Belden HDMI Cable Update
We've had a lot of questions directed to us about our Belden HDMI cable project, and the purpose of this page is to produce an ongoing chronology and update as to just what's going on. If all you're looking for is the quick summary: we expect Belden-built cables for HDMI to be available approximately April of 2007, and as that date approaches, we'll be publishing pricing and other details.
The story of our HDMI project starts back in 2004, when we first inquired of Belden about the possibility of building HDMI cable for us. At first this project was slow-going; we couldn't promise Belden a lot of sales volume, and the HDMI configuration is a hideous mess which doesn't correspond well to any existing cable type Belden was manufacturing, so this cable would truly have to be designed from scratch. But we were assured by Belden's Business Development Manager Steve Lampen that if Belden knew it had a real live customer for the product, the product would get built.
With that in mind, I (Kurt Denke--owner and product development geek at BJC) decided to go and pay a visit to Belden, which took place in December 2005; I met with a team of product development engineers, including the head of product development, Martin Vandeburgt, and an engineer who had worked on a similar project, David DeSmidt. Between those two and the others present, we agreed to get together a spec for a test reel, to be built in Belden's state-of-the-art engineering lab. The Belden engineering lab is quite a place--it's larger, and has more diverse capabilities, than many companies' entire wire and cable factories.
The most important feature of the test reel was to be a proprietary Belden feature: "bonded pair" construction. In bonded pair construction, a twisted pair of wires isn't just two wires, twisted together. Instead, the twist is applied, and the dielectric is extruded over the pair, so as to make a single twisted structure. Where a conventional twisted pair can open up or tighten when cable is flexed, a bonded pair maintains a very stable, fixed relationship between the conductors. This construction was designed and patented by Belden for high-speed data cable, and we felt it was the perfect fit for this product--because the HDMI spec calls for extremely high bitrates to be pushed through twisted pairs (under HDMI 1.3, a deep-color 1080p signal can run up around 3.4 Gbps), and controlling impedance and return loss in such a cable is critical.
In ** of 2006, our test reel emerged from the Belden lab. We subjected it to a variety of tests, primarily in two categories: (1) tests of the type applied by an HDMI Authorized Testing Center, which are used to judge spec compliance, and (2) "in-use" tests, to determine that the cable functioned well and to get a good idea just how far a signal could be run in it. As you'll know if you've read our other articles concerning HDMI, it has been our view that the major factor limiting distance runs in HDMI cable is not, as the Chinese manufacturers seem to generally assume, resistance attributable to wire gauge, but is return loss, attributable to poor impedance control.
This initial sample reel was a roaring success; our in-use testing had standard-definition HDMI working on a Sony display and a variety of DVD players at 180 feet. The conventional high-definition resolutions, 720p and 1080i, kicked in somewhere between 100 and 140 feet, and at the time of that testing, we didn't have equipment that would support 1080p testing. One day, we had some factory reps from Mitsubishi in the shop, and they were asking about our HDMI needs for long-distance runs; we told them we had a working 180-foot HDMI cable, and they didn't believe it. When we plugged it in to demonstrate, one of them asked: "who builds your transceivers?" -- he didn't understand, or could not really believe, that this wasn't an active device with boosters, equalizers, or something of that sort, but was simply a straight, passive cable assembly.
The funny thing about that roaring success was that, as electrical testing showed, the cable still wasn't as good as Belden could make it. The impedance, as measured by TDR, came in at about 94 ohms, significantly off the 100 ohm spec. Why is that? Well, one of the funny things about designing a brand new cable is that the design dimensions have to be translated to production specs, and the actual impedance of a cable is more complicated than the formulas for predicting it will allow--so an initial sample is bound to be off-spec somewhat, and need correction. But that result provides a perfect baseline for adjusting the recipe, which David DeSmidt did on the next round.
On redesign, the cable was reconfigured slightly; the AWG of the signal conductors was increased just a bit, to 23.5 rather than 24, and the dielectric dimensions were adjusted to tweak the impedance to center around 100 ohms. These tweaks resulted in some very significant improvements in test results; return loss dropped about 10 dB practically across the board, and *****
We have ordered full production runs of the Belden Bonded-Pair HDMI cable, and of a high-flex version--a 26 AWG, non-bonded cable, suitable for shorter runs where flexibility is an important consideration. Now, this brings us around to another issue: cable assembly.
One of the factors that delayed our getting into the business of having an American-made HDMI cable produced was the problem of cable termination. HDMI is a nineteen-conductor rat's nest, and not simple to terminate. Moreover, on researching the available connectors, what we found was that they're all made to solder on. We found ourselves with a chicken-and-egg sort of problem. We needed a new termination system to deal with assembling these cables, because an American assembly technician doing 38 solder joints per cable just wasn't going to be a cost-effective way to terminate the cable; but without a supply of raw cable to work with, a lot of our notions about how we might terminate the cable were very hard to experiment with. We've looked at IDC (insulation-displacement, like a CAT 5 plug) connector possibilities, and ultrasonic welding, and "crimp-n-poke" systems, and we're still not quite sure what to do; but we are determined that, if it's feasible to terminate these cables in the US, using American labor, we will do so. Our reservations about the government responsible for the Tiananmen massacre--a government that still allows no meaningful political or economic liberty to its citizens--give us the strongest motivation to accomplish that goal.
But at the moment, there is no cable assembly house building HDMI cables outside of China. In fact, it's easy to figure this out just by looking at the list of HDMI Adopters. There are a lot of American cable "manufacturer" names conspicuously missing from the list. Why? Well, if all you do is buy your HDMI cable from one of the handful of Chinese assembly houses that build them, there's no reason to be registered as an HDMI Adopter. Since the names most people associate with interconnect cable are primarily marketing companies, not manufacturing concerns, and because their products don't involve the application of any new or different technology or processes to the manufacture of HDMI cable, there's really no reason for those companies to do anything but buy their cable assemblies from those assembly houses, mark them up, and resell them.
For the time being, the Blue Jeans Cable Series-1 HDMI cables will be manufactured as raw cable in Indiana, and then shipped to China for termination and final assembly. While that means our cable won't be 100% American-built, it still makes it the only cable on the market that's not even close to being 100% Chinese-built. About 10% of the total cost of the cable, on average, will be going to China (more on shorter cables, less on longer). But now that we have a reliable and ongoing supply of raw HDMI cable of known spec and dimensions, we are at last able to deal with the long-term issue: how to terminate this product in the U.S. without inflating the cost beyond reason.