FAQ:Can an unmodified locomotive operate together with a DCC locomotive at the same time?

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The NMRA DCC standard allows for this, although some care needs to be exercised in its use. The DCCWiki refers to this type of operation as analog compatibility mode. The signal is symmetric around the 0-volt level which provides a 0-volt DC component. By expanding the length (period) of the zero-bit applied to one rail, the resulting current flow will generate enough torque in the motor. The long period of the zero-bit results in an average DC voltage which determines the speed of the motor.

DCC waveform demonstrating Zero Stretching

The direction of the vehicle is determined by which rail receives the expanded zero bit(s). Be advised that this technique can create excessive heat in the motor. As a rule, a locomotive without a multifunction decoder should not be left on the layout as the DCC signal can cause overheating of the motor.

Some high precision motors (the ironless core type) may be permanently damaged. (See the following question.)