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Technical
Glossary - U, V
| A
| B | C
| D | E
| F | G
| H | I
| J,K | L
| M | N
| O | P
| Q | R
| S | T
| U,V | W,X,Y,Z
| Spec. Char.,
Number |
Uncertainty
The degree to which a parameter or characteristic
cannot be specifically determined.
UMTS
Universal mobile telecommunications system. The
name of the third-generation mobile phone standard
promoted by ETSI for use in Europe.
U-NII
Unlicensed national information infrastructure
spectrum, 5.8-GHz.
Upconverter
(Mixer)
A mixer whose desired output signal, called the
RF signal, is the sum of the incident baseband
(sometimes called the IF) and LO signals.
Varactor
A p-n junction diode that is designed to act as
a voltage controlled capacitance when it is operated
under reverse bias
Varactor-tuned
Oscillator
(See "voltage controlled oscillator")
VCO
(See "voltage controlled oscillator")
Vector
A mathematical representation that has both magnitude
and direction.
Vector
Modulator
A modulator that modulates both amplitude and
phase.
Video
Impedance
The video impedance of a detector diode is the
low frequency impedance looking into the diode
from the video amplifier. The symbol for video
impedance is RV. It is essentially the (AC) slope
of the diode at the bias level set up by external
bias of the RF signal. This impedance is affected
by the DC current flowing in the diode. It is
normally specified at a small (i.e., 1 - 100 microamperes)
current and can range from 500 ohms to megohms.
Some ZBD's are used without bias so RV is specified
at zero bias. The video impedance can affect the
pulse fidelity of a video detector since the RC
time constant depends on RV and the bypass capacitor
of the detector circuit.
Video
The frequency spectrum that corresponds to that
of a signal to be displayed in a television or
radar system. The video bandwidth is generally
considered to extend from DC to several megahertz.
Voltage
Breakdown
(See "Breakdown Voltage")
Voltage
Controlled Oscillator
An oscillator whose frequency is a function of
an externally generated voltage control signal.
Voltage
Tuned Filter
An electronically tunable, reactive circuit intended
to pass or block portions of the electromagnetic
spectrum, controlled by an externally generated
voltage signal.
VSAT
Very small aperture terminal.
VSWR
Voltage Standing Wave Ratio; (see "Standing
Wave Ratio").
VTF
(See "voltage tuned filter")
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