Re: Jmri interface


If you are using double insulated line cord designed for 110V then you don't have a safety issue.  The cable is safe in all circumstances.  The primary source of any noise that might have an effect on low level signals is actually coming from your DCC components.  If your system is legally compliant with FCC rules then there will not be anything on the AC wires that will mess with your low level signals (this may not be the case because enforcement is rare).   The ability of the AC signals to impart interference onto the low level signals is a function of proximity, how long the wires are in close proximity and whether the fields of the wires are aligned.  This is the reason that twisted wire is recommended and used CAT5 and other internet wires.  When you twist the wire the effect of alignment and proximity is essentially eliminated.

Your DCC track wiring is actually vastly more likely to effect adjacent low level signal wires than anything else.  This is because the track wiring is higher frequency, carrying significant currents and consists of more or less square wave signals.  The frequency content of a square wave is many times higher then the basic frequency of the signal.  The higher the frequency and the greater the power the more likely it is to couple to nearby cables.  A clean 60Hz signal won't get very far.   The audio noise we associate with 60Hz power is generally because of the fluorescent light fixtures connected to it.  The fluorescent load can broadcast high frequency noise that occurs at a 60Hz rate.  Hence we hear the 60Hz but not the much higher frequency noise that is broadcasting it into the air.

I hope I have kept the simple and concise enough to be understandable.  The mechanisms involved are very complex and are not at all easy to predict.  Small changes in the configuration of cables can have huge effects.

Ken Harstine
BSEE with 40 years of experience in various aspects of electronics including technician work early in my career and significant experience in getting new systems to comply with with FCC rules.

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