Since I've decided to go with the NCE Powercab, I was reading the online manual. There is something I read that I don't quite understand, and don't even know if it would pertain to me? On page 13 it says: "If you are going to have long runs of cab bus cabling along the front of the layout you should run the track bus wires nearer the rear to prevent potential “crosstalk”between the track signal and the cab bus." Can someone explain that to me, like I'm a 2 year old (because sometimes I am) My layout is going to be roughly 38x94 and I don't have a track plan as of yet. I'm finishing up my benchwork this week. Thanks, Bill H
Crosstalk I'm not an expert, and I don't even know if I have the terminology right, but I first ran into this concept several years ago when I was wiring my house. My brother in-law suggested that I keep the phone, data and cable wiring runs seperate to avoid crosstalk. I had no idea what he was talking about, but followed his advice. I now know that when you use electrical wires as a means of signalling (like telephone, cable, DCC bus) you should keep the wires seperated to prevent the signal carried on one wire interfering with the signal carried on another wire. This is "crosstalk". http://en.wikipedia.org/wiki/Crosstalk The system you are using employs two seperate signal systems. The track signal (or DCC signal or track bus) which carries DCC commands to the DCC devices connected to the track (decoders, switch decoders). The cab bus is a secondary signal system that carries messages between DCC devices independant of the track bus. These are often status messages, which indicate the state of certain devices. The manual is stating that you should avoid running these wires in close proximity to each other. From what I understand, you should try to avoid running the wires paralell to each other in close proximity.
gpa is correct, and with a layout the size of your's, you shouldn't have to worry. Just don't take your power wires going to your track (track bus) and twist them together or run them right together with your NCE cab bus wires. On my layout, I have the Digitrax Loconet wires running within 2-3" of my track power wires for about 6' and I have no problems. -Mike
Just keep your bus lines (track power) separated from NCE cab bus lines. On the JJJ&E each set of lines runs in a different parallel channel. Have fun...
The DCC track bus carries a higher current signal that can interfere with the lower power signals on parallel Expressnet or LocoNet busses. This is only an issue if the two are in close proximity and parallel for a significant stretch. Keep 'em 6" apart and cross at an angle and you'll be fine. If you already have parallel runs, see if there are any problems before ripping it all out and starting over. You may be OK anyway.
Hey guys! I just got home and tried to make sense of this but it's been one heck of a day and I'm spent. When I get up and my heads clear I'll re-read and I'm sure it will make sense to me. Just wanted to thank you all for the help! Bill H
A transformer works by transferring an AC signal between two coils of wire in close proximity. If you unwind the coils of a transformer so the wires from the coils are stretched out close alongside each other it will still work (less eficiently for most common types as the iron core would now be missing, but still working). If you now move the wires apart the efficiency will drop as the distance increases, so the amount of signal transferred reduces. The converse is also true. If you have parallel wires, one of which has an AC current in it, that signal will be radiated across to the other. The closer they are, the more it will happen. In audio circuits this can result in sounds, like talking, appearing in places they aren't meant to. Hence the term crosstalk. In digital circuits the effect is that signals from one circuit may get across to another and confuse or jam it. Twisted pair cables and shielding/screening are a couple of ways the effects are reduced, which is why it is important to use the cable type specified for the application - all wire is not equal
While the 6-wire Digitrax cable is certainly easy to use (to crimp on plugs), it is flat and not twisted. I was surprised they didn't adopt easily available and twisted-pair ethernet cable. The latter is a little more impervious to cross-talk. I have medium size home layout in the basement and so I have not had any problems no matter how I have routed the LocoNet. I just this evening changed the location of my main command station, so I have re-routed some of the LocoNet cables as a result of this thread and other reading. ... JD
AJ Ireland (Digitrax owner) recommends flat 6 wire cable for loconet. At the DCE in June, he mentioned that twisted pairs could actually cause more trouble then help. I believe it has something to do with which wires get paired up.
Others have covered the reality well, but no one has told you exactly why. Basic electricity. A current flowing through a conductor creates a magnetic field. Collapsing a magnetic field around a conductor creates a current. So the pulses going through one wire - binary, so even a small number like a locomotive address of 6840 is 11010110111000. The ones will be voltage, for microseconds. If the neighboring wire induces even a tiny voltage to make it read 11110110111000, that gives a value of 15800. Not even close, and computers only recognize exact. Really sensitive digital signals on cars use shielded wires even - a foil wrap that has a ground strap on it. Now you know more than you need to know, just keep them apart. It may be a tiny layout now, but what if it grows in the future? What if DCC gets more advanced? Look at the difference in computer technology just in the last 5 years! Wouldn't you hate to have to rip it all out later?
