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The Radio Design Labs Format-A system uses standard, IT, networking cables to send receive and distribute audio signals. As a result, systems may be installed in existing bulidings using the existing flood wiring, thus avoiding the cost, damage, and the consequent making good, of installing fresh cable. Alternatively, and perhaps even more effectively, in a new build or refurbishment project, the neccessary cable runs can be specified by the audio technical team but installed by the team who are wiring the building for telephones and IT.

Where the cable is to be connected to a wall-plate, at the second fix the audio installer simply crimps a standard RJ45 connector onto the wire and plugs it into the rear of the RDL plate. Cables terminated with an RJ45 socket outlet may even be terminated by the IT team, leaving the audio installer simply to plug a standard network patch lead into the socket provided and into the RDL equipment.

The Format-A scheme uses cables with four twisted pairs in one jacket. Of the four twisted pairs, in a Format-A system three pairs are used for audio; the fourth pair is used to supply 24V DC power from the sending end or intermediate node to active panels which need power. Old category 4 cable may be used in existing environments, but most modern installations will have Cat 5, Cat5e or Cat6 cables, all of which are suitable.

Sending and receiving modules are equipped with connectors and terminal blocks for 'standard -10dBV unbalanced and +4dBu balanced line levels' and 'standard microphone levels'.

Sending unbalanced signals, directly from such equipment as CD players, over more than a few metres of unshielded cable would normally have undesirable resuts such as attenuation of high frequency content, interferance and hum. Sending microphone signals, even if balanced, alongside line-level signals in the same cable can often result in crosstalk interfering with the microphone signal.

Multiple line-level signals in the same cable, however, are often sent very long distances indeed. A major UK broadcaster, for example, at one time had need for 24 mono audio signals to be monitored in many technical areas, in many different parts of the building. This was accomplished using a single 25-pair cable to each location, fed and received by high-quality, balanced, transformer circuits. Cable lengths of over a kilometer were common. Crosstalk, distortion and high frequency loss were not a problem.

RDL avoid these problems in the Format-A system by using balanced sending circuitry to drive the twisted pairs and balanced receiving circuitry to isolate the signal on the twisted pairs from the external connections.

Format-A modules are available for mounting in walls, cabinets, racks and at other convenient locations. Each module may use a single pair, two pairs or all three of the audio pairs in a cable.

Single-pair products allow the installer to select which of the three pairs is used to send or receive the signal. Two-pair products are used for stereo audio. Three-pair products send and receive three separate signals which may comprise three mono signals or microphone plus stereo line signals. Modules that do not use all three pairs are equipped with two RJ45 jacks, allowing senders and receivers to be 'daisy-chained'. 'All products are compatible with RDL twisted-pair power inserters and signal distributors'.