A Roundy-Round Question

[davefoxx]

I know that the bus wires on a DCC layout should not be connected into a loop, even if the layout is a roundy-round.  The question then becomes should the track loop also have a break?  I don't plan on dividing my small layout into more than one block (excluding the reversing section), but should I at least cut a gap across both rails somewhere in the loop?  It seems to run fine now, and I certainly have never cut gaps on previous roundy-round layouts.

Thoughts?

DFF

[peteski]

I wouldn't worry about your small loop.  It is not that critical on small scale.   But if you are worried, cutting a gap will not hurt anything either and it might give you a piece of mind.

[davefoxx]

Thanks for the reply, Pete.  But, does it really even make a difference?  Please excuse my ignorance in electronics, since I'll probably use the wrong terms, but, let's say I cut a gap in the rails in one spot on the loop.  It seems to me that a locomotive crossing that gap, for a brief moment, is getting hit with the DCC signal from both sides that may not be in the same phase, i.e., the DCC signal on those two separate pieces of rails are coming from different parts of the DCC bus.  Wouldn't that actually be more of a problem?  I haven't had a problem without these gaps before, so is this really even a issue?  Maybe, as you pointed out, the small size of my typical layout makes this a non-issue.

Thanks,
DFF

[peteski]

Thanks for the reply, Pete.  But, does it really even make a difference?  Please excuse my ignorance in electronics, since I'll probably use the wrong terms, but, let's say I cut a gap in the rails in one spot on the loop.  It seems to me that a locomotive crossing that gap, for a brief moment, is getting hit with the DCC signal from both sides that may not be in the same phase, i.e., the DCC signal on those two separate pieces of rails are coming from different parts of the DCC bus.  Wouldn't that actually be more of a problem?  I haven't had a problem without these gaps before, so is this really even a issue?  Maybe, as you pointed out, the small size of my typical layout makes this a non-issue.

Thanks,
DFF

No, it won't make a difference on a small loop (which is  only several feet in circumference).  The phase will be the same anyways.  Actually even on large loops the phase must be the same (or else there would be equivalent of a short).

Here is a good explanation I found in one of the posts in this thread.

No, you shouldn't form a bus loop for a DCC system.  For a DC system, it doesn't matter.

On DC, the voltage rises and falls all over the layout at the same time.  I forget, though, if "DC" is true DC, or if it's actually rectified 60 Hz AC.  Anyone know?  In any case, in terms of propagation speed along the wire, 60 Hz is very slow.

DCC is what's called a "modulated square wave."  The voltage goes up and down much faster, and the way that it goes up and down is adjusted by the command station to send signals to the decoders.  If you make a loop, these square wave patterns will collide at the end, and they will, in all likelihood, be slightly out of phase.  The net result will be to "muddy" the waveform pattern, and make it just slightly harder for the decoder to figure out what's going on.

For most layouts, this slight degradation of "coherence" of the DCC signal will not be noticed.  The longer the loop, though, the more problems you're likely to see.

To add a bit more to that explanation, an electrical bus has resistance, inductance and capacitance. A combination of those properties causes delays to the electric waves traveling over that bus. That delay causes the undesired "mudiness" of the DCC signal as explained above.

[tehachapifan]

Glad this post came up as I'm planning on converting one or both tracks on my mainline to DCC at some point and they run in a rather large, continuous, bowl-of spaghetti-type loop with even a helix in there. I already converted a much smaller industrial branchline loop that already happened to have a couple insulated gaps in it for electrofrog turnouts, so I haven't had any problems. The mainline has no gaps...no, I never got around setting up power districts or isolated blocks...so I could've easily run into some problems with the conversion to DCC I suppose.

[peteski]

Glad this post came up as I'm planning on converting one or both tracks on my mainline to DCC at some point and they run in a rather large, continuous, bowl-of spaghetti-type loop with even a helix in there. I already converted a much smaller industrial branchline loop that already happened to have a couple insulated gaps in it for electrofrog turnouts, so I haven't had any problems. The mainline has no gaps...no, I never got around setting up power districts or isolated blocks...so I could've easily run into some problems with the conversion to DCC I suppose.

I doubt it. Unless you have club-sized layout (hundreds of feet of track) then I wouldn't worry about it. When the DCC bus has long runs, the way it is laid out (not just  the loops) can also affect the DCC signal. There are ways to deal with that (twisting or even separating the wires in the bus, or installing snubbers).

[tehachapifan]

Thanks, Peteski. Good to know.