Peer Review: Gefen DVI CAT-5 Extender
Peer Review: Gefen DVI CAT-5 Extender, Price $499
Product: Gefen DVI CAT-5 Extender
Company website: www.gefen.com
Plus: Compact; powered at transmitter; maintains pristine image quality
Minus: Requires two Cat5 cables
THE ADVENT of digital connectors on displays, projectors, CPUs, and DVD players has enabled integrators to make connections between these devices without converting the signal to analog and then back to digital. This multiple-signal process occurs when a CPU is connected to a plasma, LCD, or projector. The digital content is converted to an analog connector (VGA or HD-15 connector) and then connected to a similar analog connector on the display device, which then converts the information back into a digital signal for display. This process ultimately lowers the quality of the signal, even if it's only traveling 6 to 10 feet.
To address this problem, plasma, LCD, and projector manufacturers have integrated DVI and newer HDMI digital connectors into their display devices to preserve the stunning image quality that results from a direct digital connection. This enhanced image quality is apparent even on older plasmas that lack acceptable analog-to-digital converters (ADCs), because the digital content is never converted to analog.
However, the distance limitations of DVI and HDMI have largely outweighed the benefits of direct digital connections. Because the distance from CPU to display device in a typical boardroom or classroom often exceeds the recommended distances for DVI and HDMI cabling, DVI use has been slow to catch on and HDMI appears to be on a similar path in the pro AV space.
Fortunately, Gefen has released a product that addresses the mid-range distance limitations for DVI and HDMI. Part of Gefen's Extender line, the DVI CAT-5 Extender uses Cat5 cabling to extend the range of digital or analog signals and can transmit a DVI signal over a distance of 100 feet without signal degradation.Design
The DVI CAT-5 Extender consists of two units: a transmitter and a receiver, each measuring approximately 3.5 inches square and 1.25 inches high. The receiver includes two RJ45 connectors and a standard DVI connector, while the transmitter has a power connector, two RJ45 connectors, and an HDMI connector (HDMI connectors are smaller than a DVI connector but carry the same video signal as a DVI connector). The units also come with a power supply and the appropriate DVI and DVI-to-HDMI cables.
While the DVI video signal is sent across one Cat5 cable, the second RJ45 connector on the transmitter and receiver carries the digital control signal and power. The transmitter powers the receiver, which allows the receiver to be placed in close proximity to the display device without the need for additional power. The use of two cables also lessens the possibility that the critical digital control signal will be lost or distorted over a longer signal run; the control signal is used to alert the CPUs to the display's optimal resolution and is necessary for proper DVI display.Performance
The system's setup is straightforward. I tested the DVI CAT-5 Extender on two CPUs: an Apple PowerBook in widescreen mode (1280x854) and a Dell Dimension desktop in standard 4:3 mode (1024x768). To verify all display of both CPUs, I first connected each CPU directly to a DVI-capable display device (a Dell 30-inch LCD TV) via a 6-foot DVI cable. I then connected each CPU to the DVI CAT-5 transmitter via the DVI-to-HDMI cable, and connected the Dell 30-inch LCD TV to the receiver. Image quality with the DVI CAT-5 Extender was visibly identical to the image quality of the 6-foot DVI cable, even when tested to 50 feet (the maximum length I tested). One setup recommendation is to connect the Cat5 cables and display prior to connecting the CPU or other playback device because most CPUs will automatically re-adjust display settings when a DVI display device is connected.
Because the signals are transmitted digitally across the dual Cat5 cables, I also found that the two Cat5 cables didn't need to be the same length. This eliminates an issue that has plagued analog VGA-over-Cat5 transmission systems, which require skew control for mismatched conductor lengths on an eight-conductor Cat5 or 5e cable, and offers integrators more flexibility if cable routing becomes an issue.Value
With a street price of less than $500 (ordered directly from Gefen), the DVI CAT-5 Extender is an excellent value. The only other feature I'd prefer on the HDMI version is the ability to carry audio along with the video, which HDMI is designed to do. I'd highly recommend the Gefen DVI CAT-5 Extender for applications such as large classrooms or locations requiring very high-resolution data display where it's not possible to mount the signal source within 10 feet of the projector, plasma, or LCD display.
Based on DVI's pristine signal quality resulting from the elimination of the digital-to-analog-to-digital conversion process, and given the prevalence of DVI and HDMI connectors on current display devices, this product fits a niche that hasn't been adequately addressed until now.
Tim Siglin is an industry analyst and co-founder of Transitions Inc., a business and technology development firm serving startups and Fortune 10 clients in the United States, Europe, and the Pacific Rim. He can be reached at firstname.lastname@example.org