Electrical "Odds-n-Ends" for Model Railroading Enthusiasts                         

As printed in O Gauge Railroading August 2002 issue:

The Magic Lamp by Richard Melvin

"In every electrical circuit there are a couple of electronic parameters called 'capacitance' and 'inductance'.  The combination of these two parameters establishes what is called the 'impedance' of an AC circuit.  Too much of either one can cause problems by creating an 'impedance mismatch'.  The result is the circuit becomes less efficient and does not carry signals well.

"The jumble of wires under the typical train payout is a highly capacitive network with very little inductance, which creates an impedance mismatch.  When the DCS signal is fed into this network, it weakens rapidly.  DCS users who improved the situation by adding light bulbs were unknowingly adding inductance to their wiring network, brining the network back into a better impedance match. 

"An inductor is nothing more than a coil of wire.  The filament of a light bulb is a tightly wound coil of wire that glows brightly when current is applied to it.  Placing light bulbs into the wiring adds an inductive load to the network, canceling our some of the excess capacitance and setting up a better impedance match.  This is why adding the lights improves the DCS signal propagation.  Often the DCS performance can be improved simply by connecting a light bulb to the output terminals of the TIU or to the input terminals of the MTH terminal strip, if you use one."

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Last modified: August 06, 2011