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Glossary A


Alternating Current. Refers to a situation where current flows back and forth through a conductor (wire) in alternating directions. Generally, the voltage being applied to the conductor has a changing (alternating) polarity so the current has to change direction related to which end of the wire is positive or negative at a given point of time. In most cases we encounter, the voltage moves in a sinusoidal wave shape centered at zero volts, though it could be centered at another point. If it is centered at another point than zero volts, it is most often referred to as having a voltage offset. An AC voltage could have another wave shape besides sinusoidal depending on the application or components it is reacting with. The rate at which it changes direction is referred to as its frequency.

The opposite of AC is DC where the current only flows in one direction. DC will have a voltage level in only one direction, either positive or negative, referenced to a common, ground or zero volts reference point.

Mains power in many countries such as Britain, Australia and Europe is at 230v AC at a frequency of 50Hz, that is 50 complete cycles per second. North America uses 115v at 60Hz.

Accessory decoders

DCC decoders are used to control trackside accessories such as turnouts and signals using the NMRA standard pulsed signal. The signal can be carried by the track and track feeders or can be a separate circuit, which avoids the risk of a derailment or short preventing the control of the turnouts. All DCC manufacturers make accessory decoders and MERG provide kits.

Accessory encoder

The MERG DCC accessory encoder is designed to operate as a DCC command station independently from the track DCC although it uses the NMRA Standard for its information encoding and can operate most other accessory decoders as well as the MERG kits.


Address is the unique identification of anything. In the context of DCC it means the coding of each loco or other decoder, which ensures that it identifies the signals intended for it.


Agile is a Manifesto for Software Development. It aims to deliver working software quickly. See the Agile Manifesto and its history


An Amplifier is a device or circuit that converts a small signal, voltage or current, into a larger signal, voltage or current. Amplifiers are typically built from discrete devices like tubes or transistors, or are manufactured as a IC device to reduce components or complexity.

You will generally run into three amplifier types on the MERG forum or with MERG kits; a transistor as an amplifier, an Operational Amplifier (op amp) such as an LM324 or an audio amplifier such as an LM386.


Amplitude Modulation. The process of additively mixing a single or number of frequencies with the carrier wave to produce a complex waveform with variable amplitude. This signal may be demodulated by a simple diode detector. Most common method for low, medium and high frequency broadcast transmissions.


The unit of current. It is defined as the constant current which if maintained in two straight parallel conductors of infinite length, of negligible cross-section and placed one metre apart in vacuum, will produce between the conductors a force equal to 2×10-7newton per metre length.


A continuously variable signal. This is generally compared to a digital signal, which increases in steps or is conveyed by digital coding.


This is a Boolean operator which is used to join two statements so that the final statement is true only if the individual statements are all true. Thus (X>1)AND(X<2) is true if X is between 1 and 2. In electronic logic circuits an AND circuit is shown here.


Application Program Interface - A set of routines / protocols and tools for building software applications.


American Standard Code for Information Interchange Table of Codes
Wikipedia article


The name given to the appearance of a signal to the driver of a train. Each aspect is allocated a specific meaning so that the driver can decode the message and react accordingly. For example a semaphore home signal has two aspects, one with the arm horizontal meaning stop and one with the arm inclined meaning proceed.

Auto reverse

An auto reverse module is used in DCC to prevent shorts in reversing loops and other situations where the polarity of two lines must be reversed for a train to run through. It works by reversing the polarity if a short is detected. If the short is eliminated then the new polarity is accepted and is kept. One auto reverse module can protect several track sections provided that only section break is being bridged by a loco at any one time.


American Wire Gauge is a set of standard sizes for wire diameter. It covers both solid and stranded wire.

As the gauge number gets larger the wire diameter gets smaller. Larger wire is generally used for carrying higher current levels since larger wire has less resistance and so for higher currents less voltage is dropped over a given distance.

In North America, extension cords are generally wired with 16AWG or 14AWG. House outlet wiring would generally have 14AWG or 12AWG wiring. In the UK, Australia and many other countries 2.5mm or 4mm wiring would be used in a similar fashion. Bus wires for DC or DCC may use large gauges such as these to supply a fairly constant voltage level (provides a low voltage drop over distance) around a large layout. Feeders to a track would be much smaller wires as current demands would be smaller. Relay coils and small wattage transformers may have gauges from 18AWG down to 28AWG. Wirewrap wire is generally 26AWG. While this paragraph is fairly general, it will give you an idea what to expect for wire sizes on a layout or simple projects. Better detail and recommendations can be found elsewhere in the Forum for a specific task.

AWG is not the same as Standard Wire Gauge. There is no direct conversion in the ratio of wire diameter between AWG and SWG.

glossary/glossary_a.1568017554.txt.gz · Last modified: 2019/09/09 08:25 by tgerbic