DCC Bus wiring - to twist or not?

[C855B]

As mentioned, I twist. All of the "no problems" anecdotes don't trump my EE schooling. Pete is right, though - I have very long bus runs, 60-80 feet in a couple of cases, especially between the command station and peripheral boosters. Gotta do the twist. Short runs? Unlikely to see the difference, so carry on.

But "snubbers"? That's got to be some manner of fake science propagated by wannabe electrical engineers. "Snubbers" are fine on sine-wave AC, but DCC is a square wave digital signal, and what snubbers do is round-off the waveform. I've seen the difference on an oscilloscope, and in my book the terminators/end-of-run filters soften the waveform and may add to signal loss. In high-noise environments ("noise" being crap on the DCC signal), "snubbers" may attenuate the noise enough to improve signal reliability, but in, say, a home layout setting it is my opinion they do more potential harm than good to signal fidelity.

[John]

Yet, there is lots  of "helpful information" from the "experts" sprinkled all over the Internet.

These are my go to sources

https://wiringfordcc.com/

https://sites.google.com/site/markgurries/

[Bill H]

John:
Interesting, both of your go-to sources suggest twisting the bus wires. Perhaps that is somehow related to longer bus wire runs. Thoughts?

Kind regards,
Bill

[Bill H]

We also don't know any details about your layout and its future DCC bus.  Will it be a a simple straight bus, or will it have multiple branches?  Where will it be fed by a DCC booster? While N scale locos require fraction of the amperage of larger scales, having many feeders to the track is IMO good idea.

Peteski;
Pending the finishing of my basement, I only have the first module built, but I expect the basement construction will be finished in the next 30-45 days. I am modeling the B&O Toledo Division Second Sub in 1949 ish. Anyway, the current layout is a single level, generally single track with appropriate passing sidings, 154 feet mainline run, lots of operations work. 14 track staging yard, early transition with some steam and AB F7s. All with sound.  So far I am wiring with a #12 stranded straight bus following the mainline, solid #22 drops at least every 2 feet, with all track having drops without exception. #14 wires in the detection areas to BDL168s. Signals are powered by SE8cs. Digitrax 240 command station, two boosters, and most of the districts protected by PM42s. Currently JMRI but I am studying CATS. All the mainline turnouts are powered by Tortoises, the rest by slide switches that are connected to the throwbars by piano wires and move the throwbars and power the frogs. Everything is ME code 40. All the turnouts and crossovers are hand laid.

Hope this helps explain a bit better.

Kind regards,
Bill

[John]

John:
Interesting, both of your go-to sources suggest twisting the bus wires. Perhaps that is somehow related to longer bus wire runs. Thoughts?

Kind regards,
Bill

Bill -- I think for a large layout that is probably a good idea .. my main bus wires are qusi twisted because they go through the same hole in the benchwork and I ran them at the same time, but I didn't go to any great trouble to do it that way ..  the long side of my room is about 30 feet .. I did put snubbers at the end of each run ..  I;m not an EE, but both of those folks know more about this than I do ..

[peteski]

These are my go to sources

https://wiringfordcc.com/
https://sites.google.com/site/markgurries/

Mark and the other site is fairly trustworthy. But yet, lust like with doctors, there can be multiple differing recommndations out there.  There are still personal choices (even thought electronics is supposedly an exact science).

[peteski]

As mentioned, I twist. All of the "no problems" anecdotes don't trump my EE schooling. Pete is right, though - I have very long bus runs, 60-80 feet in a couple of cases, especially between the command station and peripheral boosters. Gotta do the twist. Short runs? Unlikely to see the difference, so carry on.

But "snubbers"? That's got to be some manner of fake science propagated by wannabe electrical engineers. "Snubbers" are fine on sine-wave AC, but DCC is a square wave digital signal, and what snubbers do is round-off the waveform. I've seen the difference on an oscilloscope, and in my book the terminators/end-of-run filters soften the waveform and may add to signal loss. In high-noise environments ("noise" being crap on the DCC signal), "snubbers" may attenuate the noise enough to improve signal reliability, but in, say, a home layout setting it is my opinion they do more potential harm than good to signal fidelity.

As I mentioned in the past, I'm not an RF engineer, and my electronic theory education is 40 years behind me.  But I know that twisting the wires will increase the bus' capacitance, so it will round off the sharp edges and soften any high-frequency ringing.

I also doubt that any external sources or electromagnetic radiation would be able to negatively affect the high power (voltage and amperage) DCC signal. Well, unless maybe you are running a MIG welder couple of feet away from the bus.   

I have not used DCC bus snubbers, but some DCC manufacturers (NCE?) offer those for sale, so that makes me think those are legitimate fix for some DCC bus issues.  And yes, those are just a type of RC filter.

[peteski]

Peteski;
Pending the finishing of my basement, I only have the first module built, but I expect the basement construction will be finished in the next 30-45 days. I am modeling the B&O Toledo Division Second Sub in 1949 ish. Anyway, the current layout is a single level, generally single track with appropriate passing sidings, 154 feet mainline run, lots of operations work. 14 track staging yard, early transition with some steam and AB F7s. All with sound.  So far I am wiring with a #12 stranded straight bus following the mainline, solid #22 drops at least every 2 feet, with all track having drops without exception. #14 wires in the detection areas to BDL168s. Signals are powered by SE8cs. Digitrax 240 command station, two boosters, and most of the districts protected by PM42s. Currently JMRI but I am studying CATS. All the mainline turnouts are powered by Tortoises, the rest by slide switches that are connected to the throwbars by piano wires and move the throwbars and power the frogs. Everything is ME code 40. All the turnouts and crossovers are hand laid.

Hope this helps explain a bit better.

Kind regards,
Bill

Thanks Bill.  To  be honest, I think you will be ok with a straight bus, but if it will make you feel better, twist it.  And if possible design it so there are no branches like "T" or "Y" topology.

[John]

As mentioned, I twist. All of the "no problems" anecdotes don't trump my EE schooling. Pete is right, though - I have very long bus runs, 60-80 feet in a couple of cases, especially between the command station and peripheral boosters. Gotta do the twist. Short runs? Unlikely to see the difference, so carry on.

But "snubbers"? That's got to be some manner of fake science propagated by wannabe electrical engineers. "Snubbers" are fine on sine-wave AC, but DCC is a square wave digital signal, and what snubbers do is round-off the waveform. I've seen the difference on an oscilloscope, and in my book the terminators/end-of-run filters soften the waveform and may add to signal loss. In high-noise environments ("noise" being crap on the DCC signal), "snubbers" may attenuate the noise enough to improve signal reliability, but in, say, a home layout setting it is my opinion they do more potential harm than good to signal fidelity.

@C855B @peteski Take a look at this ..  start about minute 8

[rodsup9000]

 I also twist mine, as 3 of them are in the 65' to 80' range. I read somewhere several years ago (don't remember where) that buses longer than about 40' benefits the most.

 Also in my CVP's "Easy DCC" orange bible (large book that was included with the set), it says to keep the bus under 100'. I don't know if that is only for Easy DCC or DCC in general.

[Bill H]

Peteski:
By straight bus, I meant topology, not Chubby Checker or not...

Kind regards,
Bill

[garethashenden]

I'm no electrical engineer, but I did talk to one about this a while ago. His conclusion was that a light twist was useful, but a tight twist was more likely to do mechanical damage to the wires than help the signal. His recommendation was either 2 or 4 twists per meter/yard of wire.

[C855B]

@C855B @peteski Take a look at this ..  start about minute 8

There's something weird going on there, John. Looks to me like an asymmetrical reactive load on the bus. If it was a balanced network, the spikes he's calling out would be even-ish top and bottom. You're eventually going to make me dig out my o'scope (under 2" of dust, it's been so long since I've used it), but not this week due to travel and prep thereof.

[peteski]

You're eventually going to make me dig out my o'scope (under 2" of dust, it's been so long since I've used it), but not this week due to travel and prep thereof.

I was also surprised to see those asymmetrical spikes.  Then I was hoping that he would show what the signal looked like after installing a snubber.
I will be curious what you see on the scope.

[John]

You're eventually going to make me dig out my o'scope (under 2" of dust, it's been so long since I've used it), but not this week due to travel and prep thereof.