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BLACK BOX
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Education | Distribution Methods
Cable-Based Distribution
Remote
Display
In-Line
Extender
DVI Cable
DVI Cable
DVD Player
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Fiber Optic Cable
Audio Cable
DVI Cables
DVI
Cables
Local Monitor
Remote
Displays
Laptop
Fiber-Based DVI
Extender Transmitter
and Receiver
In-line based
In-line extenders, installed at some point within a link, extend signals over
their native cabling with no signal conversion occurring. These
amplification or repeater types of devices are designed to equalize and
amplify the signal to go greater distances. Some support daisychaining, so
by stringing two of them together you can send data double the distance.
But in-line extenders can only take the signal so far and typically use
amplification that not only boosts the video signal, but also boosts any
noise on the cable. In addition, they don’t solve the problem of having to
transmit bidirectional serial control signals to the display.
Non-networked CATx-based
This method uses transmitters and receivers to extend converted signals
over non-networked UTP cabling. They’re very cost-effective, enabling
much longer distances than what’s ordinarily possible with analog or
digital video cabling.
Copper-based extension is also a great alternative to using standard video
or RGB coax cables, which often can’t be easily pulled through tight
conduits and can be more difficult to terminate (for more on the
limitations of simply extending video cabling, see below).
A bonus: In most buildings, copper cabling is already installed to service
data communications. There’s no need to pull new cabling when existing
wiring can be used for long-distance AV distribution instead.
Another thing to consider: Coax- or VGA-cabled extension installations
usually require a separate RS-232 or other line for transmitting the control
signal for a display—yet another cable to fit into the conduit and another
distance limitation (most serial signals can travel only a short distance over
traditional cable). Some CATx-based extenders also extend serial control
signals in addition to video and audio. Therefore the cable can deliver
both the video and control signals through a single transmission medium.
Plus, CATx extension technology continues to evolve. Newer HDBaseT
™
technology uses sophisticated encoding and equalization techniques to
deliver uncompressed DVI or HDMI video and audio, 100BASE-T Ethernet,
power, and control signals to a remote screen—all over a single CATx
cable. HDBaseT has made it possible to transmit the video signal as well as
the peripheral signals uncompressed up to 100 m.
Why not just run longer cables?
An analog video signal can be run over long lengths of native VGA cable
as long as its diameter and shielding is good enough. However, regardless
of the cable quality, signal attenuation increases with video frequency and
cable length. This means that after 30 to 50 feet, the image quality will
start to degrade. This leads to color skew and smeared-looking text.
To solve for signal degradation in VGA video applications, use an equalizer,
or an extender that compensates for signal loss. A good extender has
separate adjustments for high and low frequencies; HF loss is usually
greater than LF loss.
Analog signals travel in a sine-like wave form; digital DVI and HDMI signals
travel in a square-like waveform. The signal is broken into a binary format
where the audio or video data is represented by a series of 1s and 0s. Like
analog signals, digital video also suffers from cable loss, but as long as the
cable is of sufficient quality and within the maximum supported distance,
the signals don’t suffer blurring or color skew.
So what happens when the maximum supported length is exceeded? You
get the “cliff” effect, where the signal drops off and you completely lose
the picture. To overcome distance limitations, use extenders or repeaters.
Non-networked fiber-based
Using fiber-based technology has many advantages over copper-based
distribution technology. Foremost, it enables you to deliver video at much
longer distances than copper—without compromising the quality of the
original video signal. This makes it an ideal distribution method for digital
signage.
Plus, it supports high resolutions and the sending of large, bandwidth-
consuming files, particularly in electronically noisy environments, such
as in transit stations. Because fiber is made of glass, which is an insulator,
no electric current can flow through. This makes it immune to EMI/RFI
interference. You can run fiber next to industrial equipment without
worry. And, compared with copper cable, fiber cable is less susceptible
to temperature fluctuations.
In addition, fiber distribution is ideal for applications where data security
is a priority, such as in medical, military, and government environments.
That’s because fiber cable is extremely difficult to tap.
And fiber cable is more durable than copper cable, and it’s thinner. Its size
makes it easier to handle, and it takes up less space in cabling ducts. Yes,
fiber is more expensive, but many fiber-based extenders use just a single
strand of fiber, for a more economical use of your fiber count.
CATx Cable
HDMI Cable
HDMI Cable
CATx-Based Extender Transmitter and Receiver
Blu-ray Player
Remote
Display