Appendix B • Reference and Glossary
Extron • User’s Manual • RGB 320 Switching Interface System
Distribution amplifier –
DA. A device that allows connection of one input source to multiple, isolated
(buffered) output sources such as monitors or projectors.
FCC –
Federal Communications Commission. The US governmental agency that
controls and makes all policy for the use of broadcast airwaves.
Field –
One half of a standard television frame, containing every other line of information.
Each standard video frame contains two interlaced fields, sometimes referred to
as “field 1 and field 2”.
Flicker –
An alternating change of light intensity, typically perceived at a rate of a few hertz
to 60 Hz when viewing static images such as text. Flicker can occur when the
electron gun paints the screen too slowly, giving the phosphors on the screen
time to fade before they are refreshed.
Frame –
One complete picture in interlaced video. A video frame is made up of two fields,
or two sets of interlaced lines.
Frequency range –
The low-to-high limits of a device such as a computer, projector or monitor. See
bandwidth.
Gain –
A general term used to denote an increase in signal power or voltage produced
by an amplifier. The amount of gain is usually expressed in decibels above a
reference level. Opposite of
attenuation.
Hertz –
Hz. The international term for cycles per second.
High impedance
Hi Z or High Z. In video, when the signal is not terminated it is said to have a Hi Z
load. Hi Z is typically 800-10k ohms or greater.
Horizontal rate –
Horizontal frequency. The number of complete horizontal lines (trace and retrace)
scanned per second. Typically measured in kHz.
Horizontal resolution –
The number of vertical lines that can be perceived in a video device.
Hue –
Tint control. The parameter of color that allows us to distinguish between colors.
Impedance –
Z. The opposition or “load” to a signal, measured in ohms and abbreviated
W
or
Z. In video, typical low impedance circuits (low Z) are 600 ohms or less, and high
impedance circuits (high Z) may be 10k ohms or greater. Video termination
impedance is 75 ohm. Also see
high impedance and low impedance.
Interlaced –
The process of scanning the picture onto a video screen whereby the lines of one
scanned field fall evenly between the lines of the preceding field.
IRE scale –
An oscilloscope scale that applies to composite video levels. Typically there are
140 IRE units in one volt (1 IRE = 7.14 mV).
K –
kilo. An abbreviation for 1,000. A kilobyte is 1,000 bytes. Because numbers used
in computer RAM sizes are in binary, the closest number is used. When talking
about memory size, etc., the numbers are rounded off (e.g., 1k byte is really
1,024 bytes.)
kHz –
Kilohertz. One thousand cycles per second.
LED –
Light-emitting diode. A low-power, long-life light source, usually red, green or
yellow in color. Some LEDs can produce two colors.
Level control –
The level control on some interface products is similar to the contrast control on a
data monitor. It can either increase or decrease the output signal level from the
interface to a data monitor or projector. This results in more or less contrast in the
picture.
Low impedance –
The condition where the source or load is at a lower impedance than the
characteristic impedance of the cable. Low source impedance is common; low
load impedance is usually a fault condition.
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