Twisted Wiring & DCC Background

1) Part of the confusion is that many people do not understand the problem.  Clearly this is an Electrical Engineering topic.  However, there is little desire to make this a big topic within DCC only because in most cases, you do not need to deal with this.

2) This whole topic, twisting and Bus termination/Filter has been on the "Wiring for DCC" website for years and I have been talking about it much longer.  As I have said for years: 

a) if it ain't broke, don't fix it.  
b) Only twist wire when you install new wiring.  The priority should be given to long bus runs.  
c) DCC signaling techniques have been designed to be tolerant of this type of noise from day one minimizing you need to be concerned about all this.

3) Another issue is people falsely limit their thinking of the problem to a simple Yes/No answer.  The approach of treating it like it's a disease, you got it or you don't, does not apply.  When people say I do not observe a problem does not mean they do not have a problem.  They just do not know about the problem or know what the signs of the problems are.  Ignorance is bliss.  The truth is the noise is there but by far for most layouts, it is just not strong enough to be a concern.  This is what is called an "Analog Problem" where things are shades of gray.  Not simple black and white.

4) Another reason for confusion is that DCC is an AC signal.  Not DC like you old MRC powerPack puts out.  The only physics that you need to be worried about with wires when working with DC is what is called DC resistance.  Most people drop the term DC from the resistance term because until now, there was little concern for things like AC resistance or Impedance.  DC is DC.  Not AC.  Now some of you may say what about pulse power.  Yes that is a form of AC mixed with DC.  But the fundamental frequencies involved, 40 to 60 Hz, is so low that again the AC resistance is not an issue.  Life with DC trains is simple and it is natural for people to keep thinking that it is true for DCC.

5) The signs of DCC problems are not always easy to spot without a tool such as an oscilloscope. Something most people do not have yet alone know how to use.  That is NOT a put down.  Not everyone is an Electrical Engineer and thus can think like one.  That's OK.  This hobby is so cool because it involves so many degrees of talents and skills.  I would never want to say that to enjoy DCC requires an Electrical Degree or experience nor would any DCC manufacture.  This is why they will never mandate twisting the bus wires or installing a terminator/filter.  None the less, there are some electrical issues that can rear there ugly head from time to time which is why we try to come up with suggestions to help guide people when dealing with such issues as they are identified.  It is the laws of physics and I did not make the rules but people like me know how to deal with them.

6) Twisting the wires together (twisted pair) addresses all of the following issues:

Radio interference or EMI (Electro-Magnetic-Interference) control.
Controlled Bus impedance
Higher Speed Bus transmissions.
Shielding improvements
Voltage Spike reduction
Inductance reduction
Crosstalk reduction
Magnetic Field Control.
Signal Waveform Fidelity improvements.
Noise Rejection improvements.
Noise Sensitivity reduction.
Magnetic coupling reduction.

The specific term associated with twisted pair wiring DEPENDS on the GOALS for doing the twisting of the wires in the first place.  Hence what people think are conflicting terms are in fact the same terms just tailored to the problem at hand.  As is often the case, there is one key technical issue that is the driving goal behind twisting.  But there are all the other remaining benefits you get for free that come with twisting like it or not!

7) Regardless of the reason in #6 above, BEHIND THEM ALL is the same simple physics issues.