Routing and Distribution Equipment

By Arthur Frunzhan

Review contents:

Routing and Distribution Equipment Auxiliary routing units of “Profitt” Company Multipurpose modules of Synapse system New line of distribution amplifiers from Extron Electronics Auxiliary routing and distribution equipment Kramer Electronics Leitch distribution amplifiers Devices of Marshall Electronics Company Routing and distributive equipment of Netrwork Electronics Company New HDTV Patch panels from Oxygen DCT IQ series modules from Snell & Wilcox Redbox series audio distribution equipment of from Sonifex Company Modular units from Thomson Broadcast and Multimedia Solutions The distribution equipment of Vistek Company

The word combination “routing and distribution equipment” is very frequent contacts greater matrix switchboards and video switchers which, undoubtedly, serve as a core of any TV system. However there are also other “fighters” of signal distribution front who practically are not visible, but without them the work of any complex is frequently impossible. These are auxiliary routing and switching centers: amplifiers-distributors, switching boards, processors, converters, adapters, etc. They allow to create the optimum and enough branched out infrastructure of TV complex and to provide the signal transmission there where it is stipulated by technological process of TV manufacture and broadcasting. This problem is not limited by signal transmission. It is necessary to support quality of signals during their transferring on different distances.

Amplifiers-distributors

Amplification and distribution (switching) of signals are the functions most widespread in electronics. Therefore the category of the devices named by amplifiers-distributors, is one of the most extensive.

Simplified block diagram of the distribution amplifier

The amplifier-distributor is not simple combination of the amplifier and the switchboard as it usually contains a set of amplifying steps — according with number of outputs, and also the entrance buffer limiting influence of inter component cables. The input is always single, number of outputs can be within the range of 2…20, sometimes is more. The most widespread versions are the following: 1×3, 1×5, 1×10. Sometimes there are models with two inputs, which are the coupled amplifier-distributors, for example 2×(2×10) with an opportunity of transition in the mode 1×(1×20).

As a rule, in this case amplification occurs on voltage, instead of on power and it objective is compensation of signal attenuation taking place on the previous sites along the path, especially in long cables.

The basic scope of amplifiers-distributors — video studios, broadcasting facilities, relaying units of the cable TV networks, presentation complexes, MultiRoom systems (with signal distribution to several consumers located in different rooms of single building). Various models of amplifiers-distributors can be intended for work with composite (full television) signal, and also with S-Video signals (chrominance and luminance are transferred by separate channels), component (chrominance and luminance signals are transferred on three separate channels), RGB (signals of three base colors transferred on three separate channels, plus black burst, mixed to the G signal), RGBS (the same, but black burst is transferred on the separate fourth channel), RGBHV (the same, but synchronizing impulses are transferred on two channels, of frame and line separately). The models intended for those or other signals, are provided with corresponding sockets: BNC for composite, component and RGB, and also vibi-DIN for S-Video. Popular household RCA sockets in professional components are not applied, as BNC provide the better coordination with 75 Ohm coaxial cable (sometimes 50 Ohm).

The correct handling with video signals demands a significant bandwidth which usually should be not less than 300 MHz, sometimes much more. In the latter case the device is also suited for transfer of the digital video signal SDI representing the digitized full television signal, as well as analog, transferred on the coaxial matched line. The working range of the video signals amplifier should begin from zero frequency that it was capable to pass a constant component (the name of this amplifier is direct current amplifier), or in it there should be a scheme of the constant component restoration.

As video signal is usually accompanied with a audio, audio amplifiers-distributors are produced also. Depending on their design and sockets they can operate with asymmetrical or with symmetric audio signals. In the first case the RCA sockets or terminal blocks, in the second — the same blocks, but with three contacts (phase, antiphase, ground) or special XLR sockets are used. Signals can move to the amplifier-distributor over usual two-wire line, twisted pair, and screened coaxial cable also.

More often video and audio parts appear integrated in one case of the amplifier-distributor, and groups of video and audio outputs are switched synchronously. The opportunity of work not with single, but with several signals (more often composite + S-Video) is sometimes provided. Transformation from one standard in another inside of the amplifier-distributor is not occurred.

The special group of amplifiers-distributors is consisted of devices with correction of parameters of signal which are much more effective and allow the operative adjustments to carry out. In the elementary case it is a loudness level regulator from audio part of the device, sometimes the frequency correction on high and low frequencies. In videopart the adjustments of chrominance and brightness are provided. There is very useful also a correction on HF with changeable depth: as reducing of high frequencies of the video signal spectrum is depended on cable length and coordination quality (on the oscillograph screen it is visible on dropped fronts and rounded tops of rectangular impulses), in each case the depth of such correction can be various. Restoration of constant component of video signal is also as claiming function: many devices connected in videopath may change its level which is completely restored in the amplifier-distributor.

There are also analog amplifiers-distributors of radio-frequency signal, capable to operate in high-frequency area corresponding their destination.

In sphere of transfer of digital signals the amplifiers-distributors are also widely applied: in local computer networks (LAN), integrated control networks, in digital TV, digital audio and videostudios, etc. Main requirement to such devices is a wide bandwidth as on outputs of the device the high-grade digital signal consisting of rectangular impulses with abrupt fronts which in process of passage over long lines of transfers become more flat because of what there is uncertainty of the moment of difference of levels (jitter) should be delivered. Thus, the device restores not only a digital signal scope, but also its frequency spectrum. Dimensions of digital amplifiers-distributors usually are the following 1×2, 1×4, 1×8, 1×16, etc. There are models with two selective inputs on 20 outputs, for example concentrators for Firewire interfaces, and also special devices for RS-232 interface. The special group is formed by amplifiers-distributors of digital video DVI which besides the basic functions should “be able” to carry out all operations connected with realization of HDCP-compatibility with other devices.

Amplifiers-distributors are active devices by definition and consequently power supplies are demanded. The last can be both as networking or as from adapter (voltage is constant). There are the stationary models of amplifiers-distributors mounted in standard 19" rack, and small-sized, “cut” on a place in the necessary section of cable network. The control can be remote either with board DU, or over interface RS-232, RS-485, etc.

Switchboards

This category of electronic devices — passive and active — is extremely wide and various. More often the switchboard has some inputs and single output that is reflected by its dimension (for example, 4×1). In the elementary case these devices are realized as usual push-button or turning switches. However to switch it is necessary not only the constant voltage and low-frequency (audio) signals, but also video, high-speed digital streams, therefore often it is necessary to address to more complex versions of switchboards containing buffer amplifiers-repeaters (amplifiers with the gain factor equal to 1) for uncoupling, relays or electronic keys, complex schemes of control with indication of condition, etc. As well as in case of with amplifiers-distributors, in models of switchboards there is often combined audio & video path providing synchronous switching of audio and video from different sources. Thus the audio path can be mono or stereo, symmetric or asymmetrical, and video — from composite up to component (and also digital). Sometimes there are some audio and video formats with corresponding sockets at once. Switching of video signal in complex models of switchboards is carried out not during any moment of time, but is synchronized with blanking frame impulse, preventing shakes and disturbances on the screen.

Operational principle of simple and matrix routers

Recently the increasing demand is found with programmed switchboards-scanners with many inputs (for example, 20×1), allowing to make “inquiry” of the TV cameras connected to the device in the necessary sequence with the set interval of time (as a rule it is necessary in systems of security video observation). Sometimes switchboards are provided with simple built-in device for scaling (scaler), allowing reducing to the general denominator the signals from computer (VGA) and video recorder (or from other storage). Such devices are very convenient, in particular in presentation complexes of the equipment.

As digital signals of the most different origin should be switched not less often, than analog, there is a whole group of corresponding switchboards for interfaces DVI, FireWire, RS-232, RS-485, etc. In digital switchboards the operation of re-clocking is carried out, that is transferring of digital data to the new, super stable clock frequency which is produced by means of the built-in clock generator with quartz stabilization. Thus the time errors introduced in a signal by jitter (phase jitter) are eliminated.

Besides actually switchboards, the combined models of switchboards/amplifiers-distributors are produced.

Controllers, panels and control panels

The devices from this category are provided for control as by separate components of system equipped by interfaces of external management, and by a whole system. There are the specialized controllers designed for certain switchboard or amplifier-distributor model or group of similar models, and also universal reprogrammable devices. There are can be push-button and touch control panels with the built-in or remote processor blocks, and also usual personal computer in which any necessary software is installed.

Video/audio processors

The functions which there are in this device group, are complex and various, as well as devices itself. Usually the processor has clear orientation concerning video or audio, and according to it can refer to video or audio processor. Video processors are carrying out a whole complex of deep transformations of video signal, in passing — mix and switching of audio signals. On the contrary, the audio processor is concentrated to audio processing; its video functions are reduced, as a rule, to switching. There are also exceptions: more updated models of the universal processors which are carrying out interpolation-based up-conversion of digitization frequency (up-sampling), digital processing of multichannel audio and decoding of Dolby, DTS, MPEG formats and so forth, offering thus a wide set of video options, including transcoding, format conversion, extensive control functions and adjustments.

Example of image parameters correction using processor

Modern processors are processed video in digital environment, therefore are provided by analog-to-digital and digital-to-analog converters, digital inputs and video outputs (SDI, DVI, HDMI) also. In any model of the processor from analog video formats can be presented only one (composite, component, S-Video, versions of RGB) or several, thus the processor is provided with corresponding sockets. There are also the universal models of processors provided by all types of sockets and converting formats by the following principle: “any on an input — any on an output”. Even more universal models assume transcoding, sometimes under following similar scheme: any of standards of chrominance (NTSC, PAL, SECAM and their updating) can be converted to another. At last, in some processors doubling lines and converting of interlaced scanning in progressive scanning is carried out, frequently with application of adaptive algorithms of correction of moving, and also interpolating scaling and control of screen format (16:9, 4:3 and etc.). For such devices the set of resolution values corresponding to various formats (SDTV, HDTV), to standards of chrominance and kind of scanning between which mutual conversion (both aside increases in the sanction, and aside reduction) are possible is indicated. Many processors enable to choose various values of frequency of line and frame scanning. Conversion of programs with interlaced to progressive scanning transferred from film in standard NTSC is carried out with 3:2 pull-down (thus superfluous semi-frames are rejected). Such signals are independently identified by special detector which will start the broach algorithm.

As a rule, the operative switching of inputs and distribution of signals at universal devices is provided, that is more frequently with external or internal synchronization (Time Base Correction, or TBC) for prevention of picture detriments at source switching. The resynchronization of R, G and B signals is also introduced which over long distance transfer can “slide apart” because of jet parameters of coaxial cable and little mismatches taking place in case of constructive defects of cables and sockets. Besides some models are provided by function of video signal multiplexing, realizing the screen partition into some fragments with independent pictures or placing of fragment of single frame atop of another with an opportunity of any movement of this fragment within the borders of the screen (various versions of an option “picture-in-picture” — PIP). The opportunity of correction of geometrical distortions of the raster arising at placing of projector on the not central axis to the screen is often provided also.

The powerful computing platform, which is characteristic for modern video processors, provides for work in real time a necessary speed, allowing to carry out the following conversions over above described, and operatively changes the video signal parameters also. The user can control of black level, dynamic range width, gamma-correction, correction of color transitions, and also of color, brightness, contrast, sharpness and saturation adjustment (in NTSC standard), of color temperature, levels of color components separately. Practically all video processors are provided by digital comb filter for the best partition of chrominance and brightness signals at “unpacking” of composite signal, and also by digital noise-reduction systems with several gradations of effect on a signal.

Usually the digital video processors have sufficient memory size needed for storing of various combinations of adjustments. As a rule, some ready presets are recorded into memory and each from these presets can be operatively chosen by the user and contains a whole complex of ready plant settings.

Control of processors is carried out via screen menu by means of remote control. Processors provided by RS-232 and RS-485 interfaces can be integrated into general control system and operate from central processor or computer.

Other devices

Besides all described above devices the passive devices, for example, switching panels are supplied widely also. Along with apparent simplicity they carry out the important functions of signal distribution. Therefore the approach to design and producing of these devices is careful similarly.