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BJC Bonded-Pair HDMI Cables--Specs and Details

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The History, Technology, and Reasoning behind bonded-pair HDMI cable:

When we entered the cable business, HDMI was not much more than a twinkle in the consumer electronics industry's eye and a spec document; in the last few years, however, HDMI has become an increasingly common, and important, signal format for consumer electronics, and as it has become more common, more and more problems with its implementation have appeared. The signal is fragile, and while it's very reliable over short distances, it can be hard to send HDMI signals down long cables because the inherent impedance stability problems in twisted-pair cabling tend to limit distance.

Without getting too far into the technical details, the main issues presented by conventional HDMI cable design are (1) return loss, which increases dramatically with frequency and causes bit edges in a digital signal to round off and become harder to detect, and (2) interpair and intrapair skew, or timing error, which causes signals in each of the four data pairs in an HDMI cable to arrive at a somewhat different time from the others. The longer a cable is, and the higher the bitrate of the signal is, the more trouble one will typically have with return loss and skew; and as bit edges get rounded, and the transition points become harder to identify and synchronize with one another, the signal becomes harder to reconstitute. Up to a point, this won't matter; but once one crosses the threshold to partial failure, total failure is not far behind. What begins with a few "sparkly" bit-error dropouts on the screen can, with a few more feet of cable, a less-tolerant display, or a higher-resolution signal, rapidly turn into an unwatchable signal, or no signal at all. And this is a real problem, because the makers of consumer electronic devices keep shoving more and more data through the HDMI port. Yesterday, 1080i was as high a resolution as anyone needed to support; today, 1080p, at double the required bandwidth, is increasingly common; and tomorrow, "deep color," at 12 or 16 bits rather than the current eight bits, may become the standard, increasing the bandwidth again. Cables that worked yesterday will not necessarily work tomorrow.

HDMI cable sold by American vendors is sourced, in every case we know of, from one or another of a handful of cable manufacturing and assembly companies in China. Many American vendors simply put a U.S. brand on a Chinese cable and say nothing about the source; many others make claims, which are hard to verify, about their HDMI products being of proprietary design, though it's often hard to tell whether "proprietary design" refers to trivial choices like the PVC jacket color or to something more meaningful. We are a manufacturing and assembly company, and we are not content with just buying something from overseas, relabeling it, and pushing it out the door; our aim is to build the best products possible, not to be a resale company for Chinese goods. When we say that a cable we carry is our own design, we want that to mean something substantial; we want to have had true, meaningful involvement in defining the product's functional characteristics, not to have just picked it out of a catalog of options.

Apart from the technical issues, we always found it troubling that all of the HDMI cable on the market was made in China. Whether because of workers' rights issues, environmental considerations, or broader global political concerns, we don't like to be responsible for outsourcing jobs to authoritarian nations if it can be avoided; and knowing that the best cable products in the world are not made in China, but in the U.S., we thought we could do something about that. We are a small company, but we buy and sell enough HDMI cable that it seemed realistic to ask: what can we do to make an HDMI cable that is (1) better than existing products, and (2) sourced, to the maximum extent possible, from the U.S.?

We have always bought most of our cable from Belden, in Richmond, Indiana. Belden is a hundred-year-old American wire and cable manufacturer with a wide range of technical achievements to its credit, and has long been the leader in professional broadcast-quality cable products. Belden holds the patent on a technology called "bonded pairs," which is a way of making twisted-pair cable more consistent; a bonded pair, rather than consisting simply of two wires twisted together, has the wires actually stuck to one another. This allows for tighter control over critical dimensions like the wire-to-wire spacing, and it allows the cable to maintain its characteristics under flexing conditions, and the result is that the cable has better impedance consistency, lower return loss (especially at high frequencies), lower intrapair skew (because the wires within a pair are closely matched for length), and lower interpair skew (because the characteristics of different pairs within the bundle are more closely matched). Bonded pair technology had been applied to various data cable products, but never to HDMI cable, when we first approached Belden in 2005 and asked for a custom HDMI cable product to be designed.

Since our first meeting with Belden's product development staff in 2005, we have been through multiple sample reels of cable, tests, consultation and redesign, working together with Belden's engineering department to put together what we believe is the best HDMI cable in the world, one that incorporates unique technology not available in any other product. At this writing, the BJC Series-1 is the only bonded-pair HDMI cable available from anyone, anywhere in the world. It is the only HDMI cable manufactured in America by American workers. At this time, we are shipping the American-made bulk cable to China for termination, because connectors currently available on the market are labor-intensive to affix and therefore are not suitable for a high-cost labor market like the U.S., and the finished cable assemblies would be excessively-priced if we did the terminations here; but we are in the process now of prototyping a new connector design that will both facilitate efficient termination of these cables here in Seattle rather than in China and improve the physical stability of the fragile HDMI connector, and it is our goal to bring the cable termination process in-house if possible, and as soon as possible.

And how is the product? We have been stunned with the good results of all this development work. Running sample cables at a variety of lengths, in in-use testing, we've found that the cable perfectly conveys 1080p/60 video 125 feet, and 720p and 1080i 150 feet (one caveat: maximum distances are dependent upon source and display circuitry, so results may vary). The actual maximum "spec-compliant" lengths are yet to be determined, but these in-use distances are extraordinary, and have been matched, to our knowledge, only by cables incorporating amplifiers and active EQ circuits. We are proud of the distances we've been able to span with this cable, in part because active circuitry really ought to be avoided when mere wire and plastic, deployed in the right configuration and manufactured to the right tolerances, will do. Active circuitry introduces whole new ways for a system to fail; more to buy, more to troubleshoot.

There will always be less expensive HDMI cables on the market; and if your application doesn't involve running high resolutions over long distances, you may not need your HDMI cable to be as well-built as our Series-1. But if you are looking for a truly American-designed, primarily American-built cable that exceeds, from a technical standpoint, anything else on the market today, at a reasonable price, we hope you'll give us a try.

Product Specs and Description:

Signal conductors: 23.5 AWG, solid bare copper
Shielding, individual pairs: Aluminum foil bound to mylar tape, Z-fold, TC drain wire
Shielding, overall bundle: Aluminum foil bound to mylar tape, overlaid with 85% coverage TC braid
Pair and miscellaneous conductor dielectric: polyolefin
Outer jacket: PVC
Listings and ratings: cable was burn-tested by UL and rated CM (Communications). CM is superior to, and substitutable for, the more commonly seen CL2 and CL3 listings.
Overall diameter: 11mm (approx. 7/16 inch)
HDMI spec version: 1.3a
Attenuation (typical), per 100 feet:
825 MHz: 20.5 dB
2.475 GHz: 38 dB
4.175 GHz: 53 dB
Characteristic impedance of data pairs, per TDR, unconnectorized: 100 ohms +/- 3 ohms
Intrapair skew, per 100 feet: less than 140 ps
Interpair skew, per 100 feet: less than 2 ns

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