Why use an bi-polar signal instead of DC with a superimposed signal?
There are a number of advantages to using a bi-polar signal: – The signal is the power, instead of just being superimposed on the power. This means that if you can get power to a locomotive, you can control it. Wiring loops and resistive loss, which can cause problems in carrier systems, do not cause problems with this technique. • The track stays cleaner, because there is no polarized electro-plating action as there is with DC systems. • The bi-polar signal simplifies the design as reversing the locomotive on the track has no effect on how it sees the signal. • It is possible to control an unmodified locomotive – see the section on compatibility for more details. Q: The standard implies that the track voltage can range from +/- 7 to +/- 20 volts. Is this how speed and direction are controlled? A: No. During operation, the voltage provided by the command station does not vary. The digital decoder within the locomotive controls speed and direction by varying the amount of power provided
