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The Key to Video Cable PerformancePosted by:Steve Lampenon A pri l 05, 2012

Virtually all TV broadcasters in the USA have gone digital. Even Hollywood

has converted from film to digital images. While some of these cameras

record the data on hard drives or SSD (solid-state memory chips), at some

point you're going to send this data, those digital images, from Point A to Point

B. If you want to carry the hard drive or SSD from place to place, that's fine(so-called "sneaker net") but it is time-consuming and inefficient. Why not put

that signal on a cable to move it from place to place? That's what most

broadcasters do. And, while you could do this on fiber, converting from

electrons to photons and back again at the other end, the economical and

simple way is still over copper cable, most commonly coax cable.

The photo to the right is Belden 1694A, the world's most popular video cable.

It's a good compromise between size, distance, and cost. It is easy to put on

connectors, especially the one-piece compression connectors that Belden

now offers. (Our current record is two connectors in 33 seconds.) And these connectors, and the 1694A cable,

can carry virtually any video signal you might wish to use including analog, 4x3 digital (SD-SDI), high definition

(HD-SDI) and even 3gig (1080p/50 or 1080p/60). The only thing you have to consider is how far the cable can go.

Here's a chart showing the recommended distance for 1694A and all of our other digital cables.

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The serial digital interconnect standards are designed to operate where the signal loss at 1/2 the clock frequency

does not exceed the approximate loss value listed below.

The maximum length values shown are based on typical attenuation values for the cables listed and the following

criteria:

Maximum length = 30 dB loss at 1/2 the clock frequency: SMTPE 259M, PAL, Widescreen

Maximum length = 20 dB loss at 1/2 the clock frequency: SMTPE 292M and SMPTE 424M

The bit error rate (BER) can vary dramatically as the calculated distances are approached. BER is dependent onreceiver design and the losses of the actual coax used.

Note that 1694A shows a distance of 250 ft. at 3G (1080p/60). Some designers and installers say that is not far

enough. Well, the numbers in that table are generated by a formula that is in theSMPTEdigital standards

(SMPTE 292M, 424M etc.). These are not measured distances. A good cable, when driven by good chips, can go

much farther. For instance, we have shown at many tradeshows, a Grass Valley 'Trinix' video router, running a

3G (1080p/60) signal 544 ft. on Belden 1694A, a lot farther than 250 ft.

We just suggest that, if you pass that 250 ft. distance, you test the cable to assure performance. Bit errors, eye

patterns, anything that shows you that the signal is working. The ultimate way to test any cable (or anything else

in the line: cable, connectors, patch cords, patch panels, adaptors, bulkheads, feedthroughs etc.) is to test for

Return Loss. We do it in the lab all the time. We do it in the factory on every foot of digital cable that we make.

The graph below shows the Return Loss of our one-piece compression HD connectors. The blue line above it is

the guaranteed maximum of our digital cables. These all go out to 4.5 GHz to cover 3gig 1080p/60 applications. In

the next blog, we'll go into Impedance and Return Loss in detail.

The data above represents the typical performance you can expect from the Belden line of HD Brilliance BNC

Connectors. Again, this is not the maximum reading of a single connector, but rather the combined average of

over sixty repeat tests.

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