The NMRA has implemented a program whereby manufacturers submit various DCC products for "Conformance" testing. If the product is found to "conform" to all applicable areas of operation, it is awarded a "Conformance" seal. However, in my opinion, there needs to be more work and thought in what the purpose of conformance is, and in the testing procedures themselves. I'll explain later.

Digitrax lists several different systems, including the Super Chief. Further, they offer all Chiefs in radio control versions. Then there are two or three Lenz sets, MRC Command Prodigy Advance, North Coast Engineering (NCE), Atlas, Bachmann and others. Further, there are many companies that make DCC- compatible ancillary equipment, such as Loy's Toys.

So, what do "Compatible" and "Conformance" mean to you?

Well, it's still buyer beware, because what's best for one may not be best for another. A product that might be best for you may not have a conformance seal, for whatever reason, while another product that has a conformance seal may not even come close to doing what you want. The following is a simple example:

One of the systems that have a conformance seal is the MRC Command 2000 - an entry-level system that has been discontinued. If your layout is capable of having more than 10 locos, or you want to run more than 3 at a time, this system will be below your needs (it's not that this system can't run more than 3 at a time, but it becomes cumbersome to do so). Not only that, it can't operate a horn and bell, control turnouts, or do any number of other "common" things that most other systems can do. Digitrax's Zephyr, for example, is capable of running up to about 10 trains at once, and can control turnouts and sound systems. While the Zephyr is DCC-compatible (it can operate all other manufacturer's DCC-compatible decoders), it does not have a conformance seal - because it has never been sent in for testing.

Does this mean that all you have to do is look for the "Compatibility Logo?" No, not any more than for the "Conformance" seal. First, not all manufacturers use the Compatibility Logo on their compatible systems. Further, the logo and/or seal doesn't say anything about what features the product has (except for the baseline standards). Following is another example of what I'm talking about:

Let's say you have a Zephyr system. It provides for 14, 28, and 128 speed-step modes. And, since 128 speed steps gives you the absolute best control, with the smoothest operation, that's what you will probably use the most. MRC decoders carry both the DCC-compatible logo and the Conformance seal, but that doesn't mean that they will do the 128 speed steps you want.

Conversely, if you have a system that does only 14 or 28 speed steps, purchasing a Digitrax decoder that can do 128 speed steps won't give your system 128-speed-step capability. It will be able to use the Digitrax decoder only in the 14 or 28 speed-step modes.

So, in reality, what really counts is that the products you buy will do what you want it them do - not only that it can do it, but that they can do it with the system you have. This is why using a DCC dealer who really knows how it all works is important.

So, if it's still buyer beware, what good are the NMRA's DCC Standard and RPs?

Plenty. It provides a platform whereby DCC decoders are capable of operating on any other DCC system. This allows you to take your locos from your DCC-controlled layout, to another DCC-controlled layout, and have it work properly. Further, with most DCC decoders (all but the early Wangrow) you can even take them to a DC analog layout to operate - without any physical modifications. Refer to Benefits of DCC for more information. The following text will provide you with more background about how DCC came to be.

In the beginning, model trains were controlled with a rheostat that would vary the voltage on the track. This varying voltage would make the trains go at varying speeds.

Some locos had DC motors. For these, reversing the polarity would reverse the direction of the train. Some locos had AC motors. These motors had one set of windings that make the motor go one way, and another set that makes it go the other way. A flip-flop relay was used to direct the power through one set of windings or the other.

When transistors came along, model railroad throttles were designed with a plethora of new features:

The next advancement was command control. This system has full constant voltage on the track and a device (receiver) in each loco that acts as a remote-controlled electrical valve to pass only part of the track voltage to the loco's motor to make it go whatever speed you commanded. So, instead of controlling the voltage and polarity on the track to run the train, you actually control the train itself.

The first of these command control systems used radio-frequency signals to control the receiver - not in the wireless sense, but with radio-frequency signals being sent through the track along with the DC voltage that runs the loco's motor. Later versions of this type system use an analog control signal superimposed on top of the DC voltage.

Early versions of these system had many problems to overcome: drifting frequencies, dirty track interfering with control signals, etc. Each developer went about solving problems in different ways - wider bands with fewer locos, redundancy, error checking, etc. Because each developer solved these problems in different ways, no two systems are compatible with each other.

Some of these systems were available to be built from scratch, some came in kits, and others came fully assembled (some of these systems are still available). Regardless, it was expensive and required a lot of attention to make it work properly. Generally speaking, only the most fervent model railroader converted to command control.

Command control opened up model railroad operations like nothing before. For the first time, model railroads could be operated like the real ones - complete with MUing anyplace on the layout, and helper service without regard to electrical blocks. So, regardless of the expense and difficulty, it was an absolute must for prototypical operations.

In the early 1990s, a group of people in the NMRA recognized the importance of command control for operating model railroads. However, if the mainstream user was ever going to afford, and accept it, something would have to be done about compatibility. They decided that having a standard of some sort would be necessary for manufacturers to build compatible systems. This would foster competition among companies, encourage new features in equipment, and keep prices down.

So they started out by looking at all the systems that were available around the world. They looked at all the American frequency-type command control, and they looked at the German digital systems. They analyzed the advantages and faults with all the systems and made their decision.

What they came up with was such a stroke of genius, and so simple, that most people still don't fully understand it. Keeping with the "KlSS" (Keep It Simple Stupid) philosophy, they took the system to it's lowest common denominator - the signal on the rail.

It has always been traditional for individuals to take their favorite rolling stock (locos and cars, but not throttles) to clubs and other friends' layouts to run. So, they decided that if they came up with a track power/signal standard, that the most important compatibility need would be satisfied. That is, if there is a track signal standard, all manufacturers' loco decoders (receivers) would be able to run on any other manufacturer's system as long as that track signal standard was met.

The icing on the cake would be to add a feature where the system could run one DC analog loco that did not have a decoder, and all locos with decoders could run normally on DC analog layouts. This way, locos with decoders could not only be compatible with all other command control systems with this standard, but also with all DC analog layouts, and vice versa.

The system they found to have the most potential was a German system called the Lenz Digital plus. Bernd Lenz was gracious enough to place his technology in the public domain so the NMRA could use it as the basis of the standard. This, of course, placed Lenz as the immediate leader in the NMRA's DCC industry.

The main difference between this DCC system and the frequency-type systems is this: instead of superimposing a small analog radio frequency on top of the DC power that runs the loco motors, this DCC sends digital signals that have enough power to run the loco motors. As you can see, this main difference has two components: the makeup of the signal (analog vs. digital), and the sending of that signal (small signal superimposed on the power vs. the signal being the actual power itself).

Analyze this for yourself. Why do you prefer digital TV and/or sound recording over analog? Because digital provides cleaner, clearer, pictures and sound. That's because digital is more accurate than analog. Next, which signal will be more stable: a tiny AC signal superimposed on a larger DC voltage, or a signal powerful enough to run several locos? No contest. And for those of you who know and understand the difference between analog and digital, which do you think will be more open to future advancements and upgrading? Again, no contest.

Now, this doesn't mean that current frequency-type command control systems won't work properly, or even that one frequency-type system isn't better overall than some DCC systems - Rail Command II by CVP is far superior to the MRC Command 2000.. It just means that overall, all things being equal (similar price and features), digital is better. Anyway, that's my opinion - after spending more than 15 years in the computer industry and being in this industry since 1994.

In an effort to accommodate the products (Lenz) that were already built around this system, the NMRA adopted it's features as the "Base Standard". This encompasses the digital packets that are sent to the loco decoders for control, and how that signal will be placed on the rail for power. That's it. Just the rail signal, how it's placed on the rail, and how it will be used by the decoders. Refer to How DCC Works for more information.

This baseline packet includes several things, such as preamble, start bits, address byte, instruction byte, error detection byte, and packet end bit. The address byte provides for 127 different loco addresses. The instruction byte includes 14 speed step and function 0 control. There are also provisions for advanced features, such as more speed steps, more functions, and lots and lots of other stuff - stuff that can boggle the mind.

The key here is that since all DCC equipment starts out with this baseline standard, all DCC decoders will work on any other DCC-equipped layout - at least in this baseline 14 speed-step mode. That is, baseline decoders can be operated in the baseline mode even on an advanced system layout, and advanced decoders can be operated in the baseline mode on a baseline system layout.

The advanced features are covered in what the NMRA calls Recommended Practices (RPs). The name "Recommended Practices" for these "standards" is misleading. A better term would have been "Optional Standards". That is, the manufacturer doesn't have to implement these features, but if implemented, they MUST be implemented in the way specified.

For example, if a manufacturer provides 128 speed steps, or extended addressing (addresses beyond 127), it must be done in the exact way prescribed in the RPs. If it isn't done that way, another manufacturer's system would not be able to access it.

While you can take a loco from one DCC-compatible layout to another, you can't generally intermix throttles*. For example, you can't use a SystemOne throttle on a Empire Builder system, and you can't use a Lenz throttle on a SystemOne. There are some exceptions: Empire Builder and Chief throttles are interchangeable because they are both designed and sold by the same company, and SystemOne and NCE throttles are interchangeable because they were designed by the same person.

* SIDE NOTE: When throttles became more than a method to increase and decrease speed (i.e., also being able to control lights, sounds, and other things) they became known as cabs by some people - likening them to the controls available in the cab of a real locomotive. Some people still refer to them as throttles. Since we started out calling them throttles, we'll continue with that.

Many people errantly think the throttle should be included in the DCC standard - so you'd be guaranteed that you could take your throttle to another DCC layout. But, in my opinion, this not only would be wrong, but could be disastrous. Here's why.

There are currently three throttling methods being used on DCC systems. Starting from the oldest to the latest technology, they are: hard wiring, such as that used in the now discontinued MRC Command 2000 system (the lowest cost, but most limiting, method), a polling system such as used with Lenz Digital plus, Wangrow SystemOne, and NCE, and peer-to-peer network system such as used with Digitrax's Zephyr, Empire Builder, and Chief systems (the latest, most versatile, technology - similar to Ethernet local area networks used in modern business environments).

If a throttle standard had been set from the get-go, which would have been chosen? My choice would be for using the latest, most versatile, and best technology available: peer-to-peer network. But that would have precluded the use of hard wiring to produce an ultra-low cost system for people with 4' x 8' layouts. How would that benefit the hobby? And, if they had chosen the polling network system, that would have prevented anyone from using the newer peer-to-peer network technology. How is that a benefit to the hobby?

And if a standard is set today, which one would be chosen? The one that has been in use on digital command control the longest (Lenz), the one that has been in used in model railroading the longest and also at the lowest cost (MRC Command 2000), the one that most companies use (SystemOne and NCE), the one with the latest and best technology which is also the one with the most systems already installed in the U.S. (Digitrax's LocoNet systems), or something completely different? Whichever one is chosen, it would obsolete all the other systems that are already out there. How does that benefit DCC or the hobby?

My suggestion is this: If you want your throttle to be compatible with your club, or your friend, buy what your club or friend already has. But, if your preference is to have the throttle system that suits you best, why would you want some committee to decide what's best for you? The DCC working group was wise enough to recognize the difference between compatibility of loco control and throttling systems, and that loco compatibility would improve the hobby, and that including a throttling standard would limit it.

I hope by now you can see that we're talking about two completely different aspects of controlling a train (the throttle system, and the track power/signals), and that it would be counter productive to tie them together under the same set of Standards. I think great credit should be given to the people of the DCC working group, who must have been tempted to encompass more than just the track signal into the Standard, but managed to squelch the urge.

To sum it up, DCC is a Base Standard and set of Recommended Practices (RPs) that spell out how the power and signal will be placed on the rail, and how decoders will use that power and signal. This facilitates being able to use decoders made by any DCC manufacturer, on a layout that is powered by any other manufacturer's DCC system - i.e., if the system has the proper DCC signal on the rail, a loco with a DCC-compatible decoder will run on it. It has nothing to do with throttle connection and operation. And, aside for a few exceptions, throttles are not interchangeable between different manufacturer's systems - yet.