MHz. ultimate trip limits For a circuit breaker, the UHF television channels Television channels 14 maximum and minimum current at which the through 69, whose frequencies lie in the ultra- breaker trips and drops out. high range. ultor anode The second anode of a television pic- UHF transistor A transistor specially designed and ture tube or oscilloscope tube. fabricated for ultra-high-frequency (UHF) opera- ultor element