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Video signal extension

05 August 2011

Kashyap Khetia, manager of product marketing at KanexPro, provides an overview of video signal extension over Cat6 cable.

There are so many ways to extend video signals but, simply, it’s truly based on the how far a system installer is extending the video signals and with what type of video formats.

In commercial AV long distance transmission of video signals is possible with various kinds of extenders, also known as signal boosters or baluns. They are comprised of a transmitter and a receiver set. The connection between the two are secured using cost-effective Cat6 cables or, if you need the ultimate distance and security on what you are sending, consider going over fibre.

We will discuss Cat6 cables since they are cost-effective, easy to terminate and are found pretty much everywhere.

Type of signal
Several types of analogue and digital signals can be delivered over Cat6. Digital signals are becoming the norm these and most customers demand DVI or HDMI signals running over Cat6. Not forgetting, control signals over IR, RS-232 and uncompressed multi-channel audio that can also be passed over Cat6 cable. All these signals are transmitted actively over Cat6 and then converted to DVI/ HDMI or other respected formats at the other end.

The challenges
When extending digital video signals at long distances, it needs to be free of sparkles, bit errors and signal loss. It’s recommended that installers test their source or display components such, such as a Blu-ray players or LCD projectors, initially before they do the final install.

Since the introduction of HDMI, distance limitations have been a frustration to integrators. In response, several manufacturers have developed extenders, converters, and adapters to solve (or in some cases) avoid the issue. There are several tactics to overcome this issue:
Consider using twisted pair extenders if applicable. Use single cable connections between devices, also use good construction and quality cable for the long-runs, implement cable equalizers whenever possible and make it easy and simple by avoiding multiple connections in the digital signal path.

Audio considerations
When transmitting multi-channel audio there is quite a bit of confusion among users. Compressed audio and uncompressed audio both play a major role in distributing audio signals over Cat6 or other media. Line level audio can be carried over Cat6 wiring if extenders are used at both ends of cable to convert the typical unbalanced audio (RCA connectors) to balanced signals. HDMI extenders use multi-channel audio (up to 7.1 surround sound).

Powered or passive?
There is a significant difference when implementing passive options over powered extenders.

The most critical one is that most passive devices like wall plates, adapters and long–cables require signal equalisation and power to drive the signals. Powered extenders include active equalisers to compensate for signal loss during long haul transmission. Passive devices can only support transmission up to a certain length whereas powered extenders can run distances up to 100m or more.

Latency
Latency or delay has always been questioned when extending HD video and audio signals over Ethernet or other media like coax. A short period of delay (in milliseconds) can cause potential issues when extending AV signals over long runs. For instance lip-sync errors. This can be fixed by using a calibration DVD and making sure the hardware complies with the right HDMI specifications.

HDCP
As the digital age embraces the distribution of HDTV, movies and music, content providers are increasingly concerned about piracy and sharing copyrighted material. Various digital rights management (DRM) schemes have been developed and one of them is HDCP- (High-bandwidth Digital Content Protection) a form of digital copy protection developed by Intel Corporation to prevent copying of digital audio and video content as it travels across connections.


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