Ground Loops

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 extended our well-known precision digital video cables with a new product line (DNH Series) that exactly addresses this need. It is available in different colors and in all sizes ranging from Mini RG59, RG59 to RG6 and RG11. 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.

In fact, we recently tested one of our off-shore competitors who claimed to make identical cables to our precision digital video cables, like 1694A. Testing dozens of reels bought on the open market, not a single one got close to the 95% shield we make. Their closest was 84% and their worst was below 50%. I was talking to one of our engineers at the IBC show in Holland. “All you have to do is weigh the reel,” he told me. We all use the same plastics and same wire (pretty much), so if the reel is 20% or 30% less weight than the Belden stuff, well, that difference has to come from somewhere!

We know that customers are always looking for cost reduction and therefore we recently launched at IBC a new market performance video cable range (70000 Series) which meets the industry standards perfectly and is our best price/performance product. Together with the DNH Series the new 70000 Series is also designed to fit seamlessly with our 1-Piece HD BNC compression connectors. This combination will save more money, as it reduces installation time and labor cost!

If you have a foil and braid, you don’t need a drain wire. The braid is also the connection point for the foil. If you put on a BNC, you would make contact with both foil and braid, although the braid is the main mechanical connection. However, we do make one cable that has a braid shield and a drain wire. That is our top-of-the-line microphone cable, Belden 1800F. It has a flexible tinned copper French Braid shield, with a bare copper drain wire underneath. The drain wire makes it very easy to connectorize this cable. And it’s a different color (copper) from the shield above (silver-colored tin). You don’t have to separate and un-comb the braid. Just cut it off and use the drain wire. Simple! Here’s a picture of that construction.


1800F Read more »

CMRR: What is it and how do you get a good number?

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???” Read more »

A Look At Active Balancing

We’ve been talking in the last few blogs about balanced lines. These are cables or circuits where the signals travel on pairs of wires, or pairs of traces on a circuit board. With cables, the pairs are usually twisted together. On a perfect balanced line, the audio signal is equal intensity but opposite polarity on the two wires. Just think of it like cars on the racetrack. If you’re zooming down the track, and you look across to the other side, those cars are going in the opposite direction.

Just like a racetrack, the signal is a circle, we call it a circuit, and we call these signals differential signals because they are moving in different directions. The fact that we twist the wires together makes it difficult to recognize it as a circle, but it still is. Read more »

Balanced Lines

Do you know the difference between a balanced line and an unbalanced line? If we’re talking about analog audio, this difference between balanced and unbalanced is also the difference between consumer products, which are almost always unbalanced, and professional, which is almost always balanced. To go into the details of these differences would take a number of blogs, so I’m going to try and condense it here.

If you want to know more details, just invite me out to speak at your local group. Are you a member of the Society of Broadcast Engineers? Perhaps you joined the Society of Motion Picture and Television Engineers or the Audio Engineering Society. All three of these, and many other similar organizations, have local groups and often have lunch or dinner speakers. I would be delighted to fit you in my schedule and come give a presentation on balanced lines or many other subjects. Read more »

Wiring Up An XLR

Professional video connectors are crimped. But there’s one professional connector that is still soldered, the venerable XLR. It has become the universal standard for audio wiring. It is made by many manufacturers including Neutrik, Switchcraft, Amphenol and many others. You can even find some made by ITT Canon, who invented the connector in the early 1950s. And now Belden is working on a video to show you how to solder a mic cable (or a line-level cable) into this connector and will post it as soon as it’s available.


However, I wanted to add some comments which are not addressed in the video. Foremost is the tendency of some plastics to melt when heat is applied. And the problem is, the higher the performance of the cable, the more likely that plastic is to melt. The converse is equally true. The lower the quality (not the price, mind you, but the performance of the cable), the less likely it is to melt. If you have rubber insulated singles, such as Belden 8412 or our new super-strong 1776, you could hold a soldering iron on these wires for a long time. You might eventually burn through them, but it would take a while. Rubber, after all, is not a thermoplastic, it is a “thermoset” material.  Read more »

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