# Question



## mopac (Feb 24, 2011)

We have heard that bus wires of 30 feet or more can set up harmonics and distort the signal.
Or something like that. Lets say I run my bus wires 20 feet to the right of command station
and 20 feet to the left of command station. Here is the question. Is that 40 feet bus or is that
two 20 feet bus. The wires are connected at the command station.


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## higgsbosonman (Nov 17, 2014)

We have bus wires running under our club layout that are at least fifty feet long. As far as I know, this doesn't cause too much of a problem to the DCC signals, although the voltage drop for a fifty foot run is measurable unless you're using something like ten or maybe twelve gauge wire for the bus. As for whether the length of your run is 20 feet or 40 feet, I would say it is probably 20 feet because the two wires are in parallel.

The only other thing I could think of that would cause a problem for long runs is interference from stuff like (powerful/unshielded) radio equipment adding noise to the signals in the wires, or having a 120hz signal introduced because of the bus wire being close to the wires in the walls.


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## johnfl68 (Feb 1, 2015)

Mopac:

According to Allan Gartner's Wiring for DCC, it looks like that would be 2-20' busses:

http://www.wiringfordcc.com/track_2.htm#problem_excess_how_to

If you haven't already read through his pages, you may want to. Lots of good information to be found.

Twisting the bus pairs may also help with noise in the DCC Buss.

John


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## gregc (Apr 25, 2015)

mopac said:


> We have heard that bus wires of 30 feet or more can set up harmonics and distort the signal.


a signal on a transmission line reflects at the end of the line and travels in the opposite direction. This can cause standing waves when the signal wavelengths are smaller than the transmission line length. The wavelength of a 100 MHz signal is 3 meter or ~9ft. Standing waves causes signal suppression at different locations along the transmission path.

While the DCC frequency is not constant, it is less than 20 kHz. and not likely to cause standing waves.

The phone company learned that twisting pairs of wires can drastically reduce noise. phone lines can stretch for 2 miles.


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## tr1 (Mar 9, 2013)

*Long Wires 30'(+)*

wires longer than 30 ft. I read, (snubber's) come into play here.An R/C circuit.(resistive capacitive).I read that this circuit absorbs the high current levels (spikes)
which reduces reflections(additional noise).Up to an over 30' snubber's are recommended
Check out Mark Curries web sight. It has helpful recommendations. Regards,tr1


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## tr1 (Mar 9, 2013)

*Twist and Shout!*

I've also read, recently that, twisting long runs helps in reducing noise through cancelation of
signals. I'm not an engineer. Mark curries web sight has the info your looking for. Good luck!
Regards,tr1


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## DonR (Oct 18, 2012)

Tr1

Alan Garttner is one of the top brains in the DCC world. But the
technical advice in his writings are more for the very large layouts.

For the typical modellers layout, there is little need
for the techniques you have read about. If you are still building
or planning your layout then twisting the buss wires would be NICE. If you
have them already installed, but not twisted, that's fine. Most 
DCC layout buss wires are not twisted and most operate
just fine. The buss wires on my Room size DCC layout are not
twisted and I have no operating problems and there is no interference with
Radio or TV reception.

Don


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## vikramgoel (Mar 2, 2015)

I agree with Don, I have a room size DCC layout and I have runs of over 28 feet with un-twisted wire pairs and see no loss of signal.
Voltage can also be controlled by running a separate bus to power switches and stationery decorders using a small boster like the one from Tam Valley Depot http://www.tamvalleydepot.com/products/dccbooster.html

This works great and keeps power up for the entire layout.

Regards,

Vik.


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## tr1 (Mar 9, 2013)

*twisted pair*

thanks for the clarification on twist or not to twist.tr1


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