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I've spent some time in transmitter sites and I always have to shake my head whenever I find old audio cables running around. Typically they are packed with cloth, have a braided shield, thick insulation and, of course, only one pair of wires.

Thankfully wire and cable technology has come a long way since then, reflecting changes in the systems to which they become a part. Back in the day, at an AM transmitter site, most audio runs (if not all) had transformers on the source and destination. Balance and noise rejection were pretty easy, even in the presence of high-powered transmitters.

Somewhere along the line, single-pair cables with foil shields were introduced, such as the Belden 9451. These were certainly much easier to install than the old braided-shield cable. Another option was multiple pairs of the same type inside one fat cable. While these fat cables certainly saved time during the installation, they had the same issues as the single-pair cables: relatively high capacitance (34pF/foot at 1kHz). The cable was also relatively expensive; plenum rated even more so. Conduit runs had to be made large enough to accommodate multiple runs of the same type.

When the AES3 standard debuted, we had to start using cable with lower capacitance per foot, and due to the nature of the AES data stream, it became necessary to consider the characteristic impedance of the pairs themselves because they effectively became transmission lines. The AES3 standard is 110Ù, ±20 percent, for a balanced pair.

Fortunately for all of us, Ethernet came along with the CAT-5 and later the CAT-5e specifications. CAT-5e has a characteristic impedance of 100 (±15) ohms. Capacitance is specified at no higher than 17pF per foot. These characteristics made it acceptable for use in carrying AES3 signals around the studio facility.

While data cable has increased in common use, audio cable still sees frequent and sometimes abundant use in many facilities.

Now in the construction of a broadcast studio, you have the option of using cheap and readily available CAT-5e, CAT-6 or even CAT-7 wiring to handle everything that runs around the facility — whether it is dc, serial data, audio, AES3 signals or video. Oh yes — you can still use it for Ethernet, of course. Because there are so many applications for it, there are many companies that make it, thus driving down the cost. Because the twist of the wires is fine, and the balance in the pairs is designed to be good (keeping noise from being induced in the pairs themselves, and likewise, keeping the pairs from inducing noise in other nearby pairs) they can be tightly packed together and individual shields around the pairs are not necessary. This shrinks the cable because more pairs can be squeezed in a small diameter. The lack of shielding of individual pairs makes the installation substantially easier as well. This is the way the telephone company had done it for years, but far better.

CAT-rated cables

Belden Wire and Cable offers CAT-5e (7988R (for riser) and 7988P (for plenum)) and CAT-6 cable (7989R and 7989P) that can be used for carrying RGB or VGA signals because of its inherent low-skew 9ns for the CAT-5 and 10ns for the CAT-6. Belden also makes what it calls super-rugged CAT-5e patch cords. These cables can actually be tied in a knot and still pass CAT-5e data. Belden 1034A is the single-jacket, and 1035A is the dual-jacket for even more ruggedness.

Gepco International has its own version of ruggedized CAT-5e cable known as CT504HDX. This cable also is made with a dual-jacket, solid conductors and an extended bandwidth of 350MHz. The cable includes an inner belt that maintains the pair spacing and the electrical specifications while being bent or flexed. Gepco also makes a hybrid cable (RGB6c5) that contains coax (3GHz of bandwidth) and CAT-5e cables (350MHz bandwidth) in one jacket.

Clark Wire and Cable can provide Supercat, which is an outdoor CAT-5e cable suitable for direct burial, installation inside ducts or even lashed to aerial supports. The cable is fully flooded inside an abrasion-resistant and UV-resistant black polyethylene jacket. Optionally, this cable comes as STP with aluminum or steel shielding. Clark also provides CAT-7 cable with four shielded twisted pairs. This cable has a bandwidth of 600MHz and comes in plenum and non-plenum versions.

3M makes a CAT-7 cable called Volition. According to 3M this cable has reduced the pair twist on all four pairs, thus reducing the skew and making it perfect for gigabit Ethernet applications.

ETS makes a line of baluns (which are just transformers) to use CAT-5e and CAT-6 for various applications such as composite video and stereo audio (PV901) or passing RGB video (PV890). The company also makes balun/wall-plate combinations for simplified installation.

The Studio Hub wiring system from Radio Systems uses CAT-5 wiring as its backbone. The system uses a variety of connector panels and interfaces to route audio and data.

Obviously, there are other wire and cable applications in a studio facility as well. You can't do everything on UTP yet. For example, you will probably still need some version of microphone cable. There are plenty of fancy new types in that category as well.



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