Analog Conversion

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Short Definition

Allows a locomotive with DCC decoder to run on non-DCC powered tracks.

Analog Conversion is a mode of power conversion that is supported by most mobile decoders to allow a Digital Command Control decoder equipped locomotive to operate on a non-DCC equipped layout.

It is defined as optional by the NMRA Digital Command Control Standard. It is not the same as Zero Stretching.

How It Works

Analog Conversion is an optional feature provided by a mobile decoder when it is operated on Direct Current supplied from a traditional analog controller. The DC voltage level must be sufficient to power up the decoder circuitry (usually only a few volts) so that it can operate. In the absence of a DCC signal, the decoder will default to driving the motor in the same direction as the polarity of the DC supply indicates. As the supply voltage increases the decoder will supply more power to the motor so that speed increases accordingly. When the direction is reversed on the analog controller, the decoder will correspondingly reverse the direction of the motor.

Different decoders may handle different analog controllers with varying degrees of success because many analog controllers do not simply vary the voltage to vary the speed. Some of them employ PWM or other techniques to modulate the motor speed to improve low speed performance.

Many mobile decoders will support automatic function controls in analog conversion mode. For example, only lighting the headlight in the direction of travel.

Set Up

Analog conversion is not required by the NMRA standard but the method of enabling it is. CV29's bit 2 must be turned on. By default it is usually off. This bit means Enable Power Conversion. The NMRA standard allows for multiple types of power conversion and analog is only one of them. For decoders that support multiple types of conversion CV12 should be set to 1 for analog conversion.

See the article on Configuration Variables, as NMRA defines a number of optional alternative power modes, such as Hornby's Zero 1 or CTC-16.

Many users set the decoder to NMRA DCC Only, so if a decoder will not respond on a DC powered layout, check the decoder parameters are set to allow operation on analog power. This is done to prevent runaways should an unexpected condition occur on a DCC layout.
As always, read the manual for your decoder.