HDMI Retractable Cable Considerations

Introduction

A few months ago Altinex introduced the RT300-125 HDMI cable retractor for use in Audio Visual applications. This retractor utilizes a special high strength flat cable to achieve small size and high performance.

 

All HDMI retractors have been tested to 10,000 retract cycles before release to production. In addition, a special dampener is installed in every retractor to ensure a smooth and controlled cable retract. The RT300-125 retractor also has a built-in active signal equalizer to maintain HDMI signal quality on the cable output. The cable equalizer is designed to compensate for a thin cable design.

 

Whenever you work with HDMI signals, special consideration must be given to the total cable length from a source to a display. In many cases excessive cable length will create intermittent performance.

 

Discussion

Recently I received a call from my customer complaining about signal loss from the RT300-125 HDMI retractor.

Blog 12102015 - Figure 1 - Ultra compact HDMI retractor RT300-125

Figure 1: Ultra compact HDMI retractor RT300-125

 

In a short discussion we determined that the retractor was not the only cable in the signal path. In addition to the retractor, the customer had added an HDMI gender changer and a 25 ft. HDMI extension cable, which seems to be a logical thing to do.

 

Unfortunately, this system configuration is a bit dicey for a robust HDMI signal transmission.

 

Blog 01252016 - Figure 2 - HDMI signal path from a source to display

Figure 2: HDMI signal path from a source to a display


I already knew that inserting a gender changer and adding a 25 ft. cable was a recipe for intermittent connections and a possible complete signal failure at higher resolutions. What he needed was a good HDMI repeater with external power supply. Many HDMI repeaters are designed to take power from an HDMI source. With power consumption in 50-200 mA, that would drain portable devices very quickly. In general I recommend only HDMI repeaters that are powered by an external power supply.

 

Further discussion revealed that the installer was scheduled to fly home the same day and there were no plans to stay another night at the customer site. There was no time to ship anything at this point. Considering limited options, I searched the good old trusty Radio Shack website. Sure enough, there was one near the customer’s facility and they had the HDMI repeater that would do the trick.

 

Blog 01252015 - Figure 3 - Radio Shack #1500540 HDMI repeater

Figure 3: Radio Shack #1500540 HDMI Repeater


The repeater’s function is to recover and regenerate the signal to the original HDMI level for reliable system operation.

 

Blog 01252016 - Figure 4 - System configuration with HDMI repeater installed

Figure 4: System configuration with HDMI repeater installed


Depending on your application the HDMI repeater can be installed at the end of the cable closer to the display, but that would require an additional HDMI cable to connect to a display.

Conclusion

Extending HDMI signal beyond 20 ft. using a standard HDMI cable is possible, yet in some cases combination of cables and gender changers can introduce signal attenuation that will make images flicker and, sometimes, disappear completely. Using a good quality HDMI repeater will resolve these issues. When I go out to visit customers, an HDMI repeater is always in my toolbox.

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