Patch panel
From Wikipedia, the free encyclopedia
A patch panel or patch bay or jackfield is a panel, typically rackmounted, that houses cable connections. One typically shorter patch cable will plug into the front side, while the back will hold the connection of a much longer and more permanent cable. The assembly of hardware is arranged so that a number of circuits, usually of the same or similar type, appear on jacks for monitoring, interconnecting, and testing circuits in a convenient, flexible manner.
Patch panels offer the convenience of allowing technicians to quickly change the path of select signals, without the expense of dedicated switching equipment. This was first used by early telephone exchanges, where the telephone switchboard (a massive array of patch panels) and a large room full of telephone operators running it was ubiquitous.
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[edit] Uses and connectors
Patch panels are not only used in telephony and data, but in other audio and video applications. Patch bays are used at installations where it is necessary to connect and reconnect various hardware devices, for example at technical control facilities, patch and test facilities, at telephone exchanges, broadcast studios, and recording studios.
Patch panels can have any number of different types of electrical connectors, often having a different type on the front than the back. If it has a compound connector on the back and individual ones on the front, it is also a breakout box. One example is a DB25 connector used for 8-channel balanced line audio, which is split into eight XLR or TRS connectors on the front.
Patch bays facilitate flexibility in the use, routing or restoration of a variety of circuit types, such as dc, VF, group, coaxial, equal-level, and digital data circuits. Patch panels accepting industry standard keystone modules are also available, allowing a variety of connectors to be used on a single panel.
In telephony and data, the 66 block and 110 block are punch blocks often used as patch panels. These have insulation-displacement connectors for quick wiring of wires which have no attached connectors. Old switchboards used tip-ring (TRS) connectors on the front, still the most common type used now for audio.
While circuits were traditionally connected with short patch cords, in some implementations routers are now used to make the connections and handle numerous, instantly VT recallable configurations.
Patch bays may add expense to the amateur or semi-pro but are an essential feature to professional installations. While routers are gaining in popularity they are, more often than not, wired with the patch panels as a mechanical backup.
Video patch panels are required for the manual routing of SDI (Serial Digital Interface), HDTV (High Definition) or analogue L-Band at the transmission stage. There are a variety of connectors used for this purpose, some of which are self normalling while others require the use of U-links. They typically present a signal on the top row of connectors with a corresponding receiver on the bottom row. They are wired so in normal use the connection is made top to bottom by either internal wiring or external U-link. The path can be broken or re-routed as required. These panels can also be used for the Dolby 5.1 digital audio signal.
Audio patch panels are wired using the same principles but different signals. The audio signal can be analogue or AES/EBU (digital). Analogue and AES/EBU can be wired in the same format (using digitally rated cables where required) but three wire balanced systems are a necessity for common mode rejection (hum) in any large/professional analogue installation.
[edit] Normalling
Patch bays may be half-normal or full-normal, "normal" indicating that the top and bottom jacks are wired together internally. When a patch bay has half-normal wiring, its switching contacts flow through the bottom jacks of the bottom row while connected to the top row; plugging into the output connection will split the signal. If a patch bay is wired to full-normal, then it includes switching contacts in both rows of jacks.
[edit] Switches
Dedicated switching equipment can be an alternative to patch bays in some applications. Switchers can make signal routing as easy as pushing a button, and can provide other benefits over patch bays, including routing a signal to any number of destinations simultaneously. However, switching equipment that can emulate the capabilities of a given patch bay is much more expensive.
Example: a 16-point S-Video patch panel, with 8 patch cables, may cost $300.00, and connect 8 inputs and 8 outputs. An S-Video matrix routing switcher with the same capability (8x8) would probably cost between $2,000.00 and $4,000.00 new, though it would probably have more capabilities, including audio-follow-video and built-in distribution amplifiers.
There are various types of switchers for audio and video, from simple selector switches to sophisticated production switchers. However, emulating or exceeding the capabilities of audio and/or video patch bays requires specialized devices like routing switchers and matrix routers (aka "crosspoint switchers").
Like patch panels, switching equipment for nearly any type of signal is available, including analog and digital video and audio, as well as RF (cable TV), MIDI, telephone, networking, electrical, and just about anything else.
Switching equipment may be electronic, mechanical, or electro-mechanical. Some switcher hardware can be controlled via computer and/or other external devices. Some have automated and/or pre-programmed operational capabilities. There are also software switcher applications used to route signals and control data within a "pure digital" computer environment.
Distribution frames are cheaper, but less convenient.
