The MRC A/R instruction sheet shows a typical reversing loop. We use both MRC and Digitrax A/R modules on the layout. Installation is similar and they both work well.
One of the man advantages of DCC is the simplifying of the electrical wiring and components needed for operating a model railroad. The operation can be more "prototypical" (realistic) because multiple trains can be run anywhere on the layout and in any direction at the same time (As long as they don't try to occupy the same space). This means that it is easy to run "helper" engines and multiple-unit diesel consists (MU) from one throttle...or multiple throttles as in the case with real steam helpers.
Another situation that is simplified with DCC is the "reversing loop" or reversing section. This can be a loop or a wye or a turntable. All of these are somewhat problematic with conventional DC control. The reason is the "loop" turns back on itself and the "right" rail encounters the "left" rail causing a short. That short will also happen in DCC if precautions are not taken.
The solution is simple. The reversing loop or section is isolated by insulated gaps, as it would be in DC, and a DCC Auto-reversing module is used to power the loop or section (Wye or turntable). The A/R module will sense a short instantly and change the phase in the loop to match the phase in the "main line".
An interesting fact about a DCC "decoder", the little computer that controls each locomotive, is that the phase ("polarity" is sometimes used but the current is actually alternating in DCC) can change but the decoder will compensate and the loco will continue to move in the same direction. With DC the loco would, of course, reverse direction.
This auto-reversing is "transparent" to the operator and trains can traverse reversing sections without any intervention by the operator.
The track plan below shows the location of the three reversing sections on the SJSRR layout.
