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Blog Category: Broadcast AV

Posted by: Steve Lampen on January 29, 2013

Our previous blog, Twisting the Night Away-Part 1, discussed the history of twisted-pair cable for data. (Click HERE if you missed it.) We had gotten up to Category 5 with the key takeaways being that the twist lay of each of the pairs is critical to the quality of performance that can be delivered by the cable, and that even if you get that right, installation issues can throw off the twist lays and degrade performance.

To address this issue Belden introduced a new approach: Bonded-Pairs. The pairs were extruded, twisted together, and the two insulated (and color coded) wires were fused together, without glue. This meant, when such a cable was bent or flexed, the pairs did not separate and the lay lengths did not change. (There are many other advantages to Bonded-Pairs which we will deal with in future blogs.) Bonded-Pairs are a Belden patent, so don't expect to see them anywhere else. Competitors will tell you that it adds time to each install. Sure, but it also gives you the ultimate in performance-AFTER-installation.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on January 17, 2013

If you've ever played around with Category cables, such as Category 5, 5e, 6 or 6A, you might have noticed that the pairs in these cables are very precisely twisted. And, if you've got good eyes and look closely, you'll notice that the four pairs inside these cables are all twisted differently. The length of the twist is called the "lay length" so each pair has a different lay length. How we twist them, and how we decide what they lay length each pair should have is an interesting story. The TIA subcommittee that decides about "Categories" is called TR 42.7. (They're currently working on "Category 8" for the next generation 40 gigabit cable, 40GBASE-T - no kidding!) When they were first formed, in the early 1990's, it was decided that any twisted pair, such as POTS, "plain old telephone service," was Category 1 and any cable made specifically to run low speed data was Category 2. The first cable design they worked on was Category 3. It had a bandwidth of 16 MHz (the same bandwidth as IBM Type 3 Token Ring cable on which Category 3 was roughly based).

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Blog Category: Broadcast AV

Posted by: Steve Lampen on January 10, 2013

It may be that when you read the title of this blog, "Waterblocking" that you thought to yourself, "Isn't ALL jacketed wire and cable waterproof?" The answer is "No." Almost every jacket compound, from PVC to Polyethylene to Teflon® is at least water resistant, so they can get wet and then dry out and they cables would probaby be okay. It really depends on how much time they spend in water, and what kind of exposure they might have. For example if your cable is on the outside deck of a ship, that would require a lot more waterblocking protection than inside a rack room. The real problem is when a cable is in standing water which doesn't go away. An example of this could be a conduit filled with water goes all the way to a lake in a theme park. Water is often called the 'universal solvent': given enough time, it will get through anything. Water can easily work its way through polyvinyl chloride (PVC) which is the most common cable jacket material. A cable underwater with a PVC jacket maybe has weeks, or a few months, before it fails. The first step toward long-term waterblocking is a better jacket material such as polyethylene (PE). This is much more water resistant, especially if it is high-density PE, and may last many months, even years, underwater. But there is one more step you can take, and that is to specify that the cable has a 'waterblocking' layer.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on December 20, 2012

'Twas the night before Christmas, when all through the station
Not a DJ was playing (they were all on vacation);
Automation was humming, everything working
And a fresh pot of coffee was already perking;

The engineer nestled all snug by his workbench,
At the ready were his screwdrivers and Allen wrench.
He settled back, with nary a care
When suddenly........ they went off the air.

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Tags: Holiday

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Blog Category: Broadcast AV

Posted by: Steve Lampen on December 13, 2012

The #1 bone of contention with my wife is number of MAGAZINES get delivered to our house. I get around 40 different magazines each month. Since I am on the road a lot of the time, I never get a chance to read them all, so the pile builds and builds next to my chair in our living room. Every so often, as I did last week, I just throw them out unread. I really want to read them. I really do. But if they're six months or more out of date, I've missed the boat already. But every so often, I pick up one and read something interesting. Here's a quote from an article on studio installation:

Studio wiring is typically time consuming, complex and represents a good portion of a new studio build expense. Analog cables are susceptible to RFI/EMI emissions and grounding issues. Even the “cleanest” installations cannot avoid cable capacitance or “skin effect” associated with long cable runs that deteriorate signal performance.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on December 06, 2012

Phew! Another long tradeshow season is behind us! Reflecting on this I remember how in the old days I would often stop at the booths of manufacturers of consoles and mixers with a simple question, "What is the CMRR in your inputs and outputs?" I would get one of three responses. Those truly world-class manufacturers would tell me, "I know what that is...," and look it up in the Owner's Manual or Installation Manual for that console. The second response would be, "We'll get back to you...," and then they would go off and figure out what CMRR is. The third response, from those inexpensive mixer manufacturers, was, "Huh???"

So what is CMRR? It stands for "Common Mode Rejection Ratio". It's a number that describes how well an input or output will reject noise, or how well "balanced" a balanced line is. So to understand CMRR, you have to understand what a balanced line is and how it works. It is relatively easy to calculate CMRR, it is a logarithmic scale and is expressed as so many dBs of level. It calculation comes out as a negative number and describes how "deep" the noise is compared to the actual signal. (If you read my blog on balanced lines, you could also say that CMRR describes the level of the common mode noise compared to the level of the differential signal on a pair of wires.)

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Blog Category: Broadcast AV

Posted by: Werner Eich on November 12, 2012

Last month I visited a leading system integrator for TV studios and outside broadcast (OB) trucks. It is always impressive to see how full these trucks are packed with equipment for audio, video, intercoms, air conditioning and satellite dishes – and don’t forget the workspace for a crew of up to 25 people! Everything needs to be well thought-out to be clean, compact and super-efficient. In the end, this is a fully functioning professional TV studio on wheels… with two limitations: one, there’s much less space than in a permanent creation, production and delivery area; and two, there are the over-the-road axle weight requirements.

The OB truck that I saw will be used, once it’s finished, for football events only. For this kind of application, HD production has become a standard, but the system integrator also has to take into account the fact that the video signals can be run on 3D cameras as well. With each new OB truck they outfit, they further fine-tune and improve the design, equipment and capabilities, based on their experience with preceding trucks and changing end user specifications and applications.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on October 24, 2012

The first AES (Audio Engineering Society) convention I ever attended was 1968 in Los Angeles. At the AES that year were a dozen or so exhibitors. One was a guy named Ray Dolby who was showing his revolutionary "Type A" noise reduction, one channel of which took maybe 7 rack units?! Across from him was Paul Klipsch showing his "Heresy" bookshelf speaker (since he only believed in horn loaded speaker designs). Of course, I didn't know that I was seeing history in the making, that these people were the icons of audio. How little we know when we are young and foolish. (Now I am old and foolish.) I snuck in to the AES show in 1968. I joined AES in 1969.

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