Progress to progressive

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Steve Lampen, multimedia technology manager of Belden sheds light on what's next after HD-SDI.

There's a famous quote from Charles H. Duell, who, in 1899 was Patents Commissioner in the United States.

He said, "Everything that can be invented has been invented!"

Of course, we laugh at that now, because our entire technological world has appeared since then. And it doesn't look like our technological rush will be slowing down any time soon!

When it comes to video for instance, don't think for a minute that HD-SDI is the ‘end of the line'.

Next up is 1080p/50, a format with even higher resolution. ‘Regular' HD-SDI (720p or 1080i) has a bandwidth of 1.5 Gigabits-per-second (Gbps), and a clock of half that number (750 MHz).

Since we are working with data here, and data is square waves (or is supposed to be square waves), we know that a perfect square wave is a fundamental (clock) frequency with an infinite number of harmonics added in.

Since it is impossible to make cable, or anything else, that can handle infinite harmonics, we must instead choose how many harmonics to check.

The rule of thumb has always been to check video data streams to the third harmonic.

That would mean a standard HD-SDI signal (750 MHz clock) should be tested to the third harmonic (750 MHz x 3 = 2.25 GHz).

This simply means that anything intended to carry HD-SDI should be tested to 2.25 GHz. This would include cable, connectors, patch cords, patch panels and pretty much anything.

The only things that you don't have to worry about are those items that are less than a quarter of a wavelength at 2.25 GHz.

The wavelength of 2.25 GHz is slightly more than 5.25" so a quarter-wavelength is slightly more than 1.3 inches. What's that small? Maybe one connector.

This means that you could have one connector that is bad, or installed wrong, and everything would still work. But that's about it. Two connectors would be over that distance, and everything else, patch cords, patch cable, and certainly the cable in the run itself, has to be as close to 75 ohms as possible.

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