Specifications

7SR242 Duobias Data Communications

2.1.3 Fibre Optic Interface

When connecting via the optional fibre optic interface the selection of fibre-optic cable is important. Fibres must

be terminated with STTM (BFOC/2.5) connectors.

The recommended type is 62.5/125μm glass fibre. Communication distances over 1 km are achievable using this

type of fibre.

The fibre optic data comms link will be interrupted if the relay element is withdrawn from the case.

A budget loss calculation should be made for all installations. The following table gives the launch power and

receiver sensitivity of each of the fibre optic communication ports on the Argus M relay when used with specific

fibre optic types.

Tx Launch Power (dB) RX Receive Sensitivity (dB)

Fibre Type

Min Max Min Max

62.5/125μm -11.7 -15.7 -24 -9.2

1mm Polymer -6.4 -10.4 -24 -9.2

200μm PCS -2.8 -6.8 -24 -9.2

Factors to be considered when calculating fibre-optic transmission distances:

x Transmitter launch power

x Attenuation, based on light frequency, fibre material and fibre diameter

x Number of intermediate connectors and splices

x Receiver sensitivity

x The light power at the receiver must be above the sensitivity of the receiver in order that effective

communication can occur.

x Fibre cables are supplied on reels of finite length which may necessitate additional jointing.

x Typical losses at connectors are 0.5-1.0dB each. This allows for normal age related deterioration.

Consult manufacturers data for actual values.

x Typical Splice losses are <0.3dB.

x A 3dB safety margin is usually allowed after the budget calculation is performed.

Following installation and prior to putting into service the actual losses should be measured for each fibre using a

calibrated light source and meter. Measured and calculated values can be compared.