DVI 1000HD DVI Extender System
DVI
has become the interface of choice for today's videophiles and home theater
enthusiasts. Many higher end video products now come standard with this
digital interface, which increases the demand for DVI cables. While plasmas
and RPTVs usually don't run into cable length issues, ceiling mounted
projectors located far from the main video source often need cables longer
than those currently available. Sending this very high-speed data requires
a robust interface and increasing the cable length usually results in
degraded signal integrity. Due to the encoding process that serializes
the RGB video, a single DVI link requires data rates around ten times
the actual pixel rate. The DVI interface uses four TMDS (Transition Minimized
Differential Signaling) channels developed by the folks at Silicon Image
with serial data rates often exceeding 1 GHz (one billion bits per second)
as resolutions and scan rates increase. For this reason manufacturers
are reluctant to produce long DVI cables that would inevitably reduce
the noise margin to a point where data may become unreliable. Sending
digital data to the display or projector using DVI has some significant
advantages over standard analog RGB or YPrPb cables. Long cable runs increase
capacitance and usually result in some loss of high frequency detail giving
the picture a softer look. In addition, slight impedance mismatches in
the cable can result in ringing and other anomalies that are objectionable
on large screen displays.
Gefen Incorporated, a manufacturer of DVI products, appears to have solved this problem by converting electrical data into high-speed fiber optic data. The design uses two dual mode LC fiber optic cables for a total of four fibers. This allows each of the four TMDS channels defined in the DVI specification to have its own fiber optic link. Using the DVI 1000HDS and DVI 1000HDR units, data can be transmitted and received over very long distances without the concern of signal degradation. The DVI 1000 is designed to work with data rates as high as 1920x1200. The design supports the DDWG (Digital Display Working Group) specification for DVI compliant monitors. The chassis design for the sender and receiver are identical in size, measuring only 3.25" D x 4.25" W x 1" H.
Fibers
The four fiber optic cables used in the system are bundled into a single
jacket, making it easier to handle and less likely to damage. However,
I would caution those who use this system to take special care not to
kink or stress the cable in any way. Doing so may indeed break a fiber
and render the system useless until the fiber is replaced. I'm currently
working on a project where we use fiber optic cables and we have broken
them in some instances, so I tend to lean towards the cautious side. Rubber
plugs are placed into the optical jacks located on the sender and receiver
units to prevent contamination from entering the openings. Likewise, caps
are installed on the fiber cable ends to keep them clean.
The DVI 1000HD system is designed to run distances as long as 500 meters or 1640 feet. That's well over a 1/4 mile in length. The interface also requires a CAT5 cable the same length as the fiber cables, but runs at a much slower data rate. The CAT5 is used to send HDCP/DDC and control signals. Yes, this system is fully HDCP compliant, so you can rest assured that encrypted data will make it to your display. This is especially important as we move into an era of strict content protection from studios and broadcasters.
Installation
Installation is very simple with the fiber optic and CAT5 cable connectors
clicking into place on each of the units. The most difficult task is routing
the cables in the walls and through the ceiling. Both the transmitter
and receiver have DVI and power connectors. We connected the supplied
6-foot DVI cable to our Marantz VP-12S2 projector and Gefen receiver unit.
We used an Accell Corporation Gold Series DVI cable between the Mitsubishi
HD-5000 set-top receiver and
the Gefen transmitter unit. Powering the DVI 1000HD requires that only
one of the two units be plugged into the power adapter. The user can choose
whatever side is more convenient to power without any difference in video
performance. The unpowered unit gets its power from the CAT5 interface
cable. We installed the power adapter on the transmitter since we had
sufficient room near our Marantz VP-12S2 projector. Once the link is made
and power is applied to the system, the
Power and Status
indicators on the front of the units let you know everything is working
correctly.
Performance
We watched several different television programs using the new Mitsubishi
HD-5000 set-top receiver with a Marantz VP-12S2 projector and Mitsubishi
PD-5010 plasma display. Here in Los Angeles, the Tonight
Show offers an excellent picture and was one of the first high-definition
programs to air in the area. The DVI1000HD system worked very well and
produced an excellent picture over the 100 feet of cable with no problem
at all. We also watched an episode of Law
& Order: Special Victims Unit on KNBC and the picture was
equally impressive. This setup appeared to be working flawlessly in our
setup with absolutely no dropouts or anomalies that would degrade the
video performance. As a comparison, we swapped out the DVI 1000HD system
with a 30-foot Transparent High Performance DVI cable and saw no difference
in video quality between the two setups. The Transparent cable we used
in the comparison retails for about $1000 and has excellent performance.
The cost for the Gefen DVI 1000HD system with 100 feet of fiber optic
cable costs $1,378 (as tested) and performed equally as well with our
DVI/HDCP products. The obvious advantage of the Gefen DVI 1000HD is that
it can run very long distances while maintaining DVI signal integrity.
Conclusion
Videophiles typically choose specific cables for specific video applications.
The high bandwidth requirements of HDTV and especially DVI, forces consumers
to pay more attention to this issue. As a result, spending more money
on quality cables can be rationalized to many consumers building their
home theater system. DVI interfaces have certainly become more common
and the vast majority of us can get away with short simple cables for
our display. However, if distance becomes a barrier for large theater
rooms, Gefen's DVI 1000HD system offers a real solution without the worry
of degrading the picture over the long cables runs. Since HDCP equipment
is also becoming a reality, this must be addressed and fortunately the
DVI 1000HD is fully compliant. I'm currently not aware of any other company
making this type of system for the home theater market. While the cost
of the interface may seem high, just compare it to any of the long cables
being offered by the high-end manufacturers. Few companies are capable
of producing long cables that work reliably (50+ feet) and none have lengths
(1/4+ mile) that even come close to the Gefen DVI 1000HD system.
- Kevin Nakano
