KB947: The Difference Among DCC Systems & DCC Companies

This article was last updated on June 29, 2011, 7:08 p.m. | Print Article | Leave Feedback


In response to questions about the differences among the DCC systems that are currently available from different companies, I offer the following comments & observations. You may have heard that all the systems are pretty much the same or you may have seen “comparison” charts in various DCC companies’ literature, in magazines or “analysis” on the Internet by “impartial observers.” Unfortunately, it is almost impossible to break down the system and company differences on a simple chart & the people who write the “impartial analysis” are usually not really impartial. As you read these comments, please keep in mind that I am extremely biased since I am, after all, the president of Digitrax.

When people ask me why they should buy Digitrax, the answer I give is very simple: “Digitrax costs less and does more.” Let’s go a little further and explain some of the differences that will be important to you when you decide on a DCC system.

Because of the way each company packages the various components needed to make up a DCC system, “comparison of features” charts have a hard time comparing “apples to apples.” The components needed for a DCC system are: a command station to generate the command signal, a booster to combine the command signal and power and put them on the track, a throttle to input your commands to the system & decoders to decode the signal and control the locos (& other accessories) & the control/cab bus or network to link the hardware together into a system. In addition, there are “basic” throttles, radio throttles, infrared throttles, computer interfaces, reversing units, connector panels & other devices that can be added to your DCC set.

Every system has a unique place in the DCC market. We encourage you to shop around and find the one that suits your layout and style of operation. You may find that you like components of one system better than those of another and you may find that a mix and match approach will work best for you. The DCC standard gives you that flexibility!

1. First lets talk about what you need to get started & how much it will cost (I have chosen to avoid naming any DCC companies other than Digitrax because I can’t be certain that my facts are correct. It is best for you to verify facts & figures directly with the other DCC companies before you make your purchasing decision).

All DCC system companies offer sets. Some offer only one set while others offer multiple sets. Digitrax believes that you should be able to begin your DCC journey at a level that is comfortable for you so we offer three sets, basic, advanced and premium. Each Digitrax set is expandable by adding system components to increase system features and capacity. We don’t think that one size fits all!

When comparing system prices among companies, be sure you are comparing apples with apples when you look at the components included in the starter set.

There are significant price differences among the systems. There are of course differences in system performance & capabilities as well.

2. The most significant, but by no means the most obvious, difference among the systems is in the system architecture. Even though this is transparent to the end user, this is where there is a really big difference among DCC systems.

The system architecture used by the DCC company you choose will affect your DCC system particularly in the future when you are ready to expand. Digitrax uses an open-ended system architecture that gives us a road map to the future for features that you want to add and for some features we haven’t even thought of yet!

We encourage you to learn the real differences among systems and look beyond simple, superficial “me too” product comparisons. All DCC systems have (and need) boosters, throttles, decoders and other system components. It is important to know that not all DCC systems have a well thought out plan for reliable, efficient communications today that includes future expandability and enhanced system performance down the road.

There is a big difference in the technology, implementation and philosophy of Digitrax LocoNet as compared to the strategies implemented by other DCC companies.

3. The most obvious superficial difference among the systems is the layout of the handheld keypad. Because there are so many features available with DCC, all of the keypads take some getting used to & it really boils down to what you like best.

Each company has a different throttle configuration. There are controls for speed, direction, functions, turnouts, consisting, programming, etc. on all DCC throttles.

Speed controls:

Knobs with Rotary Encoders are like non-stop potentiometers; there is no physical 0 position and no physical full speed position. This means that you have very fine speed control because the encoder rotates more than once from 0 to full speed. Encoder throttles can let you access any loco that is running on the layout at the actual speed it is running without needing to adjust the throttle position to the loco’s speed. Click encoders are used by Digitrax to make the knobs more useful.

Up and Down Buttons for increasing and decreasing speed are available on several different throttles. In some throttles you must choose whether to use the keys or the thumbwheel for speed control. Digitrax offers up and down arrows for speed control that can be operated at the same time as the rotary encoders for speed control on the DT400 series throttles.

Thumbwheels for speed control come in two varieties. The potentiometer type and the encoder type. Potentiometer type thumbwheels are somewhat restricted in their ability to take advantage of 128 speed step control because they are limited to a small diameter and about 3/4 turn, so the interface is just not sensitive enough for full resolution. There is a also a thumbwheel on some throttles that will reverse your loco if you continue to rotate it below the 0 speed position. This works fine if there is a “detent” to warn when direction is about to reverse, but can be confusing since going in the counterclockwise direction may not always result in a speed reduction.

Large traditional knobs for speed control are used on simple throttles by most DCC companies. These potentiometer knobs offer good control in 128-speed step mode. The problem has come up when you select a loco to run and the potentiometer has been left at full speed and the loco then takes off! Digitrax uses a safety reconnect feature on the Utility Throttles that prevents this from happening. If the speed of the loco on the layout does not match what the system thinks it should be the Utility throttles will prompt the user to change the position of the potentiometer so that you don’t get unexpected operation.

Slide controls for speed control. These are limited by the range of the slide and by the fact that the systems that use them are generally limited to 14 or 28 speed steps.

Key Pads, How Many Keys Do You Need?

DCC throttles have widely varying numbers of keys. Digitrax DT400 series throttles have 32 keys.

The Learning Curve

The bottom line is that no matter which throttle you choose, you will go through a learning process and once you are “over the hump” no throttle is significantly more difficult to use than any other. If you have visitors run your layout often, consider having simple traditional throttles available for them. Traditional throttles are simple for visitors to use. All DCC companies offer simple throttles for this purpose.

4. DCC companies use different plugs on their throttles and use different wiring schemes for their throttle bus or network.

You really don’t have to be too worried about the plug that’s on the end of the throttle. Choose the throttle you like best and as long as you have the right number of wires on your control bus or network, you can rewire the throttle connectors to suit yourself.

5. Another difference among the systems is how they handle analog operations.

Digitrax supports the operation of one analog address on a DCC layout & Digitrax decoders automatically convert to DC operation when placed on a DC system. This gives you the flexibility to convert your fleet to DCC over time because you can always run one DC loco on your Digitrax system. You can take your Digitrax decoder equipped locos to a friend’s DC layout and run them there too!

6. Multiple unit operation is handled differently by each system.

There are three methods of consisting available with DCC:

Basic Consisting where locos are simply programmed to run on a single address. All the engines must run in the same direction, unless “direction swap” is supported by both the decoder and command station. Adding and removing locos from a consist requires reprogramming of the locos. Digitrax Genesis II and most other basic systems use this method.

Advanced Consisting (often called Decoder Assisted Consisting) where the decoder has both its own address and a consist address. The decoder maintains the consist information internally. This method requires extended packet format or EPF decoders and cannot be used with baseline DCC decoders or with analog engines. Engines can be added and deleted and can be run in either direction. If an advanced consist is removed from the track and transported to another location, care must be taken to set up the locos in the exact orientation and state they were programmed for or you will get “shocking, horrifying results” when you try to run them at the new location! “Advanced Consisting” will not work with decoders that do not have this feature. All current production Digitrax starter sets beginning with Empire Builder II and Chief II Sets offer this method as well as Basic and Universal Consisting.

UniVersal Consisting where the command station keeps up with the consist information. This method allows all DCC decoders and an analog engine to be included in a consist. Engines can be added and deleted easily and can be run in either direction. The operator can control the lights & functions for each loco within a consist separately.

Digitrax Chief Series Starter sets beginning with Chief II offer all three methods with virtually no limit on the number of units in a consist. Digitrax Empire Builder Series starter sets begining with Empire Builder II also offer all three methods but are limited to 22 locos running at any time either as part of consists or as single units. Digitrax Zerphyr Series Starter Sets allow all three consisting methods.

A couple of other forms of consisting are available in some DCC systems. “Old style consisting” that is similar of UniVersal consisting is offered by some DCC companies but it is limited to 4 engines in any consist. Some DCC companies limit the number of locos that can be included in a consist no matter which method of consisting is used.

7. Programming Differences Among DCC Systems

There are several ways to program decoders with DCC systems:

Broadcast programming is done by having the command station send programming information to everything on the track. The disadvantage of this type of programming is that the command station can either send programming information or packets to run the layout. Both can’t be sent at the same time so consequently, you will have to shut down the layout to program decoders.

Separate programming outputs are available on some premium command stations. In this case, the command station has two outputs, one for packets for layout operation and another for programming packets (or other packets, too.) This means that the layout can continue to operate while programming is done on a separate programming track.

Operations mode programming is also available in some systems to allow for changing CV’s while an ops mode capable decoder is on the layout. This method directs programming information to a specific decoder address.

Digitrax Chief series Starter sets offer separate programming outputs and operations mode programming. They have the ability to run the programming track while mainline operations continue.

Digitrax Empire Builder series Starter sets offer broadcast programming and operations mode.

Most other DCC companies offer broadcast and operations mode programming. A few have separate programming outputs.

In general, DCC compatible decoders can be programmed from any DCC compatible command station. Programming compatibility problems do occur from time to time and for the most part, there are work-arounds available. These problems were caused because several different programming strategies have been allowed by the NMRA's "Recommended Practices" or RP’s and not all of the strategies are supported by all systems. The RP’s allow for paged mode, direct mode, physical register mode and operations mode. Digitrax uses paged or direct mode as the preferred programming methods. If you experience programming problems, contact the DCC company that produced the decoder you are using for assistance.

8. Throttle Response Curves, Low End Speed Control, Speed Step Resolution (14, 28, 128 or something in between?) and Speed Stabilization (Back EMF)

The throttle response curve is the relationship of the motor voltage to the speed step command sent by the command station. Because the DCC signal is digital, the throttle response curve has a defined number of discrete speed steps from 0 to full voltage. DCC companies and systems offer a wide variety of possibilities from basic 14-speed step operation through high-resolution 128-speed step control. What all this really means is how fine is your speed control, especially at the low end. 14-speed step operation is fairly coarse & 28-speed step operation is only a little better when compared with 128-speed step operation. Some decoders offer speed stabilization or back EMF control to help smooth out operation in the low end. This feature can be beneficial especially in N scale switching situations especially when the decoder can select how much of this effect to implement (scaleable speed stabilization). This feature is also used in decoders with less than 128 speed steps to smooth out the effects of 14 or 28 speed step operation. Speed stabilization is a decoder feature that can be used with any system. Many US modelers consider speed stabilization to be non-prototypical so in most cases, decoders allow you to disable this feature.

Only a few DCC companies don’t offer 128 speed step operation in both their decoders and command stations, today. Other DCC companies offer 128 speed steps in some decoders but not in all of their command stations. Some companies do not offer 128 speed steps at all. If fine speed control is important to you, it is worth checking on!

Note: The NMRA "standard" allows for decoders that are 14 speed steps to run on the same layout as decoders that are 128 speed steps. However, you may need to reprogram decoders and or your command station to be sure that these components will communicate with each other on your layout. For example, 14 or 28 speed steps decoders will run on a Digitrax command stations (128 speed steps) but you will have to follow the instructions and do a little extra work to make things run smoothly.

9. DCC Innovations

The DCC "Standard" provides a framework for interoperability without precluding company innovation in most cases. Since the DCC format does not cover anything beyond track level protocol between the command station and decoder, DCC companies are free to go above and beyond the standards to offer new features outside that realm. Most of these innovations fall outside DCC proper.

It was a real victory for DCC when Digitrax plug 'n play decoders were voted most innovative product of the year in 1997 by the readers of Model Railroader Magazine!

The following are some of the innovations created by the engineers from Digitrax and other DCC companies:

Digitrax: transponding, scaleable speed stabilization (adjustable BEMF), safe mode for throttles, duplex and simples radio control for DCC, simultaneous dual Radio/IR operation for tetherless operation, plug n’ play decoders for HO, solderless retrofit harness for Athearn loco installations, modular backbone wiring, automatic reversing boosters, decoders with onboard functions in addition to forward and reverse lighting, FX lighting features, UniVersal Consisting, 4 digit aliasing for 2 digit address decoders, analog mode disable for stopping blocks, 128 speed step control, encoders for fine speed resolution, dual throttles for simplified consisting and prototypical helper service, user loadable speed tables, a real network for layout operation with distributed system architecture (multiple PC’s), cost effective decoder harnesses, built in system upgradeability, plug ‘n play decoders for N scale, dispatch style operation (Utility throttles), momentary action key on throttles for horn activation, service mode programmer operates while mainline is running, fully customizable sound definition language for sound decoders.

Other DCC Companies: analog locomotive operation, zero stretching to allow analog locos to run on DCC, factory installed decoders on light boards, two part decoders for small installations, LCD walkaround controller, simplified “knobby” controller, back EMF speed stabilization, dual booster packaging, computer interface included with command station, backlit LCD display, fast clock on throttle display, variable frequency PWM, commercial kit decoders, operations mode programming, kit DCC command stations and boosters, sound boards included with DCC decoders, polyphonic sound integrated in DCC decoder.

Even though a particular innovation may be attributed to a particular company, often these innovations and features are quickly incorporated into products produced by other companies as well. This list is not meant to be all-inclusive but it will give you an idea of the caliber of engineering that goes into today’s DCC products.

10. Customer Service & Support

Customer service is another factor that differentiates the various DCC companies. Only you as a user can judge this area. We urge you to call, write or e-mail the various companies for information. Talk to your friends & learn about their experiences. There is a big difference.

Digitrax is a full time professional company. We have our own production facility, technical support staff and engineering staff. When you call there is a person who can answer your questions & take care of your concerns. If you need a repair done, we do it in house.

Each DCC company has it’s own company culture and profile. Visit their web sites and review their literature to learn more about them and how they do business. Some companies are large and some are small. Some are full time and some are part time. Some manufacture their own products and others subcontract their production. You will learn that there are DCC manufacturers all over the world and that they produce products for many different markets and styles of operation. The important thing is to find a company and system you are comfortable with.

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