Telco Using Ethernet/CAT Cable for Cab Bus/Loconet

I would only explore this topic if you are:

1) building a new layout and want to install a better cab bus using common inexpensive ethernet cables. 

2) having problems with the cab bus itself when the trains run.  Poor throttle control issues.

Electrical Noise cab bus problems can be addressed buy using ethernet cables which offer many communication benefits such as eliminate crosstalk with other DCC wiring cables.  Think of a "poor mans" shielded Cab Bus cable. 

If you current cab bus is working just fine, there is NO reason to go out and replace the wiring.



The topics in this section are:

1) The CrossTalk Problem
2) How does this relate to DCC?
3) The Long Cable Run
4) Ethernet Cable Backround Information
5) Advantages and Disadvantages of each type of cable.
6) The Two Ethernet Cable Conversion Options:
    6A) NCE's RJ45 UTP Cab/Throttle Panel System using standard RJ45 cables.
    6B) Replacing 6-Conductor Telco flat Cable with Cat cable.
7) NCE 6 Conductor to CAT Cable Signal Pair Strategy  
8) Digitrax 6 Conductor to CAT Cable Signal Pair Strategy 


1) The CrossTalk Problem

In electronics crosstalk (XT) is any phenomenon by which a signals transmitted on one circuit or channel of a cable or wire creates an undesired effect in another cable or wire. Crosstalk is usually caused by undesired capacitive, inductive or conductive coupling from one circuit to the another.  In telephone industry, crosstalk is often described as pieces of speech or tones leaking from other people's connections.  This was most apparent when the telephone line ran for miles and miles.  How would you like other people hear your phone conversations, intentional or not, when you have different phone numbers?   One normally expect to have both a private and high quality voice conversation when using the phone.


2) How does this relate to DCC?

On our layout, we have cables and/or wires that carry the DCC track power from the booster to the track.  The wires must carry all the noise and power spikes (voltage and current) that occur naturally when running moving engines on rails.   Why?  The connection via the metal wheel used for electrical pickup between the engine and the rails is intermittent.   Uneven rail surfaces can cause the wheel to bounce and lose contact for a brief split second.   The more pickup wheels the engine has the better but even then it still not perfect when you factor in dirty track and wheels.  You have the short circuit problem which can be momentary through a switch or steady state due to a derailment.  The point is that these wires are very electrically noisy.

In contrast, the cab/throttle bus carry information between the throttle/cab and the command station.  Reliable communication is paramount if one is to have complete control of the trains the engineer is running. The common "modular telco cable/wire" system is designed to be low cost.  But to reach the low cost goal, it comes with the compromise that is must be restricted to being a short distances cable run such such as found between the phone jack in the room to the actual phone itself.


3) The Long Cable Run

As noted in the long phone line crosstalk issue, it was the long run of multiple wires bundled together in a single large cable that created this problem.  For a given length of wire(s), the higher the speed the signal waveform gets the more crosstalk you get between the wires.  Granted that we do not have miles of wires in our layout, but the problem happens none the less especially when we use high speed signal such as found in digital communication.  These type of high speed Digital signal waveforms are found on the DCC signal on both the track and on the cab/throttle bus which means it is much easier to get crosstalk problems between the two.  Furthermore, on large layouts, there we run wires over much longer distances than one would find on a small home layout.   Together the digital high speed and long bus runs greatly increases the opportunity for the cables to cross-talk to each other.   


4) Ethernet Cable Backround Information

The common flat "Telephone cable" is a "communication cable".   Communication cable are cables that have features that help with quality signal transmission over a simple wire cable.  However flat cable was never intended for long distance runs of signals including telephone.  It was intended for indoor use and to go short distances between the telephone wall jack and the actual telephone in the room.  An alternative to using flat telephone cable is to use Ethernet cable instead. 

Ethernet cable is constructed of 8 wires that form 4 twisted pairs.  Each twisted pair consist of only two wires.   The twisted pairs are not twisted together with any other twisted pair.  All 4 twisted pairs share a common outer case that hold them together.  Each twisted pair have unique colors to help identify which of the 4 twisted pair you have.  Each twisted pair has a modification of the color pattern to help you identify which wire you have within the pair.  All 4 pairs are identical in contstruction, design and performance.  So they are interchangeable with each other.

Ethernet cable goes buy names as CAT3, CAT5, CAT5E and CAT6.  Reading from left to right, each of these cables designations allows for higher and higher speeds of communication.  The cost typically goes up too.  CAT stands for CATegory in reference to the ETHERNET standard.  For our purpose, any one of these category cables will work. 

Ethernet cable is available at most big hardware chain stores and computer stores.  It comes in a box for long cable runs or in pre-made lengths something like 8, 16, 25, 50 or 100FT.    


5) Advantages and Disadvantages of each type of cable.

Ethernet Cable advantages relative to Flat Telco Cable

1) Larger wire gauge mean less voltage drop in the cable for a given length of cable.

2) Twisted signal lines means:
     2a) High quality signal integrity.
     2b) High noise rejection both in pickup and transmission.

Ethernet Cable disadvantages relative to Flat Telco Cable

1) It will requires you to make a custom cable.  There are no pre-made cables with the right connectors installed available.   Note: Having the right tools is critical to making a reliable cable.  For more information on how to make a reliable cables go here: Telco Making cables

2) The cable will cost a little more than the Flat cable on a per foot bases.  However it is a lot cheaper than using other multi-conductor communication cable options.


6) Ethernet Cable Conversion Options

There are two ways to integrate Ethernet Cable to be your cab bus /loconet bus.

1) Install NCE's new RJ45 UTP Throttle/Cab panels.  Plug and Play method.

2) Replace the existing 6-Conductor Cable.  This is low cost Do It Yourself (DIY) method.

Each method is discussed below.


6A) NCE's RJ45 UTP Cab/Throttle Panel System using standard RJ45 cables.


NCE has recently introduced RJ45 UTP Throttle Panels and adapters that allow one to use Standard low cost Ethernet Cables for cab bus connections between panels.   You can find complete information on this CAT (RJ45) wiring system here:NCE RJ45 Cab Panels

  






6B) Replacing 6-Conductor Telco flat Cable with Cat cable

In this section, we are replacing the 6 conductor flat telco cable with an Ethernet cable.  NCE, Lenz and Digitrax cab/throttle buses are all implement using a 6 conductor cable.    Hence on wire pair of the Cat cable will not be used.

1) CRITICAL INFORMATION:  Do not use the same RJ Telco Plugs you use on the flat cable on Cat Cable.   
WHY?  They are designed for STRANDED WIRE as found in the flat cable.  CAT CABLE USES SOLID WIRE.  Using the wrong type of plug will lead to connection failure inside the plug.  I found out the hard way!!!  The correct RJ jack to use for Ethernet Cable are found at DigiKey. Use this link to order the correct connectors.


2) What ever signal pair you assign to a given twisted pair in the cable, WRITE IT DOWN and use it as your wiring standard.  Save this document so you can refer to it again as needed.

3) If you are buying a pre-made Ethernet cable length, it will come with the incorrect 8 conductor installed on both ends.  Jut cut those plugs off!!

Here is a link to a video on YouTube that shows you how to do to crimp a Category Cable onto at 6P6C RJ12 plug:  
However you do NOT follow the discussed USOC color pair code.  That code is for computers.  In the sections below, your are shown what color code you need for DCC. 


7) NCE 6 Conductor to CAT Cable Signal Pair Strategy   

The key in minimizing crosstalk and keeping the signal clean it to pair up the signals in the flat telco cable with it complement in the same cable.  The noise sensitive line is the RS485.  Hence the RS485+ line has a RS485- line pair up to each other.  The +12V line has a corresponding GND line are paired up to reduce noise.  Below is the suggested plan:

NCE


NCE 
Signal
Name
 NOTES
RJ12
Pin
#
RJ12
Flat Cable
Color
 Category Cable Pair Color
Pair
#
Reserved2White Orange 1
GND 1Black Green2
RS485+ 13RedBlue3
RS485- 14GreenWhite/Blue3
+12V 15Yellow White/Green2
Reserved 26Blue White/Orange1


Notes:

1) CAB Bus:  Today, you only need 4 conductors between the command station and any cab or RB02.   However, you will have a more rugged and flexible (options) cable if you make it for 6 conductors just like the how the normal flat cab bus cable is made.

2) NCE Radio Repeater Bus:  Requires 6 conductors.  Hence another reason to just make 6 conductor cables!



8) Digitrax 6 Conductor to CAT Cable Signal Pair Strategy 

The key in minimizing crosstalk and keeping the signal clean it to pair up the signals in the flat telco cable with it complement in the same cable.  Each GND signal pairs up with a Loconet Line. The RailSync+ line has a RailSync- line to go with it.  Below is a suggested plan:


Digitrax
Signal
Name
 NOTES
RJ12
Pin
#
RJ12
Flat Cable
Color
 Category Cable Pair Color
Pair
#
Rail Sync  White Orange 1
GND  
Black Green2
Loconet3RedWhite/Green2
Loconet 14GreenWhite/Blue3
GND  
5YellowBlue
Rail Sync 
6Blue White/Orange1


Notes:

1) The Loconet signal is not a differential signal.  The signal on Pin 3 is the same as on Pin 4.

Loconet with Twisted pair wiring (CAT5).

In the DB100+ manual on page 20, it says:

"You can also use regular 3 pair AT&T Internal Wiring solid conductor twisted pair wires. These actually have superior noise rejection due to their balanced twisted pair construction."

Recently (2012) it has been reported on the Digitrax DCC List that Digitrax now says you cannot use twisted wiring for the Loconet.  Why this was stated recently and being the opposite of what was stated before, I do not know.   The person reporting this did not state Digitrax's reason as to why this is now true but is apparently accepted it as gospel.  (See story below).  However, there is nothing on the Digitrax Knowledge Base that supports this Digitrax statement.  For all I know it was a recommendation intended for the person asking about it .

I cannot, from an electrical point of view, understand why twisted pair wiring will be a problem nor have I heard of a case on the Digitrax list where twisted pair wiring actually caused problems.  I only see positives and not negatives IF the cable wiring is done correctly.  The IF statement may be a clue to Digitrax's new position if in fact it is their new position.   I believe Digitrax issue is NOT the twisted pair wiring itself but Digitrax does not trust its customers to build the CUSTOM twisted pair wire cables correctly.   Specifically if you pair up the WRONG signals together, you will end up creating problems as opposed to solving them. 

Digitrax DCC List Story:  On the Digitrax List in 2012, there was a topic of a layout owner having a two-way radio (UR92) problem with his 2500 SqFt layout.  The layout had been using a well designed and installed twisted pair wiring for the Loconet for 8 years without any problems while using a one way radio system (UR91).  Then the layout owner upgraded to Digitrax's two way throttle radio system and experienced operating problems.  At the time a Digitrax list contributor argued that the layout owner must replace the twisted pair based Loconet cables with telco cables because of what Digitrax said so to him.  The layout owner protested but complied after upgrading the UR92 radio system with the latest (but still buggy) software that did not solve the problem.  Post rewiring, the layout owner still reported problems (slightly different ones) but felt the rewire did nothing to solve the radio problem and was a big waste of time, money and energy.  Time showed many other Digitrax layouts were reporting identical inconsistent and poor performing two-way experiences and they were using normal telco cables.   In the end it was a hard to find software bug.  The point of this story is that twisted pair wiring had nothing to do with the problem.  The layout owner is still upset and regretted listening to this person.