New technology in cables for studies in the digital and HD world

In both cases (audio and video), the construction was simple. It consisted of a driver of copper (bare or tinned) of sufficient caliber for minimize losses and adequate armor for the environment. The changes have affected even cameras using cables triaxial and multicore, and old cables can work up to a certain distance or possibly not working.

Today, SMPTE standards for video and AES/EBU for audio, specify a number of parameters critics that we have to respect. To begin with, you have to calculate the distances of the total system between studies, between panels, and equipment on both sides. That calculation must include each endpoint because each contributes no only to total losses, but also to reflection total. It is interesting to remember that a single poorly made connector, made with the wrong tool, or with defect of construction, can affect the signal.

To meet the needs of the digital and HD systems, cable and connector manufacturers had to use new materials and processes, and design products with scope. In many cases the difference is not noticeable on the outside, but inside there are big changes.

In the case of video, a cable is needed that has not only low losses up to the limit of the signal bandwidth band, but also one that has low reflection and a very constant impedance of 75 ohms for that frequency band. It is true that it is possible to use some of the old analog cables for digital signals, but only with short distances. However, cables can be used digital with analog signals without problem. In Table 1, you can see the approximate distances for several cables typical with signs of common norms. For HD signals 1080p, a typical RG6 cable like Nemal #1580 or Belden 1694A does not it passes more than 100 meters. Therefore, the obvious solution in that case will be to use fiber optic cables. With single-mode fiber cables, HD signals can be transmitted for kilometers, almost without loss. It's really the cable of the future, but still the Equipment price can be expensive.

Coaxial cables designed for Digital and HD are distinct from the old generation in several aspects such as the type of conductor, the type of dielectric, the type of armor, and the cover. All of those factors affect one. to the other and the cable selection, in many cases, is a commitment of these variables. For example, the losses of a larger cable is usually smaller, but the cable is more heavy, takes up more space, and comes out more expensive. To get to the minimum possible losses, we use a dielectric made of polyethylene with gas injection. With that technology, increased the propagation speed from 66% to 83% (typical), giving a great reduction in losses and capacitance. To the at the same time, that dielectric is much looser than the solid polyethylene, and more susceptible to damage to the installation.

A cable that passes from one floor to the other, in many cases, you must comply with the electrical codes of the state against fire and smoke. Armor is more critical of the digital signals and so instead of one or two copper meshes naked, as in the past, the typical construction now is a tinned copper mesh and an aluminium tape. That works. to protect the cable from RF interference (mainly with tape above 10 MHZ) and also interference below of 10 MHZ as motors and other electrical appliances, (mainly with mesh). The conductor of a coaxial cable Digital is usually solid bare copper to maintain low losses by the total frequency band. Is different from some RF cables that are copper with center of steel. Steel gives more strength but also more strength to low-frequency signals traveling in the center. The RF signals don't show that problem because they travel mainly on the surface of the conductor skin effect.

With cables for use on the move, there is constructions with braided copper conductors. That gives a life longer and makes the cable more flexible, but increases the losses. With any of the drivers, it is indispensable maintain the position exactly in the center of the cable. With foam dielectric, it is more difficult, but there are processes of production to minimize that problem.

Another common dilemma in the installation of coaxial cables for HD, is the use of clamps. One very nice installation with clamps at fixed intervals with too much tension will create a reflection on a frequency in particular, depending on the interval. It's a difficult problem to find and several engineers have spent a lot of time and energy looking for problems in equipment that don't really Exist. All that means that you have to be more careful in the installation of digital cables.

In the case of audio, there are two options Main. First, digital coaxial cables can be used with transformers of 110 for 75 ohms on both sides. That gives the luxury of having a type of cable, connector and tool, and it usually saves the time of assembling the connectors. In many Cases, a special color is used to differentiate the cables from audio of the video. However, the cost is higher. The another option is to use a digital audio cable, typically of a pair of caliber 24, bullet line, armored with tape of aluminium. This cable has some of the same limitations physical than the video cable. The AES/EBU standard is for a impedance of 110 ohms and has a bandwidth depending of the rhythm of the sampling rate signal. The Standard has a tolerance of 20% (88 to 132 ohms). Other possibility is to use, in certain systems, category cable 5e/6.

Fiber optic cables (SMPTE Standard) 424M), offer performance unimaginable with copper cables. For example, reflection on a digital copper wire can be from 15-20db and in a fiber cable it reaches more than 40db. The Losses are very low but the cable can be fragile. Up to a little dust on the connector can stop the signal. The standard SMPTE for HDTV camera cables is for a hybrid cable with 2 9 thousandths of an inch single-mode fiber for video and 4 copper conductors for data and feeding. The design of the cable has improved a lot in recent years, but not yet it has the strength of triaxial cables. The installation of connectors is not easy, and requires training and special tools.

The digital world of HDTV is here and with a little preparation and planning in the selection and cable installation, we can offer a signal quality never before possible.