Return Loss
An idealized input or output circuit will exactly match its desired impedance
(generally 75 ohms) as a purely resistive element, with no reactive (capacitive or
inductive elements). In the real world we can only approach the ideal. So our real
inputs and outputs will have some capacitance and inductance. This will create
impedance matching errors, especially at higher frequencies. The Return Loss of
an input or output measures how much energy is returned (reflected back due to
the impedance mismatch). For digital circuits, a return loss of 15 dB is typical.
This means that the energy returned is 15 dB less than the original signal. In
analog circuits, a 40 dB figure is expected.
RGB
RGB systems carry the totality of the picture information as independent Red,
Green, and Blue signals. Television is an additive color system, where all three
components add to produce white. Because the luminance (or detail) information
is carried partially in each of the RGB channels, all three must be carried at full
bandwidth in order to faithfully reproduce an image.
ScH Phase
Used in composite systems, ScH Phase measures the relative phase between the
leading edge of sync on line 1 of field 1 and a continuous subcarrier sinewave.
Due to the arithmetic details of both PAL and NTSC, this relationship is not the
same at the beginning of each frame. In PAL, the pattern repeats ever 4 frames (8
fields) which is also known as the Bruch Blanking sequence. In NTSC, the repeat
is every 2 frames (4 fields). This creates enormous headaches in editing systems
and the system timing of analog composite facilities.
SDI
Serial Digital Interface. This term refers to inputs and outputs of devices that
support serial digital component video. This generally means standard definition
at 270 Mb/s. The use of “HD-SDI” is beginning to appear to indicate High
Definition Serial Digital video at 1.485 Gb/s.
SMPTE
The Society of Motion Picture and Television Engineers is a professional organiza-
tion which has done tremendous work in setting standards for both the film and
television industries. The term “SMPTE’” is also shorthand for one particular
component video format - luminance and color difference.
Single mode
A Single mode (or monomode) optical fiber carries an optical signal on a very
small diameter (9 micron) core surrounded with cladding. The small diameter
means that no internally reflected lightwaves will be propagated. Thus only the
original “mode” of the signal passes down the fiber. A single mode fiber used in an
optical SDI system can carry a signal for up to 20 kilometers. Single mode fibers
require particular care in their installation due to the extremely small optical
aperture that they present at splice and connection points.
See also Multi-mode.
BrightEye-13
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