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- µ-
- Measurement: SI / Metric prefix "micro-", equal to 0.0000001 units.
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- UHF
- Acronym: Ultra High Frequencies
- Communications: The frequency band between 300 MHz to 3000 MHz.
- Video: Broadcast channels 14 through 69 (inclusive).
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- UHF Loop
- Video: An on-set antenna specifically for picking up UHF channels.
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- UL
- Acronym: Underwriters Laboratories, Inc.
Standards: Underwriters Laboratories Inc. (UL)
is an independent, not-for-profit product safety testing and
certification organization. UL has tested products for public safety
for over a century. Each year more than 17 billion UL Marks are applied
to products worldwide. UL is not affiliated with (Linker) and does not
endorse the Web site. The UL mark (shown to the right) is found on the
same types of products as the CSA mark (Canada) and the CE mark (European Union).
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- Ultra-cardioid
- Ultra High Frequency: see UHF.
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- Ultrasonic
- Communications, Audio: Frequencies higher than the human ear can hear, or higher than 20,000 Hz.
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- Ultraviolet
- Weather: Electromagnetic radiation that has a wavelength shorter than visible light and longer than x-rays.
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- UMTS
- Acronym: Universal Mobile Telecommunications Services
- Telephony: The European term for 3G cellular systems based on the IMT-2000 standard.
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- Unbalanced
- Audio: A circuit that uses a single conductor and a shield for connection. Unbalanced lines are more susceptible to line noise and interference. Compare to Balanced Line.

- Electronics: A circuit with a single branch.
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- Underexposure
- Digital Video: A picture that appears too dark because not enough light got to the imaging system.
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- Underwriters Laboratories: see UL.
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- Unidirectional
- Audio: A microphone which is designed for an improved signal to noise ratio over omnidirectional microphones. Unidirectional, or directional, microphones have a either a cardioid, hyper-cardioid or ultra-cardioid polar pattern.
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- Uninterruptible Power Supply: see UPS.
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- Uniform Resource Locator: see URL.
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- Unipolar
- Electronics: A transistor in which only one of the charge carriers (either the negative or the positive) is involved in the transistor action. Junction transistors and insulated gate field-effect transistors are unipolar transistors.
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- Unit Code
- Plug 'n Power: One of two code dials on a receiver (module). There are sixteen unit codes available, 1 - 16 When the corresponding number switch on a transmitter (controller) is pressed, any modules set to the same unit code will respond.
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- United States Weather Bureau: see .USWB
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- Universal Time Coordinate: see UTC.
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- Unity Gain: see Gain, Unity.
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- Universal Mobile Telecommunications Services: see UMTS.
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- Universal Serial Bus: see USB.
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- Unsharp Masking
- Digital Video:
A process by which the apparent detail of an image is increased;
generally accomplished by the input scanner or through computer
manipulation.
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- Uplink
- Satellite: The act of sending data from an earth station up to a satellite, or data that is sent from an earth station up to a satellite.
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- Upload
- Computers: To transfer data or programs from your computer or device to another computer or device. The opposite of Download.
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- URL
- Acronym: Uniform Resource Locator
- Internet: The address of a website, that usually starts with http://.
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- UPS
- Acronym: Uninterruptible Power Supply
- Electronics, Computers: An AC device with a large, rechargeable battery, that is connected between the AC outlet and a device to switch on and provide battery power to the device in the case of a power outage.
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- Upwind
- Weather: The direction from which the wind is blowing. Also the windward side of an object. The opposite of the downwind or leeward side.
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- USB
- Acronym: Universal Serial Bus
- Computers: A high-speed port found on digital photography devices and newer computers, that allows much faster transfer speeds than a serial or parallel port.
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- USWB
- Acronym: United States Weather Bureau
- Weather: the official name of the National Weather Service prior to 1970.
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- Use (or Usage) Life
- Batteries: A rating that describes how long a particular battery will last in a particular device.
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- UTC
- Acronym: Universal Time Coordinate
- Weather:
one of several names for the twenty-four hour time which is used
throughout the scientific and military communities. Other names for
this time system are Zulu (Z) and Greenwich Mean Time (GMT)
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- UV
- Acronym: UltraViolet
- Communications, Electronics: The electromagnetic radiation band between visible light and x-rays.
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- UXGA
- Digital Video: An image resolution of 1600 x 1200 pixels.
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