A question for the electrical engineers out there - or anyone who has experience with this:
Is there any advantage gained by twisting the feeeder wire pairs on a DCC layout? What about the bus wires? If there is, how much twist is good?
Twisted pair is a cheap and simple way to get some of the advantages of shielded cable.
Unless you have a really big layout, I don't see any need for it. Mine is an 18x18 foot single level (unless you count the subway) around the room layout and has no problems at all without twisting or shielding.
If you do choose to twist, the easiest way to do it is to pull the wire out straight and tight and put one end into the chuck of a cordless drill ...
Be advised that twisting will very substantially shorten the length.
Dave
Lackawanna Route of the Phoebe Snow
Jeff But it's a dry heat!
Twisting the buss wires would shield the dcc signal from posible effects from a powerful radio signal from say a telephone or even a key fob for unlocking your car. The HO scale module group that I belong to does not twist the buss wires and at one show a couple years ago there was nine layouts inside one building and we had all kinds of problems that day. Since then all new modules will have twisted buss lines. On another forum there had been a confirmed issue with a key fob from a Toyota that would operate the switch motors on a DCC layout that was not even wireless. All throttles are teathered.
So dont twist if you want but I will from now on. You dont need too many twists just three to seven per foot is plenty and dont forget to terminate the buss ends.
Pete
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It certainly doesn't hurt anything to twist if you want to do it as a precaution, but I would be more inclined to think that radio throttles from the other layouts, or at least the radio receivers on your layout, were the source of your interference troubles.
A radio signal, even from a key fob or a cell phone, is not strong enough to impose it's signal on the buss. It could, if it was very close, interfere BEFORE the booster, perhaps in the throttle wire or layout radio receiver. The booster would then amplify the interference. But the buss is AFTER the booster. It's signal would be so much stronger than any possible interference that false signals are unlikely.
locoi1sa wrote: ... and dont forget to terminate the buss ends. Pete
... and dont forget to terminate the buss ends.
Terminate, like into a load? How much resistance? Or could it just terminate into a pair of feeders?
I have to say I never bought the key fob story. No normal interference in going to mess with the bus, more likely the other way round, actually.
OK, here's the NCE manual, page 17 is of interest. They recommend twisting, 3 times per foot, it the bus its over 20 feet. I"ll maintain it shouldn't matter, but it won't hurt. Also on that page is a diagram of a "snubber" to terminate a long bus.
There has been a lot of discussion on the NCE user group on Yahoo, and though the official line is to twist, most are not. My layout is three deck, 36' by 28' with four power districts. the cab buss is split three ways, so it is not excessively long on any of the three. The power busses are 12 gauge twisted, they are about a foot from each other all the way around. They terminate at power strips.
My layout has been operating with NCE since 1999 with no issues in the buss department.
Bob
Yes, a long wire can act as an antenna, but a microvolt radio signal is not going to overpower a 14 volt track power signal. Signal people twist, or better yet use shielded cable when two different signals run close together for long distances. An example would be a long run of your speaker wires through a common conduit, or just side by side.
The Loconet or Railnet buss could be a different story, but that is not how your signal is getting to the trains. I suppose it could throw a switch. A really long lead to your hard wired throttle could do it if the signal was very close to it.
But, like I said, it won't hurt anything. If it makes you feel more secure, by all means twist it.
Along the same concern for inductive coupling, if your buss wire is too long, cut it. Don't coil it. It can inductively interfere with itself.
de N2MPU Jack
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Jay
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Its not so much the interference part of the twisting debate its keeping the digital signal clean and uncorrupted. It does not take much to dirty up the digital signal. Just round off a couple of those square waves and you just confused a decoder. Marcus on the NCE yahoo group has done quite a lot of research with the right equipment to come up with the best solution to head off potential problems before they occur. The track is not twisted as we all know but its not as long as the buss. There are joiners and gaps and power districs. Its the decoder and where its at on the track that determines where the end is and how far the current travels. Keeping the feeders as short as posible and a couple twists of the buss wires is a small price to pay for reliable operation.
I did not twist any of my wiring and I have 2 busses, that are 40+ feet long and one that is 58 feet, (all 12 gauge), I have many 20 gauge drops that are 2 to 3 feet long, also not twisted. Some of my blocks/districts are up to 60 feet. I have had zero problems in the year and a half since I switched from DC.
I think there is a tendency for some people to get rather anal about potential theoretical problems which often don't translate into the real world. In addition, as I understand it, the command stations send out multiple "packets" of info/commands so there is redundancy in the signal a decoder recieves just for this reason.
I think it's more important to keep the track buss, throttle buss and any other electrical lines separated by at least six inches and if you do have cross over lines do so at 90 degrees.
modelmaker51 wrote:...And who listens to AM radio anyway
WHats an AM radio? And can you use it in the PM?
-G .
Just my thoughts, ideas, opinions and experiences. Others may vary.
HO and N Scale.
After long and careful thought, they have convinced me. I have come to the conclusion that they are right. The aliens did it.