The benefits of Fibre Optic technology have been experienced by those specifying and installing distribution systems for some time now. The unique nature of Fibre Optic transmissions makes them ideally suited to the distribution of signals across long geographical distances or where a large number of outlet points are required writes David Evans from dTV. Fibre has become the system of choice to prevent illicit interception of signals in situations where secured transmissions are essential. Fibre Optic cable is also well known as a low maintenance product with excellent performance in high ambient signal areas or where copper coaxial cable is likely to suffer from local environmental conditions.

So with all these benefits, why has Fibre Optic been regarded as a product of marginal interest to the professional installer? Until very recently, the costs associated with Fibre Optics have meant that practical uses have been only for very large distribution systems, typically trunk-links between distant towns. It may also be that the apparent complexity of the technology has deterred its more widespread use.

Simple but effective
In reality, a Fibre Optic system really has only three components. An Optical Transmitter, such as a Vision V100-TX6, is connected to Optical Cable, for example that distributed by Webro through Solutions Group. Optical signals are converted into Radio Frequency (RF) signals by an Optical Receiver (like a Vision V100-RX1) at the destination which then becomes compatible with standard domestic or commercial RF equipment.

With signal losses as low as 0.5dB per kilometre, several hundred times less than an RF signal moving along a cable, repeaters or amplifiers are not needed in order to keep up signal strengths. In fact, signal losses are mainly caused by connectors at either end, rather than the Optical Cable itself. The Optical signal will also be free from unwanted signal interference (known as “pick-up”) that may come from other transmission equipment or electrical power lines.

Diagram 1 and 2 show this advantage. The RF-only schematic in Diagram 1 has individual repeaters which must be fitted, balanced and maintained, with a highly variable signal strength over the entire length. This requires eight expensive repeaters over a 900 metres length. Imagine how many repeaters would be needed over 5,000, 10,000 or even 20,000 metres! The Fibre Optic version in Diagram 2 needs no such repeaters almost regardless of its cable length. The cost of installation and maintenance of repeater sites makes Fibre Optic distribution extremely viable.

Of course, there will be times when it is necessary to break into the trunk line to split an Optical signal. Vision V100-SP Optical Splitters are custom designed for the job, and can turn a single incoming Optical Signal into a two-way or four-way output to feed Optical Receivers in separate locations, (as Diagram 2 illustrates). Once again, losses along the Optical cable length are kept to a minimum.

Clear benefits
As availability and understanding of Fibre Optics increases, it seems likely that use in Integrated Reception Systems (IRS) will become more widespread. All the benefits seen in long distance applications are positive points again, but in particular long cable life, resilience to temperature and humidity changes, physical flexibility and the facility to be mounted in proximity to electrical cables make Fibre Optics just right for IRS work. The small outside diameter of a Fibre Optic trunk cable, compared to its coaxial counterpart, makes cable runs that much simpler. It may even be that existing ducts or cable trenches can be used to pass Fibre Optic through where extensive excavation work would be needed in order to run coaxial cables.

To contact the Digital Television Commercial Division for advice on how Fibre Optics can work for your IRS project, call 08456 444 000.

A97768 6dBm Fibre Optic Transmitter V100-TX6
A97785 3dBm Fibre Optic Transmitter V100-TX3
A9780 Fibre Optic To RF Receiver V100-RX1
A97819 2 Way Optical Splitter V100-SP2 A97836 4 Way Optical Splitter V100-SP4