The differences between the various DCC systems don't really show up when looking at the simple point-of-sale brochures. All will allow several trains to be driven; most are greatly expandable. Key issues to look at for larger railways are:
- Are there any limits on how many trains can be selected?
- Are there any limits on how many accessory devices can be controlled?
- Are add-on units for the command bus available to control signals?
- Are modules available that allow points to be controlled by "push button and LED" panels?
- Are there any performance limits for the command bus?
- Can it be connected to a PC for computer control?
- How is locomotive & decoder programming done?
Answers to some of these questions can be hard to find. Let's address them in turn:
- In practice, on many "large" layouts it turns out that only 5 or 6 trains are likely to be moving at a time. Beyond that it becomes too difficult to understand the operations going on. So limits about how many trains can be rolling at a time are unlikely to be an issue: most systems will allow at least 10.
- Each locomotive will have to have a unique number. Commonly, this is related to the "cab number" printed on the side of the loco. It is common to choose either the last two digits or last 4 digits to select the loco; that way, you will know the number just by looking at the loco. Unfortunately, some "low cost" systems limit the range of numbers that can be assigned to locos. These systems might become a limitation as the roster grows.
- Add-on accessories are critical, and mark a big difference between the available systems. All DCC systems will allow point control, and by wiring LEDs to accessory decoders they will all allow manual signal control. Going much beyond that, however, you need to start researching carefully. I wanted to be able to control points in engine sheds & yards by using pushbuttons - "the way you used to". CML Electronics' Tower Master unit allows this. I also wanted automatic signal control; the CML Electronics Signal Controller has been designed for just this.
- The two common command buses are LocoNet (used by Digitrax) and XpressNET (used by Lenz, Hornby, ZTC and others). The differences between these are to a significant extent theoretical to most users: they are unlikely to show up. Ignore the claimed speed issues: they will not affect you. However as a product developer I wanted to be able to add additional messages to the net; LocoNet allows this much more readily.
- PC interface to either network is available. For LocoNet, the Locobuffer is an excellent interface and permits a range of readily available PC applications to interface to the command bus. Additionally, it is possible for developers to create their own applications too.
- Does it have a proper programming track, to allow safer locomotive programming? All systems allow locomotive decoder programming. Only some have "all feature" programming. There is a capability for "live" programming, but that doesn't look very useful to me. Some systems use the normal track power output for programming, and enter a special mode. THIS IS DANGEROUS: if you forget to switch over to a special programming area of track, ALL locomotives will be programmed with the same information. This would be bad!
If there is a single bit of advice here: write down what you want, and choose a system that delivers it. Don't choose just the throttle and worry about the rest later!
Ultimately, the selection criteria led me to the Digitrax system. It had all of the features that I wanted, and I judged it to be more expandable than the others. Having made that decision, selecting a "Chief" system was obvious: the "Empire Builder" is a poor second, with programming on the "main" track output only. (The newer "Zephyr" entry level system is a good system, but wasn't available when I started; I may well have begun with that if it had been there).
Was this the right decision? Well, as at today there are prettier command stations, but they all do the same thing. Only the CML Electronics products do what I wanted by way of panel control and signal control. That's good enough for me.