Product Review (November 2004) - Gefen
HDTV HDMI/DVI CAT-5 Extender System

One of the biggest complaints from consumers installing front projectors is the cable length limitation encountered with HDMI and DVI interfaces. As HDMI begins to make its way into the consumer electronics market complimenting the already established DVI interface, the need for longer cables become necessary, especially with the increasing popularity of front projection systems. It is not uncommon to find users asking for a long DVI or HDMI cable to solve this distance problem only to find that the video interface becomes unreliable. Unfortunately, long DVI/HDMI cables compromise signal integrity and eventually fall out of the DVI specification resulting in sparkles on the screen or a complete loss of picture. To solve this problem, Gefen Incorporated has introduced several new products that extend the length of DVI/HDMI signals. Gefen offers a variety of DVI/HDMI solutions including switchers, extenders, splitters and distribution amplifiers. The new HDTV Extender is designed to extend the HDMI interface, but is completely capable of supporting DVI signals as well when used with an adapter. Futhermore, the interface is also compatible with HDCP copy protection. Our focus will be on DVI since our products currently use this interface format. However, since more products are now showing up with the HDMI interface, we decided to review the HDMI version to show that it is fully backwards compatible with current DVI products.

If you are only intersted in DVI, Gefen also sells the DVI CAT-5 Extender that has DVI connectors instead of the HDMI connectors. Our tests utilized Accell Corporation's DVI-to-HDMI adapter along with their DVI-to-HDMI cable. The HDTV Extender supports 480P, 720p, 1080i, 1080p and other resolutions up to 1920 x 1200. The single link design supports pixel rates as high as 165 megapixels per second. In addition to 720p and 1080i signals, we ran a variety of VESA compliant timing signals to our projector with no problems.

The HDTV Extender package consists of a transmitter, a receiver, an AC power supply and an HDMI cable. The two interface boxes each have an HDMI connector and a pair of RJ-45 jacks. A standard pair of CAT-5 cables are used to transfer a single link DVI signal up to 150 feet from the source. Although Gefen does recommend using shielded cable for better noise immunity when running longer distances, non-shielded cable may work just fine in many cases. The AC power adapter plugs into the transmitter and the receiver gets its power from the transmitter through one of the CAT-5 cables. The transmitter and receiver are small and identical in size, each measuring only 3.4" W x 3.25" D x 1.25" H. The package we received also included a six-foot HDMI-to-HDMI cable.

The Problem and the Solution
DVI and HDMI use Transistion Minimized Differential Signaling (TMDS) to send data over twisted pair cables. Differential signaling is an effective way of sending signals over long distances, but as distances increase, bandwidth decreases. The signal integrity is a function of the transmitter, the cable (both length and quality) and the sink or receiver used in the setup. All three play a role in the signal performance and can be measured using the "Eye-Diagram" on a high-speed storage oscilloscope. Most of the DVI transmitters chips we've seen specifiy a cable length of up to 5 meters using quality twisted pair wires. Based on our experience, DVI reliability can vary widely depending on the setup. We have been successfully using a 20 meter AudioQuest DV-1 cable in many applications, but we have encountered some problems with using a Bravo D2 DVD player. With that said, we would advise users to minimize the DVI cable length whenever possible.

The HDTV Extender design leverages from proprietary high-speed communications technology that allows high-speed data to be reliably transmitted over standard CAT-5 cables. The HDTV CAT-5 Extender is a system that can transmit a DVI/HDMI signal up to a distance of 150 feet using two CAT-5 cables. We used unshielded CAT-5 to run approximately 50 feet and didn't encounter any problems with our setup.

The installation of the HDTV Extender is simple compared to the fiber optic based system we reviewed from Gefen . We were interested in running our own inexpensive CAT-5 cables for testing the HDTV Extender. After all, the great benefit of this product is the fact that easy to find CAT-5 cables can be installed in the walls.
Our installation required 50 feet between our DVDO iScan HD processor and our Optoma H77 DLP projector. The 1000-foot spool of unshielded CAT-5 cable was a mere $65 at the local electronics store. This comes out to less that 7 cents per foot for a total of $7 for cable (not including connectors). The Gefen manual didn't say much about the cabling so we assumed that a straight-through CAT-5 cable was required. We were correct and didn't have any problems with our custom cable length. For those do-it-yourselfers who want to build their own cables, I would recommend using a simple CAT-5 cable tester to ensure that the wiring is correct. It's possible to damage the Gefen unit with improper wiring since power is sent over the CAT-5 cable link. LEDs on both the transmitter and receiver let you know that power is getting to both units.

Our setup consisted of a Samsung SIR-T165 set-top box drive connected to a DVDO iScan HD video processor. The DVI output of the iScan HD is connected to the Gefen HDTV Extender transmitter box. The receiver unit is then plugged into our Optoma H77 high-definition DLP projector. High definition content sent from the Samsung unit is passed through the iScan processor. The Samsung has the capability to provide us with a DVI signal from terrestrial high-definition broadcasts or from our FireWire™ (iLink™) connection to our D-Theater VCR. With this setup we can play our D-VHS tapes and digitally link them to the H77. The link to the projector was very reliable and provided us with a wonderful picture.

Gefen has once again solved a practical problem faced by many consumers installing a projector into their home theater system. Unreliable HDMI and DVI interfaces due to long cables have forced many users to look for alternatives. The HDTV Extender provides a reliable HDMI/DVI connection for any display located as far as 150 feet from the source with the use of inexpensive CAT-5 cabling. In addition, full HDCP copy protection is supported, making it attractive for today's new video systems. While the system costs $500, it is actually less expensive than many high-end cables that sometimes give marginal performance. The robust design ensures a good signal to the display.

- Kevin Nakano

Review System

Projector: Optoma H77 High-Definition HD2+ DLP™ Home Theater Projector
Stewart Filmscreen 100" Luxus Deluxe FireHawk Screenwall
Preamplifier/Processor: Parasound AVC-2500U THX-Ultra DTS/DD Processor
Amplification: Parasound HCA-2205AT THX-Ultra Five Channel Amplifier
Bass Management: Miller & Kreisel BMC Mini 5.1 Bass Management Controller
Front Speakers: Miller & Kreisel S-150THX (L+R) and S-150AC (Center) Speakers
Rear Speakers: Miller & Kreisel SS-250 TripoleŽ Surround Speakers
Subwoofer: Two Miller & Kreisel MX-350THX MkII THX-Ultra Push-pull Subwoofers
Room Treatments: Echo Buster panels and Bass Buster towers
Set-top Box: Samsung SIR-T165 Terrestrial Receiver
D-VHS VCR #1: Marantz MV8300 D-VHS High-Definition D-Theater VCR
D-VHS VCR #2: JVC HM-DH30000U D-VHS High-Definition D-Theater VCR
DVD/CD/SACD Player: Sony DVP-NS900V DVD/CD/SACD Player
DVD Audio/Video Player: Kenwood Sovereign DV-5900M 400-Disc DVD Changer
Audio Switcher (5.1): Zektor MAS3 5.1 Audio Switcher
HDMI/DVI Cables: Accell Corporation HDMI/DVI Adapter and Cables
A/V Cables: DirectConnect HQRGB Cables, Accell Component Cables
Video Generator: Sencore VP403 SDTV/HDTV Video Pattern Generator
Video Signal Analyzer: Sencore VSA794 NTSC Video Signal Analyzer
Color Analyzer: Sencore CP5000 Multi-Display Color Analyzer

Review - At a Glance

Gefen - HDTV HDMI/DVI CAT-5 Extender System

• Uses CAT-5 cable for DDC and control signals
• Extends any HDMI/DVI compliant device up to 150 feet from the source
• Saves space on your desktop Increases productivity
• Eliminates computer noise where you work
• Supports 480p, 720p, 1080i, 1080p and 1920 x 1200 resolution
• Supports DDWG standard for DVI compliant monitors
• Installs in minutes

Video Amplifier Bandwidth:

1.65 GHz

Input Video Signal:1.2 volts p-p
Input DDC Signal:5 volts p-p (TTL)
HDMI Connector:5 volts p-p (TTL)
Link Connector:RJ-45
Power Consumption:15 Watts (max)
Dimensions:3.4" D x 3.25" W x 1.25" H (Transmitter and Receiver)
Shipping Weight:3 lbs.

Company Information
Gefen Inc.
Customer Service
6265 Variel Ave.
Woodland Hills, CA 91367-9897
Toll Free: 800-545-6900
Phone: 818-884-6294
Fax: 818-884-3108

Source: Manufacture loan
Model Number: HDTV Entender
MSRP: $500 (as tested)

Warranty: 1 year parts and labor


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