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How to estimate 12Gbit/s SDI cable performance

16 Nov 2015  | Don Schelle

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Normalizing and tabulating cable loss at specific frequencies (table) reveals that not all cables perform equally.


Table: Cable loss at specific frequencies.


Plotting attenuation across cable length (figure 2) enables a quick comparison of how a given cable equaliser will perform with various cables. In this example, a cable equaliser capable of compensating for 38 dB of loss at 12Gbit/s will deliver approximately 65 m of cable reach using Belden 1694A. A boutique cable such as the Canare L-8CHD yields almost twice the reach: 120 m.


Figure 2: Plotting loss across cable length at a given data rate enables easy comparison between cable types.


While there is no substitute for bench testing, the calculations performed here are a good starting point to obtain approximate comparative reach across numerous cable types with a given cable equaliser. Note that the calculations presented here represent loss caused by the cable only. Losses due to the BNC connectors & PCBs, and crosstalk or other interference, are not factored in. While it's possible to make a comparative analysis, a direct quantitative analysis will show some error due to these additional sources of loss.

Most – but not all – manufacturers specify cable reach with a given cable type. In the absence of a specification, the only way to be sure is to ask.


References
Donald Schelle and Mark Brouwer. "Digitize graphical data easily and accurately" EDN, March 25, 2013.


About the author
Donald Schelle is an analogue field applications engineer for Texas Instruments and has more than a decade of engineering experience. He received his bachelor's degree in electrical engineering from Lakehead University in Thunder Bay, Ontario, Canada.


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