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Blog Category: Broadcast AV

Posted by: Steve Lampen on January 13, 2014

The FCC (the US government bureau that controls radio and television) has issued thousands of new licenses for low-power FM (LPFM) radio broadcasting. Many of these LPFM's are schools, colleges, and universities. Still, others are small communities with little or no true local broadcasting. A lot of these are non-profit. The whole point is that there are thousands of new customers to the broadcasting brotherhood. Welcome! So now what do you do? I would bet a lot of these new broadcasters are new in every sense of the word. And this means there's a whole lot to learn about broadcasting.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on January 07, 2014

P. T. Barnum, of Barnum & Bailey Circus fame, was also the king of the "Sideshow" with strange and amazing things to see (many of which were fabricated). He's the one who said "There's a sucker born every minute!" At the end of the sideshow was a sign which read, "This Way to the Egress" which sounded like some exotic bird. Instead, the crowd found themselves outside, and had to pay another 25 cents to get back in. We talk about egress too, but instead of the crowd leaving the sideshow, we're talking about signals leaving the cable. I'll bet this is something you simply accept, that signals from one cable can interfere with things around it. And I mean a lot more than just interfere with other cables. I remember driving by one large windowless building in San Francisco during the 1970's. This was the computer center of a large bank. My AM radio would not work for a block in any direction from that monolith. Talk about egress!

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Blog Category: Broadcast AV

Posted by: Steve Lampen on December 31, 2013

One of my favorite jokes is about Belden 1800F. This cable is our top-of-the-line for microphone cable. The reason is simple. With analog cable, the key parameter is capacitance. The lower, the better. And Belden 1800F is 13 picofarads per foot (pF/ft.). That's even lower than Category 5e or 6 or 6a (15 pF/ft.).

However, Belden 1800F is also 110 ohms impedance for use with digital audio. In fact, this cable started life as digital audio patch cable. It was a high quality cable that is very flexible, and came in many pretty colors. It says right on the cable, "digital audio". If your customer says, "I can't use this on my analog mics because it says 'digital audio’," there's no problem. I will personally send you a bottle of rubbing alcohol. With that you can rub off the word "digital" and the cable works PERFECTLY after that.

It's not what it says on the cable, it's what is required to run that signal. The table below shows various parameters for different kinds of signals.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on December 17, 2013

A week does not go by without a customer asking for a combination of power and signal, such as power + audio, or power + video, or power + data (or some combination of these). Now, as you can imagine, there's almost nothing that Belden can't make. We could easily make such a cable. The problem is not how to make it. The problem is liability. If this is 120VAC with any other kind of signal cable next to it, it is illegal in the USA. And by illegal, I mean the UL (Underwriter's Laboratory) and NEC (National Electrical Code) won't allow such a combination. The reason is simple. If a forklift runs over the cable, and mashes it all together, then you have (or could have) 120VAC on the audio, video or data cable as well. I'm sure you have read all those stories of someone picking up a mic cable only to get electrocuted. Well, this is one way it could happen.

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Tags: Power, DC Power

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Blog Category: Broadcast AV

Posted by: Steve Lampen on December 10, 2013

One of my mentors passed away a few days ago, Roy Trumbull. For many years he worked at KRON-TV Channel 4 here in San Francisco. When I first joined the Audio Engineering Society in 1969, he was a member and helped me along. When I joined the SBE in 1979, he gave me my certification exam. He was also a man with a thousand funny stories about broadcasting. In his memory, I would like to share one with you. The names have been omitted to protect the guilty.

Television came early to San Francisco. One of the early broadcasters put their new transmitter at the top of one of our fanciest hotels, on one of our famous San Francisco hills. I'm sure it was line-of-sight to most of the Bay Area from there. The transmitter was of the water-cooled variety, where water dissipates the heat from the tubes. Cool water would be pumped in, it would pick up the heat and be pumped back out to a holding tank where it would cool and the process repeated. If you were a maintenance engineer, one of your jobs was to check the water level. Of course, a little always evaporated, and the hot water evaporated even more quickly. So you would pour a small amount of water to bring up the level. After only a few months, opening up the reserve tank was a nasty experience. All sorts of airborne things would love the warm water and would grow in the tank.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on December 03, 2013

I was talking to a friend of Belden's at a recent trade show. We were discussing using Category cable for audio, something we have discussed at great length in this blog. "I never use that cable for audio," said the customer.

"Why not?" I asked.

"Well, all the install Cat 5e or 6 or 6a is solid conductor," he replied. "And we all know that solid conductors break."

He was especially insistent that those solid conductors, when soldered into an XLR, often break. This is called 'work hardening'. Do you believe that? If you do, it probably means that you've been using some very cheap cable, because wires that break are not annealed correctly. One of the things you get with good quality cable and good quality manufacturing is annealing. Annealing is a process where the conductor is put into a hot oven to let the molecules come in contact with each other after the drawing process (big wire drawn into smaller wire), but not hot enough to melt the copper. Cheaply made cable sometimes rushes this process or does not anneal at all, creating a brittle wire that will break with just a few flexes. Everyone remembers bell wire from the hardware store. Probably not annealed at all.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on November 19, 2013

While I was recently in Amsterdam, the home of IBC, the European version of NAB, someone handed me one of our European competitor’s catalogs. It showed the distance their cables can go at HD and 3G (2K). Funny thing though, they didn't mention anywhere about the SMPTE formula (-20 dB at half the clock) which is the formula by which we at Belden determine the recommended distance of our cables. In fact, we can generate these numbers before we even make the cable. These are "safe distances" and are about half way to the digital cliff. I say "about" because, as chips improve, the effective distance keeps getting longer and longer. It is a common complaint we get, that you can go twice (even close to three times) the distances we show. Yes, those "recommended" distances are intended to keep you safe. Slap on connectors with the same bandwidth and return loss and you're good to go.

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Blog Category: Broadcast AV

Posted by: Steve Lampen on November 12, 2013

If you work with any kind of cable, certainly audio and video cables, then you are familiar with the shields in these constructions. Some are braid shields, good at low frequencies, starting at 1 kHz and slowly deteriorating around 400 MHz. (The openings in the braid structure begin to look bigger and bigger at shorter wavelengths.) Then we have foil shields. These are superior at high frequencies, starting around 10 MHz and going as far up as we can go. (Up to 20 GHz in some designs.) The foil is too thin and fragile to use it as a connection point, so, if you only have a foil shield, we give you a drain wire, a bare wire touching the foil that is your connection point. The ideal shield is a combination of foil plus braid. And the best of those is the highest braid coverage (around 95%) with a foil underneath.

You can even improve on that. A tri-shield, with an outer and inner foil, and a 95% braid in-between, is even better shield effectiveness. We have one digital video cable like this, Belden 1794A. Quad shields (foil/braid/foil/braid) would probably be even better, but I don't think it has even been tried with two copper 95% braid shields. It would require special connectors since the cable would be much bigger. If you know quad shielding, it's probably in the broadband/CATV world, where the two braids are 40% and 60% coverage, and are made with aluminum wires. This low braid coverage makes a huge difference in shield effectiveness.

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