General Description
This signalling system provides both way working over audio line plant where a metallic path can be provided end to end. The system operates by regulating the direction of line current (commutation) to achieve recognisable signals over long lines. The use of line current reversals counters the effect of high line capacitance.
DC10 may be used over 2 or 4 wires.

Although SCDC is compatible with SSDC10-A it does not provide:
1. Delayed Dialling
2. Proceed to send
3. Forward Auxiliary Signal
4. Backward Auxiliary Signal

Transmission Requirements
To ensure the satisfactory recognition of signals the line characteristics must fall within the following limits:
Signalling path loop resistance 0 - 3.8k ohms
Signalling path CR value 0 - 42000 pf
Signalling path insulation resistance. Greater than l00Kohms

It can be assumed that these limits are met on BT lines when the two ends of the circuit are within 11km radial distance. (Subject to survey of the route)

Methods of Testing a DC10 Circuit
With circuit at idle and disconnected you should test a resistive loop into the local end. Testing towards the distant end will also produce a resistive loop.
When the circuit at the local end is seized the test conditions will change to 'earth A leg' and 'battery B leg'.
Dialling produces reversals of line polarity.

Not in general use today.

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Last revised: December 18, 2010