Tektronix 1740A Series, User Manual

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Glossary
1740A/1750A/1760 – Series Service Manual
Glossary–3
dB (Decibel) A decibel is a logarithmic unit used to describe signal ratios. For
voltages, dB = 20 Log
10
(V
1
/V
2
).
DC-Coupled
A connection configured so that both the signal (ac component)
and the constant voltage on which it is riding (dc component) are passed through.
DC Restorer
A circuit used in picture monitors and waveform monitors to
clamp one point of the waveform to a fixed dc level.
Demodulator In general, this term refers to any device which recovers the
original signal after it has modulated a high-frequency carrier. In television it
may refer to:
(1) An instrument, such as a TEKTRONIX 1450, which takes video in its
transmitted form (modulated onto the picture carrier) and converts it to baseband.
(2) The circuits which recover R–Y and B–Y for NTSC systems or U and V for
PAL systems from the composite signal.
Diamond Diamond display. A simplified vector display for RGB signals that
defines the valid gamut limits in the form of two diamonds.
Distortion
If a sine wave of a single frequency is put into a system, and
harmonic content at multiples of that frequency appears at the output, there is
harmonic distortion present in the system. Harmonic distortion is caused by
nonlinearities in the system.
Equalizer
The pulses which occur before and after the broad pulses in the
vertical interval.
Envelope Detection A demodulation process in which the shape of the RF
envelope is sensed. This is the process used by a diode detector.
Field
In interlaced scan systems, the information for one picture is divided up
into two fields. Each field contains one half of the lines required to produce the
entire picture. Adjacent lines in the picture are in alternate fields.
Frequency Modulation (FM) is the process by which the frequency of a
carrier signal is varied in proportion to the signal of interest. In both the NTSC
and PAL television systems, audio information is transmitted using FM.
Frame A frame (sometimes called a “picture”) contains all the information
required for a complete picture. For interlaced scan systems, there are two fields
in a frame.
Front Porch
The portion of the video signal between the end of active picture
time and the leading edge of horizontal sync.
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