422 Chapter 14
time on the component parts. For instance, all Belden
bundled coax cables are guaranteed to be 5 ns (nano-
second) difference per 100 ft of cable. Other manufac-
turers should have a similar specification and/or
guarantee. The de facto timing requirement for broad-
cast RGB is a maximum of 40 ns. Timing cables by
hand with a vectorscope allows the installer to achieve
timing errors of >1 ns. Bundled cables made for digital
video can also be used for RGB analog, and similar
signals (Y, R–Y, B–Y or Y, Pb, Pr or YUV or VGA,
SVGA, XGA, etc.) although the timing requirements for
VGA and that family of signals has not been established.
These bundled coaxes come in other version besides
just three coax RGB. Often the horizontal and vertical
synchronizing signals (H and V) are carried with the
green video signal on the green coax. For even greater
control, these signals can be carried by a single coax
(often called RGBS) or five coaxes, one for each signal
(called RGBHV). These cables are becoming more
common in the home, where they are often referred to as
five-wire video. There are also four-pair UTP data
cables made especially to run RGB and VGA signals.
Some of these have timing tolerance (called delay skew
in the UTP world) that is seriously superior to bundled
coaxes. However, the video signals would have to be
converted from 75:to 100: , and the baluns to do this,
one for each end of the cable, would be added to the cost
of the installation. Further, the impedance tolerance of
coax, even poorly made coax, is dramatically superior to
twisted pairs. Even bonded twisted pairs are, at best,
±7: , where most coaxial cables are ±3: , with preci-
sion cables being twice as good as that, or even better.
14.10.9 VGA and Family
VGA stands for video graphics array. It is an analog for-
mat to connect progressive video source to displays,
such as projectors and screens. VGA comes in a number
of formats, based on resolution. These are shown in
Table 14-24.
There are many more variations in resolution and
bandwidth than the ones shown in Table 14-24.
14.11 Digital Video
There are many formats for digital video, for both con-
sumer, commercial and professional applications. This
section concentrates on the professional applications,
mainly SD-SDI (standard definition—serial digital inter-
face) and HD-SDI (high-definition—serial digital inter-
face.) There are sections on related consumer standards
such as DVI (Section 14.9.4.1) and HDMI (Section
14.9.4.2).14.11.1 Digital Signals and Digital CableControl communications, or data communications, uses
digital signals. Digital video signals require wide band-
width cabling. Control communications and data com-
munications use lower-performance cabling because
they carry less information, requiring less bandwidth.
High-speed data communications systems have signifi-
cant overhead added to handle error correction so if data
is lost, it can be re-sent. Digital video has some error
correction capabilities, however, if all of the data bits
required to make the system work are not received, pic-
ture quality is reduced or lost completely. Table 14-25
compares various digital formats.14.11.2 Coax and SDIMost professional broadcast formats (SDI and HD-SDI)
are in a serial format and use a single coaxial cable with
BNC connectors. Emerging higher resolution formats,
such as 1080p/60, are also BNC based. Some work with
smaller connectors for dense applications, such as patch
panels and routers, which use subminiature connectors
such as LCC, DIN 1.0/2.3 or DIN 1.0/2.5. Proprietary
miniature BNC connectors are also available.14.11.3 Cables and SDIThe most common form of SDI, component SDI, oper-
ates at data rates of 270 Mbps (clock 135 MHz). Cable
loss specifications for standard SDI are specified in
SMPTE 259M and ITUR BT.601. The maximum cable
length is specified as 30 dB signal loss at one-half theTable 14-24. Resolution of Various VGA and Family
Formats
Signal Type ResolutionVGA 640 × 480
SVGA 800 × 600
XGA 1024 × 768
WXGA 1280 × 720
SXGA 1280 × 1024
SXGA-HD 1600 × 1200
WSXGA 1680 × 1050
QXGA 2048 × 1536
QUSXG 3840 × 2400