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DCC – History

The idea of independent control of two locomotives goes back to at least the 1940’s, with companies like Ives and Lionel leading the market during those times.

It is important to realize that due to the nature of the electronics available in those days, most system were unreliable at best and often very expensive.

Ideas like “Progressive Cab Control” date back to the late 40’s, but again due to the available electronic components, was very complex to implement and costly to construct.

Advances in electronics, with the advent of cheaper, smaller and more reliable solid state devices, made even more things possible. It would take about 30 years for command control systems to go from analog to digital in the form of Digital Command Control (DCC).

The shift from the analog computer to the digital computer drove electronics to the present day’s powerful but small microprocessors that make Digital Command Control possible.

Let’s review some the systems leading up to modern day DCC..



In 1940, Lionel offered a new innovative product called the “Magic Electrol” – inside every Lionel locomotive they fitted a device called the E-Unit, that controlled direction using the “Magic Electrol.

The E-Unit was described as a solenoid operated rotary sequence switch. The Magic Electrol was used to control the E-unit. This allowed you to run two locomotives in opposite directions on the same track. Remember, Lionel used alternating current, so there was no way to flip the polarity. The E-Unit was originally developed by Ives, but lived on when Lionel took over Ives.

Instead of the usual method of controlling the E-Unit, where you cut track power to switch the E-Unit (forward-neutral-reverse-neutral) by pressing button 1, pressing button two (whistle) injected Direct Current onto the track that triggered the Magic Electrol unit.

After the US joined everyone else fighting the Second World War, Lionel ceased production of trains and Magic Electrol in 1942.

In 1946, Lionel introduced one of the first Electronic Control Systems –  the system was designated: 4109WS Lionel Electronic Set.

The Lionel Electronic Train Control system consisted of a one watt transmitter and a number of small receivers mounted under or within a piece of rolling stock.

The set included a massive cast metal 671R Turbine (based on the Pennsylvania S2 Turbine locomotive) for motive power, tender with whistle, a boxcar, gondola, ore-dump car and caboose. This was the second major post-war innovation from Lionel, after the smoke unit introduced in 1945.

While the PRR built only one S2, Lionel built a considerable quantity of the model 671 locomotive. The R in the part number indicated Radio.

Each car could uncouple anywhere, with the press of a button. The set was a technical wonder, and a maintenance nightmare. Troublesome operations and a $75 price tag (about $900 today) resulted in the system being discontinued in 1949. A sizeable problem was dirty track and poor rail joints. To counter this, stainless steel was employed for track and axles.

The set was withdrawn in 1949, a victim of its high retail cost and poor sales. These sets do command a good price on the collector market, but are rarely seen in operation.


Transmitter The transmitter was built around a 117N7GT vacuum tube that functions as an oscillator and a rectifier. Ten buttons controlled the operation of the oscillator, which produced RF signals from 230 to 350 kHz. This signal, measuring about 3 volts, was superimposed on the 60 Hz AC track power.


Each receiver is a series tuned circuit, with a rectifier and a relay. The receiver is tuned to a specific frequency, which activates whistles, couplers or a dumping mechanism. Two types of receivers were made. One type was for the locomotive, the other for rolling stock. The tender would have two receivers installed, one to operate the whistle motor, the other to control the reversing unit. The other type (of which there were four channels) operated the coupling mechanism, and in the case of the dump car, the dumping mechanism. To dump a load, the user simply held the button down for three to five seconds, which activated a thermal relay, which in turn controlled the unloading mechanism.

The channels were set up as 1/2 for the locomotives, 3 for the caboose, 4, boxcar, 5, gondola, 6/7 controlled the whistle motors, 8 was the dump car, with 9 and 10 being spares. The locomotives and caboose were fitted with RUB receivers, the boxcar was an RU, RUA for the gondola, RUD for the dump car, and the whistle was controlled by an RUC receiver.

The RUB and RUC were considered high frequency units, and the RU/RUA/RUD were low frequency units, channel 1 being the highest frequency. A complete RU-1 receiver was $5.00. Tuning was accomplished with a slug or plunger inserted in the input coil, which formed the primary of a transformer. A $2 tuning assembly completed the receiver.

Set Up The setup was like a command station/booster in two units. The transformer was connected to the Electronic Control Unit, and the ECU was then connected to the track. Lionel recommended feeders for long runs of track. The rolling stock was fitted with stainless steel axles to improve conductivity.

The vacuum tube used in the transmitter functioned both as an oscillator, and a rectifier. A 117N7GT is a tube with a 117 V filament (no filament transformer needed). It combined a diode and a pentode in the same package, the maximum voltage on the plate and screen was 117 V, and it was classed as a Class A Amplifier Half Wave Rectifier. Its power output was 1.2 W maximum. Lionel chose this device to simplify the design and keep the cost down.


Progressive Cab Control (PCC) is a concept that first appeared in 1949. It used multi-deck rotary switches to set routes, and power could be routed in a progressive manner by the dispatcher as the train moved along the track. The system would evolve, using relays and eventually computers to control and route power automatically using block detection to control the power routing.

A well known example using telephone switching equipment was built by MIT students at The Model Railroad Club on campus. Later it was upgraded to a computer controlled system implemented with relays. They also used a Digital Equipment Corp. PDP-11 to control their layout.

With the adoption of DCC, progressive cab control fell out of favour. Any DCC system can be purchased and installed for less money, and with a lot less complexity, than a progressive cab control system, which relies on costly rotary switches as its backbone. (Rotary switches with multiple decks that can handle the currents needed for Multiple Unit operations are very expensive, having been replaced by microprocessors and solid state devices). Later versions employed computers to handle power routing. The cost in labour and parts coupled with the wiring complexity of Progressive Cab Control meant very few successful implementations of the concept occurred. It was just too complex for a home layout, and even club layouts had difficulty implementing it.

Digital Command Control’s advantage was simplification of wiring, rendering schemes like progressive cab control obsolete. Operations were enhanced by the operator not having to worry about blocks when operating on a DCC layout. DCC is also more cost effective in terms of labour, wire, and control devices than methods such as Progressive Cab Control or C/MRI.



The 50’s did not see much progress in the field of model railways, with a lot of attention being given to the “Space Race” and recovery of the economy following the war.

EDCO was one of the few model railroad companies to develop and market new products, with “Model Railroading by Radio Control” being advertised and made available to the public in 1952. The system did not require a radio operator licence but sadly disappeared from the market after only one advertisement published in February.

It was available as a complete unit, kits, and individual parts so you could construct your own system. The plans were available for $1.95, which would be credited to your order if you bought $20 or more in parts.

The control system used a single vacuum tube transmitter, with ten channels, small receivers (which didn’t need a tube) that could be fitted to locomotives or rolling stock.

It featured constant voltage on the track, the control was on the train. EDCO stated you could control several trains on one track, uncouple, smoothly accelerate/decelerate, start and stop, and even reverse with no effect on another train operating on the same track.



The Sixties brought a lot of change, and that included model railroading. Command Control, or as it was often called, Carrier Control would benefit from the revolution set off by the transistor and other semiconductor devices.


Carrier Control indicates the control signals reach the receiver by wire (such as the track), whereas Radio Control indicates wireless transmission of the signals. In either case, a carrier, such as an audio frequency tone or a radio signal, carries the instructions to the receiver.

Linn Westcott made some observations in his December 1962 editorial for Model Railroader. One observation was that many carrier control systems were created by those who recently joined the hobby, and happened to be electrical or electronic engineers. They had lots of enthusiasm but lacked in-depth knowledge about the hobby and what it needed. The same effect was seen in transistor throttles. There was no real demand for carrier control technologies, as cab control had evolved and was well understood.

Westcott presented a number of features he felt were necessary and should be considered by those planning to design a carrier control system.

  1. Receivers should be as compact as possible so they would fit into the confined space of many locomotive bodies;
  2. Ability to move at both slow and high speeds;
  3. Locomotives should not interfere with each other during operations;
  4. No EMI/RFI which would cause problems with radios or televisions;
  5. Tuning should be possible without special tools or instruments, preferably while the locomotive is still on the track;
  6. Your track plan and wiring style should have no detrimental effect on performance;
  7. Compatibility with Direct Current, such as using DC for the motor, signalling, constant lighting, and reversal of polarity shouldn’t cause problems.

Between 1961 – 1962, a company called Track Master advertised the “Roundel Track Master”  (appeared in an advertisement in the September 1962 issue of Model Railroader).

Track Master claimed the capability to control several locomotives. The Track Master II also professed to eliminate many wiring issues such as reversing loops.

Outside of a few samples, the system seems to have never made it past the prototype stage, and was never sold commercially.

A preproduction sample of the Track Master was reviewed by MR in March 1963, the receiver was sizeable, and appeared to be installed in a boxcar. A third unit, the Track Master III was mentioned as well.

Sadly, it would be noted in later issues that the Roundel system never progressed beyond the samples MR received for review.

The idea of “Automatic Simultaneous Train Controls” however had been firmly embedded in many modellers minds, and as a result the manufacturers were being asked to produce a “Command Control System”.

One of the first Command Control Systems to enter the market was the ASTRAC K-2 , designed and manufactured by General Electric.











An improved ten channel version of the ASTRAC system offered by GE, developed and manufactured by Alphatronics.

Featuring 10 channels, compatible with ASTRAC, and additional channels were available by special order. A basic two channel system cost about $300, (almost $1000 today) and decoders were $40 to $50 (in 1979). Track voltage was about 19 V. Alphatronics began manufacturing a receiver compatible with ASTRAC transmitters in 1972, and announced a compatible transmitter in mid 1972.

It was described as a ten channel, AC carrier wave, frequency controlled system.

Alphatronics offered three configurations: A single fixed channel transmitter, a transmitter which allowed selection of any one channel using buttons, and a transmitter with a rotary switch to select one of ten channels. The transmitters could be ordered with tethered throttles. The throttles could be plugged in at remote stations. When the throttle was disconnected from the system, the train would stop. The throttles were simple units with a speed control and reversing switch.

Two receivers were offered. The A3 was a single unit about 3/8 x 1/2 x 1.5″, and the A4, which was split in two parts for fitting into a tight space. The receivers were often installed in a dummy unit. The A3 had enough capacity to handle up to three locomotives in a consist. The decoders were three wire types. The A3 retailed for $35.75, while the A4 was $50.

The Alphatronics system appeared in 1972, and was available on the market until 1981. The Alphatronics receivers also used a single TRAIC instead of the two SCRs used by GE’s ASTRAC receivers.


According to an answer published in the MR Clinic, August 1972 Model Railroader, Jouef of France made a very similar system to ASTRAC, which was never exported to North America.

Details from 1968 indicate it was a carrier control system, using an AC waveform on the track, tension (French for voltage) was 14V. Initially offering 4 channels, with the possibility of more in the future. The receivers were compact at 0.4″ x 0.5″ x .8″.

Philips may also have demonstrated a similar system but details are very scarce.









The era that spanned the early 1970s to 1989 spawned a number of command control systems. In the beginning they were analog, but early on systems using digital technology began to appear.

The Digitrack 1600 offered 16 channels. Manufactured by Electro-Plex Inc., of Urbana Ohio, it allowed change of channel in locomotive by changing a plug. First mention was in 1972. A basic four channel starter set sold for $339.95. Additional channels available at extra cost. The Digitrack 1600 system went out of production in 1975.

It was the first command control system to use digital control signals superimposed on a DC voltage (time division multiplexing), but the cost and complexity of the system doomed it. The equivalent price in 2013 dollars would be almost $1900.

The Digitrack 1600 Master Power Pack transmitted 16 pulses sequentially, one for each receiver. The pulse was nominally 250uS (microseconds), and could be as long as 500uS. Using timing, when the pulse began and ended in relation to a fixed point in time determined direction and speed. A sync pulse locked the timing of the receiver to that of the transmitter, allowing it to count pulses and determine the instruction intended for the receiver. The difference between the clock and the pulse determined speed and direction. Instruction pulses were transmitted 100 times a second.

Russ Larson reviewed the Digitrack 1600, demonstrated by creators Balmer and Robbins, in operation on Linn Westcott’s Sunset Railway and Navigation Co. in the August 1972 Model Railroader (of which he was the editor), and was impressed with system’s performance. This would lead to the CTC-16 project later.



Track voltage was a nominal 13.5VDC, the pulses were 4VDC.

If viewed on a scope, the waveform would show a DC voltage with sixteen 4V pulses riding on the track voltage, as produced by the Master Power Pack. Think of it as a 4VDC pulse with an 11VDC offset. There would be the sixteen pulses, then a period of low voltage (~11VDC) before the pulses began repeating, forming a synchronization pulse. The receiver module counted the pulses until it arrived at the one it was waiting for, which it then acted upon. The duration of the pulse, and its relation in time (phase) determined speed and direction.

This also gave the user the ability to use constant lighting, as the track was energized at all times.

System Configuration

The Digitrack 1600 was a three piece system: The master power pack, a control box (throttle) and the receiver. Additional auxiliary power supplies could be connected to the master power pack to increase the system’s current capacity to eighteen amps.

The master power pack was designed to supply 13.5VDC (nominal) to the track, at 4.5Amps. The receivers could output from zero to 12VDC to the motor. Current consumption was 100mA, maximum motor current one amp.

The address the throttle controlled by determined by which position it was plugged into on the master power pack. Sixteen plugs (or positions) were available, one per channel/address, using four position connectors similar to those used in computers to connect power to hard, floppy, and optical drives (prior to the arrival of the newer SATA peripherals).


Receivers for the Digitrack 1600 measured about three-quarters by one by one and three quarter inches. They could fit in many HO scale locomotives, or be installed in a dummy or tender if needed. Dual motored HO locomotives could be converted if the current draw was less than one amp in total. (The 1A rating was a nominal value, up to three amps peak was possible). The decoders were not powerful enough to handle O Scale applications, it is unknown if that ever changed. Electro-Plex did say they planned a 5A version for O Scale applications.

Due to size and the constraints of the technology, N scale was not supported. Future plans included the possibility of smaller receivers.

It was also possible to bypass the receiver using a plug or switch to allow operation on a Direct Current layout. Unlike Digital Command Control, a direct current locomotive not equipped with a Digitrack receiver would react to the constant track voltage by accelerating at full speed.

Double Heading (or consisting) was possible. The locomotives could be on the same, or different channels.

Miscellaneous Details

Reverse loops required a switch to swap track polarity, otherwise a short would occur. Flipping the polarity during operation had no effect on the motion of the train, as the receiver was not sensitive to polarity changes.

Re-invention as CTC-16

Model Railroader purchased the publication rights and planned to publish a series of articles on constructing and operating a Digitrack system. Upon review, it was determined to be too expensive for a do it yourself project, and the Digitrack 1600 evolved into the CTC-16 system that appeared in the December 1979 issue of MR. Digitack is compatible with CTC-16, which used more advanced components that were available at the time.

Another device called “DigiTrack” was unrelated, as it was a handheld throttle. Kato also called their system Kato Digitrack.



This carrier control system appears to have been another planned but never truly realized product from ARI-TRONICS of Scottsdale Arizona. Although advertised for about a year, there is little more know about the system outside of what was presented in the ads.

Advertisements for the unit appeared in mid-1971.

ARI-TRONICS offered the ability to independently control the speed and direction of up to five locomotives on the same track. The system was a solid state design, available in kit form or fully assembled, with the power supply included. It was described as a miniature frequency control unit for HO locomotives.

Later a lower cost two engine control system was offered in an easy to build kit, for $24.95, with support for N scale as well.


Mehrzug Elecktronic 80 / Multi-train Electronic 80

The ME-80 was made by A Fienwerktechnik in West Germany, and sold in the US by Janssen Enterprises.

An advertisement for the system appeared in the June 1976 issue of Model Railroader. It did not contain many details, but it did claim the ability to control up to six locomotives without the need for a block system, ‘forwards, backwards, fast and slow’ the ad stated. The front panel of the main unit pictured was labeled in German. It bore the appearance of a piece of high-tech electronic test equipment with it’s aluminum face, blue cabinet and a wire stand which raised the front of the unit.

The main unit had six slide switches, which allowed the user to set the hand-held unit’s channel. The front panel had the selector switches, indicator lamps, fuse holders and six DIN plugs for the hand-held interface. There were also the “Telex Crystal” (sound accessories), receiver crystals and rectifiers available to be installed in your motive power. Like many command control systems, it put constant power to the track and claimed to eliminate a lot of wiring.

Each channel used a pair of frequencies, one for forward and the second one for reverse operation, which controlled the receiver. A steam sound generator was also available which could add the chuff and whistle sounds.

The suggested price was $925 (in 1976, or $3800 today).


“Master Zone Layout Control

a Concept proposed in the mid 1970s by pioneering model railroader Ed Ravenscroft. It is based on Progressive Cab Control.

Control was divided between the Master, or dispatcher, down to the Zone which then connected the cab to the track (Layout).

The entire concept was to simplify the wiring while making it easier to control the flow of power. Again, while simplifying the wiring, it added a number of devices, making it a costly proposal. Details about the system can be found in the February and April 1974 issues of Model Railroader. One feature was the placement of controls for switches would be near where the operator would be, while being close to the switches themselves.

The underlying theory behind PCC and MZL was to simplify the wiring, reducing the complexity of operating a train. Both systems still required care and intervention on behalf of the engineer, distracting him from the operations of the layout.

Many command control systems attempted to reduce wiring complexity. Modern DCC has reduced the wiring, making operations all about running the train, and not interacting with power routing and control. The operator does not have to worry about crossing block boundaries, nor does the yard switcher have to use a string of cars to couple to a cut in another block, occupied by an active train. You control the train, not the layout.



A 16 channel system, superseded by the Railcommand system. Appeared in 1979. Model Railroader magazine published a series of CTC-16 articles as a do-it-yourself project. Based on the Digitrack 1600, with simpler construction using newer integrated circuits available at the time.

CVP Products was one of the suppliers of CTC-16 systems.


Another CTC-16 compatible system called CTC-16e appeared in 1984. Again, designed for people to build themselves.

The CTC-16e featured a dedicated throttle, or a selectable channel throttle which used what was called the T/BUS.

The dedicated throttle was built for a specific channel. The T/BUS throttle featured 16 channels, with a three wire connection to the system bus. T/BUS allowed channels 0 to F, which were digitally transmitted to the command station. The T/BUS throttle featured momentum, braking and throttle memory.


Another evolution of the CTC-16 concept, with 64 channels.


The DIGIPAC 316 was a commercial version of the CTC-16, manufactured by Mann-Made Products. It appeared in 1982, offering 16 channels. It claimed to work using Digital Proportional electronics, despite the fact it was an analog command control system based on the CTC-16 project published in Model Railroader.

Prices were as follows (for 1982): Power station, $61.50, control station $105.90, throttle with a knob was $19.95, or with pushbuttons, $17.85. The receivers were $39.50, channel selector plugs $5.95 each, and selector receptacles $4.95.

A selector receptacle was needed at every position you wanted a throttle to be plugged in. This was then wired to the control station. If you wanted to use all 16 channels, a 19 conductor wire would be needed. Wiring the receptacles was one of the most time consuming parts of the entire installation. The selector plug could be connected to any throttle and then plugged into a receptacle.

The system allowed “Plug Around” operation, which was their name for memory operation. The speed and direction would be maintained, but over time the train would slow to a stop if the throttle was not plugged in.

The receivers were designed to fit HO equipment without cutting. They were 11/16″ wide, 4 9/16″ long, and about 3/8″ in height, for the diesel (D1) version, and were capable of 1A surge and half an amp continuous. For Steam, the S1 was 1 1/8 X 2 3/4 X 1/4″, or the S2 at 1 1/2 X 2 3/8 X 1/2″, and offered the same current capabilities as the D1. Mann-Made promised receivers for N scale.

W. Alan McClelland installed the DIGIPAC 316 system on his Virginian and Ohio railroad, previously he had employed GE’s ASTRAC system beginning in 1963.

In 1984 the Dash II version was released, which allowed up to 32 channels. It was compatible via upgrade with the CTC-16, but not the CTC-16e cabs.

For a review of the DIGIPAC 316 see the September 1982 issue of Model Railroader. The same issue also features the DIGIPAK 316 being installed on a project layout. It is also mentioned in the November issue’s article on the V&O.


Planned software announced by Custom Control Systems in 1981, which would allow the dispatcher to control the model railroad from a computer, compatible with the CTC-16. The system would include software and hardware, with a design manual. Originally intended for the Radio Shack/Tandy TRS-80 computer, software was planned to allow other computers to be used. As a minimum, the system could control routes, cab signals, trackside signals and hump yards.

It is not known if this software package made it past the announcement stage.

Computer Throttle Control 80

A later, computer enhanced version of the CTC-16 was the CTC-80. It was the third generation of the Digitack 1600, and used a Z-80 microprocessor in place of the analog processor used in the CTC-16. Manufactured by Keeler Rail Specialities. It appeared in early 1988.

Required a personal (micro) computer to control the system. Compatible computers were the Apple II, the IBM PC, or the Radio Shack Model III, which interfaced to the CTC-80 via the serial port.

The system could operate in 16, 32, or 64 channel mode, for up to 64 locomotives under its control, and 16 throttles could be connected to the system. Channels 17 to 32 were reserved for computer throttles. The CTC80 receiver offered 64 channels, compared to the 16 of the CTC-16 receiver.

The command station was $400, a throttle $75, and receivers were $50. A power station control card was $30. The power station was only available as a kit, or the power station control card could be used to upgrade an existing CTC-16 system. The full setup was only required if there was no existing command control system on the layout, otherwise upgrading a CTC-16 system was possible with fewer components.


Power Systems Inc., introduced Dynatrol in 1978, now sold asClassic Dynatrol. Dynatrol is an 18 channel system (originally only 15 channels were offered), using a track voltage of 13.5VDC, and a frequency shift reversing system. It used audio tones to transmit commands. Additional channels were planned to control sound effects.

Dyntrol uses a supersonic carrier, with modulation of the duty cycle to transmit information to a pre-programmed receiver in the locomotive. Each throttle has its own oscillator and modulator, which are controlled by the throttle and brake controls. The carrier frequency is determined by a precision resistor installed in a small plug, called a channel plug. Reversing the locomotive is accomplished by phase shifting the carrier slightly. Receivers were available in various sizes that could fit N scale and larger locomotives. Multiple power supplies ($55 in 1979) and blocks were needed to reach the 15 locomotive capacity of the system.

Channels were selected using key plugs. Momentum and braking effects were also available.

The system has been on the market since 1978. Dynatrol and Onboard were among the most popular command control systems in use.

A basic direct or non-momentum cab cost about $65, and a full function cab was $75. Receivers cost from $50 to $60 each.


EMS was manufactured by Trix in Germany and sold by Walthers in North America. It used a 9.5 kHz carrier to control a locomotive with a receiver. It worked with an existing DC control system, allowing both DC (analog) and EMS equipped locos on the same track. A controller and receiver rated at 850 mA would have cost over $100 in 1979.

This system would be considered an AC/DC system. A high frequency AC signal was applied to the rails and the locomotive equipped with the receiver would act on the signal. This allowed independent control as the standard DC locomotive just ignored the AC voltage.

One locomotive was controlled by the power pack, the other by the EMS system, allowing the two to operate independently of each other. The EMS controller was a single knob for speed and direction. Additional parts made it possible to bridge gaps in the track work, enabling the EMS equipped locomotive to travel independent of the block boundaries by passing the AC signal while blocking the DC voltage.

A receiver was $35, and the EMS controller $75.


ONBOARD Locomotive Sound and Control

The ONBOARD Locomotive Sound and Control system, by Keller Engineering, offered 20 (originally ten) channels, with a constant 12VDC on the track. It used audio tones to control the locomotives. A base system was about $376 (1986). Wireless throttles were also available.

A typical starter set came with a 5A power supply, a 16 channel handheld controller, two 1A motor controllers and the manual. The handhelds generated both throttle and sound commands with crystal controlled oscillators. They used a keypad, with keys for the sound effects, throttle up and down. Bringing the locomotive to a stop and holding the throttle key would reverse the direction. The keys were colour coded, and each handheld could control two locomotives. Signals from the throttles were fed to a mixer, each mixer could support four channels generated by two handhelds.

The receivers were called throttles, and were installed in a locomotive or dummy unit. The ONBOARD system claimed to eliminate the need for control panels and block wiring.

It offered steam locomotive exhaust sounds, bell and whistle. For Diesels, it featured a variable engine RPM exhaust, bell and six chime air horn sounds, plus constant lighting. Another optional feature was directional lighting.

Another accessory was a signalling system, for use with lights or semaphores.

Technical details:

Motor controllers available in 500mA, 1, 2, and 4A versions, and also for garden railways. Built in memory, with pure DC out at full speed.

Steam Sound unit

Optical exhaust sync (or magnetic for outdoor use), automatic 2 stroke air pump, adjustable 6 chime whistle, bell.

Diesel Sound unit

Exhaust controlled by motor voltage. Selectable 6 chime air horn, bell. The synthesizer as Onboard called it was usually installed in a dummy, and powered by a rechargeable battery maintained by the track power.

Reverb unit

Up to 100mSec of delay, with controllable echo repetition.

All sound units featured a 1 W amplifier.


A radio adapter was also available, using a Futaba unit, which was directly usable in large locomotives.

Keller Engineering closed in 1994, and the founder, Bob Keller passed away in 2007. While the system has been out of production for more than 20 years, it is still in use today. Unfortunately most of the documentation was destroyed when the business closed.

MRC Protrac

Sometimes called the “ProTrac R/C 1”.

Protrac was a system announced in 1979 by the Model Rectifier Corp. The Protrac R/C 1 System 7000 controlled two locomotives, only one decoder equipped. It was an AC/DC hybrid similar in concept to the EMS system. According to a review in Model Railroader (November 1979), it didn’t appear to be radio based. The Protrac 7000 featured a dual throttle console, which looked a lot like an R/C unit for model airplanes.

The system works by using Throttle A (analog) to control the first locomotive, and a receiver using “Carrier Control” was installed in the second locomotive, controlled by AC signals (in the range of 8kHz) on the rails, using throttle B. The usual block control method was needed to run multiple trains.

The receiver would fit most HO locomotives, but was too large for N scale. The better option was to install the receiver in a dummy as it needed enough room to warrant removing some mass from the locomotive frame.

A later, promised R/C 2 System 9000 promised eight channels, with radio control for wireless operation. The Protrac system was not compatible with any sound systems that used track current to power them. At the time, the only compatible sound system was the Train Miniatures system which was battery powered. Other brands, such as the PFM (Pacific Fast Mail), Lambert Associates and Modeltronics sound systems were not compatible with this system.

MRC quoted prices of about $100, and $150. (1979)

Rail-Command 816

An eight channel digital signal system using a constant 12VDC on the track. Manufactured by Integrated Systems.

A single tethered cab that could control one locomotive sold for $14. A dual channel unit was $20. The locomotive would continue to run while its cab is unplugged. The throttle featured a single speed/direction knob, and a switch to enable momentum/braking effects. There was a brake trim control to allow adjustments for the characteristics of your locomotive.

Another part of the system is the throttle-transmitter unit. It was the power supply and signal generation system. Channels were selected by plugging a cab into one of the eight jacks on the unit. Additional power boosters were available to increase the power available. The 4 amp throttle-transmitter sold for $75, and the accessory 8A booster was $50. Receivers cost about $25 each. To allow for more flexibility, remote jack panels were offered for $11, as well as bulk cable to connect it to the system.

Stancal RFPT

The Regulated speed Full wave Positionable Throttle was a nine channel system using a constant 12VAC track voltage, and high frequency signals to control the locomotive. Handheld throttles (Throttle Control Unit or TCU) were $25 for a single channel or $50 for three channels. The Engine Control Units sold for about $53 (1979). A basic system (a triple TCU and three ECUs) was about $200.

The early units only offered six channels. The channels were fixed. Future systems promised nine channels.

The system was built around model aircraft radio control components. The ECU consisted of a servo motor driving a gearbox, which in turn drove a potentiometer controlling a transistorized throttle. The ECU also rectified the 12VAC to Direct Current for the motor. It was noisy during speed changes due to the servo and gear train.

The throttles featured rocker switches to control speed and direction. The throttles could only send one command at a time. Dirty track could result in loss of control.

Salota 5300

The Salota 5300 was a West German system imported into North America. It used a constant track voltage of 16-18VDC, and offered 5 channels. The Salota Power Deck/Control Transmitter featured 5 knobs that controlled the speed and direction of the 5 channels. It used a constant voltage of 16 to 18 VDC on the track. The Salota 5300 appeared on the market in the late 1970s.

It was suited to any scale that used 12 V motors. The control system measured 9.25 by 9.25 by 3 inches. Receivers measured 40 x 25 x 17 mm.

The system was advertised for $300 (including 2 receivers), and receivers were $40 each in 1979.

Airfix Multiple Train Control System (MTC)

An analog system introduced in 1979 by Airfix. Could control up to 16 locomotives, with a maximum of 4 at a time. The presence of an IF can on the receiver indicates it is a tuned carrier control system.

Main unit consisted of a console with sixteen selector switches to select one of four channels. (A, B, C & D), and trays for the hand held throttles (up to 4 could be accommodated). Track was energized with 20VAC at all times. Receivers were sold labelled as one of four groups, and part of install involved adjusting the tuning to the desired channel (one of 4 in that group) by adjusting the tuning slug in the IF can.

Prices were UKP 85.00 for the main unit, with two handhelds and two receivers. Additional handhelds were UKP9.95 each and receivers were UKP4.95 each. (In US dollars the prices would be approximately $179, $21, and $11).

A simpler two controller was advertised but never sold in 1981. Very basic with only two handhelds, and no channel selection. Airfix entered receivership at the time, which effectively ended the product and any future versions.


FMZ Fleischmann Multi Train

Fleischmann Mehrzugsteuerung

Introduced in 1987 by Fleischmann. The system is meant for use with two rail systems.

In FMZ multiple positive or negative pulses pulses follow each other. To the individual pulses still distinguishable there is a short zero volts pause, the so-called “Takt Pause”. The pulses are 28 microseconds, the cycle breaks are four microseconds. A positive pulse is seen as a logical “1”, a negative pulse is logic “0”.

The bits are always grouped into 8 pieces within a byte. To ensure that the message is understood the first byte is repeated but inverted. This signalling method has the additional benefit that the average voltage of the signal is zero.

This will allow an analog locomotive. An analog locomotive can now be controlled by adding a DC voltage on the track. Fleischmann planned from the beginning to allow analog locomotive operation.

Hornby Zero 1





Zero 1 master and slave units

A true digital system. Introduced by the UK manufacturer Hornby to the US in 1980, and Canada in 1981. It was a digital system based around a Texas Instruments TMS1000, a four bit microcontroller able to address and control up to 16 locomotives.

It was the most popular of all the command control systems in use by the mid 1980s. (Model Railroader reader surveys). Components can still be found for sale on the internet. Questions often appear on on-line forums asking about using a system someone got, or wondering if it is compatible with DCC.




MTR Services

Offered their Power Grid Systems command control system, which was compatible with the Zero 1 system, in 1996.


ZTC Controls

ZTC Controls in the UK still support the Zero 1 system and have made improvements to it.

ZTC also make DCC decoders that can be programmed to work with a Zero 1 system, and their controllers have a mode that enables control of a Zero 1 equipped locomotive.

One of the founders of ZTC was employed by Hornby as part of the Zero 1 development team.



ZIMO began offering a digital command control system ZIMO Digital (BGT-1, FP-2, FZE-2) in 1979, around the same time as Hornby’s Zero 1. The majour difference was the ZIMO system could control 99 trains and offered 16 speed steps. (Zero 1 only offered 14). Development began in 1977, with the product coming to market in 1979.

Zimo would continue to innovate, with computer controls and CTC capabilities. Zimo began selling NMRA compliant DCC systems in 1994.

Zimo Digital Signal Format

The Zimo digital signal is completely different from that found in the other digital systems. On the track is a DC power supply, superimposed thereon is the digital information in the form of short pulses of alternating voltage. The voltage is variable between 15 and 22V. The frequency of the alternating voltage is about 8.5 kHz, with the pulses having three different lengths. A pulse of 25 periods, the synchronization pulse, indicates that there is a new message beginning. The message itself consists of pulses of 5 periods (logical “0”) and 10 periods (logical “1”).

Between two synchronization pulses there are always 16 data pulses. The first 8 are the address bits. With these 8 bits 255 different addresses can be formed.

After the address follow 4 data bits for various functions, successively MZRL. M is for switching operations, Z is an additional function, R is direction, and L is the light. The next 4 bits contain the speed information, which allows for 16 speed steps.

Zimo Digital also has a special brake module for a stop section. If the signal is red momentary power interruptions are caused this module at the end of each synchronization pulse. These short interruptions cause the decoder to slow the locomotive to a stop with the set delay. All functions remain operable for the stationary locomotive.

Kato Digital

Also called Kato Digitrack

The Kato Digital system appeared in the late 1980s and was discontinued a few years later. Advertisements for a forthcoming Command Control System by Kato appeared in late 1986. It featured up to 100 addresses available, a primitive sound function, and capability to control switches, either with a controller or a computer via RS232 (serial port).

Capable of controlling up to 16 locomotives out of 100, with eight under simultaneous control. Up to 256 turnouts or other accessories. A square wave of +/-18V was present on the track, with the digital signals being present for the first 2mS of an 11mS pulse.

The system was proprietary, and decoders would only fit an HO locomotive (due to their size).

Basic system:

  • 4-501 Main Controller $420
  • 4-502 Subcontroller $160
  • 4-503 Switch Controller $160
  • 4-504 Power Supply $175

The subcontrollers, up tp three of them, plugged into the main controller, as did up to 16 switch controllers. With the addition off three subcontrollers control to eight trains at the same time was possible.

Locomotive receivers ranged from $70 to $80. Switch controllers cost $70, and the sound module was $7. One receiver was made specifically for a KATO JNR prototype locomotive, the other two (a 1A and 4A) were general purpose. The recievers where shown beside a ruler, ranging from 20 to 90mm in length.

KATO dropped the system in 1992.


Keller Digital

Keller Digital appeared in 1993. An advertisement in the January 1994 issue of Model Railroader (incidentaly, it’s 60th anniversary issue) described the new Keller Digital system based on the proposed NMRA Digital Command Control standard described in the October 1993 issue of Model Railroader.

Keller Engineering described the system as having 125 channels, conforming to the proposed NMRA standard, each engineer could control a train with four different channels for locomotives. They also offered sound, walk-around throttles, and the capacity to handle up to 32 throttles (and engineers).

No computer needed, but one could be used to control the system. Short circuit protection, with up to 10A capacity. It also offered full compatibility with the Keller ONBOARD system, which could share the track at the same time.

Keller Digital featured a microprocessor based system, and was claimed to be adaptable to any modifications to the proposed NMRA Digital Command Control standard via software update.

A starter system was offered at the introductory price of $495, consisting of a heavy duty transformer, power supply, command station, keypad (throttle) and two decoders. Existing ONBOARD system owners could upgrade for $350 by using some existing components.


Marklin Digital

Marklin Digital appeared on the market in 1984. This system was designed for use with Marklin’s line of Alternating Current HO trains. Developed by Lenz for Marklin. Uses Motorola parts, hence the different mode and compatibility settings. It is the system that uses the Motorola format for sending commands. It is not compatible with DCC, but some manufacturers support the Motorola format in their command stations.

The original format supported up to 80 addresses. Marklin and Arnold would market similar systems based on the Lenz design, Arnold would later exit the agreement due to patent/licence issues.

Two Marklin systems were sold: Digital~ for their AC products, and Digital= for Direct Current.

Marklin would also introduce another digital system developed by a third party for use with their DC product line.

Although Marklin Digital sold well in Europe, in North America it didn’t fare as well.

The system was first demonstrated in 1979, going on sale in Europe in 1984 and in North America in 1986.

Marklin/Arnold Digital Two Rail System by Lenz

Also sold as “Marklin Digital=”

Developed by Lenz (under contract), the direct current Marklin Digital= system appeared in 1988. Lenz digital technologies are not compatible with DCC, except those products marketed as NMRA DCC Compliant. Lenz was a non-model railroad company hired to develop a command control system as a subcontractor.

The format was originally developed for Märklin and Arnold to digitally control trains on two-rail systems. The data format consists of a voltage between the +18 volt and -18 volt with two different pulse lengths.

Long pulses are 100 microseconds, short pulses are 58 microseconds. A long positive and a negative pulse form a logical “0”. A short positive f a short negative pulse are considered a logical “1”. The decoder looks only the positive pulses. If the signal is reversed the sequence of short and long pulses remains the same.

Marklin Digital (Three Rail)

Märklin began hinting that it was developing a new command control system at the Nürnberg Toy Fair in 1979. Märklin officially introduced their Motorola based digital system, developed by a relatively unknown electronics contractor with most components built by Märklin. The system came to market in 1985.

In subsequent years, another contractor, Bernd Lenz, would also do contract work for Märklin, producing locomotive decoders and, later, Märklin’s first DC command control offering.


Marklin DigitalFX

An extended and improved version of Marklin Digital, using the Motorola II protocol.


A simplified cost reduced system which could control up to four locomotives

Märklin Digital (mfx)

In 2004 the new Märklin Systems digital control was unveiled. Developed by ESU with all components initially made by ESU for Märklin. “Märklin Systems” was dropped and once again the system is known as “Märklin Digital”.


Trix Selectrix

Digital system that appeared in 1982. Reintroduced in 1987 as “Selectrix”. Very small decoders, but more expensive (single supplier) than DCC. Trix is now part of Marklin, and the brand is used to identify their Direct Current products.


Not much is known about this system. It appears to have been another do-it-yourself system, published in 1988 by Model Railroad Craftsman. There were a number of articles about constructing it, including a Diesel Sound Module. It was capable of controlling up to 112 locomotives and was a derivative of the CTC-16 system.


Who were the leaders in Command Control up to this point?












The March 1984 issue of Model Railroader had an editorial about Command Control systems.

Their 1983 annual reader survey revealed that about 10% of the respondent’s layouts had some form of Command Control system.

The systems in use were found to be:

  • Zero 1: 24%
  • Onboard: 22%
  • Dynatrol: 18%
  • CTC-16: 11%
  • Other: 25%

As shown, no one system was a clear leader. The largest installed base was Hornby Zero 1, a digital system, the balance were analog command control systems. None were compatible with each other either. The other 90% of model railroaders were using analog (direct current) control with blocks.

Reviewing the various command control systems listed here shows why the NMRA’s Digital Command Control has succeeded:

  • No two command control systems were compatible with each other.
  • They were all unique, and being mainly built around analog technology, compatibility was not really possible.
  • The digital systems were costly and vendor specific.
  • Many, if not all the command control systems on the market, were proprietary systems, manufactured and supported by a single company.
  • When a company went out of business, their product line died with them.
  • Or as demonstrated by ASTRAC, when General Electric lost interest, they halted further development and cancelled the entire ASTRAC product line.
  • Hornby’s owners went into receivership shortly after the release of their Zero 1 system, delaying new products and effectively killing future development of the Zero 1 product line.
  • Command control systems were expensive and completely incompatible further hampered their widespread adoption.
  • A fragmented market with expensive products prevented one command control system from becoming dominant, in addition to the lack of large players which could supply and support their products over the long term.
  • In turn, that slowed adoption as many modellers chose to forego command control mainly because of cost and compatibility issues.
  • Conversion to command control limited the ability to interchange with other layouts, while requiring an investment in additional throttles for operating sessions.
  • The model railroad market was hesitant to invest in any expensive command control systems with the ever present threat of discontinuation.
  • Another key factor was future expandability, or lack thereof.
  • Most command control systems were limited by the current analog technology, while digital systems, with expensive components like microprocessors, were limited by the cost of the technology available to them at the time.
  • Those circumstances limited features such as the channels available to the user, unlike DCC which can offer almost 10,000 unique addresses to the user.
  • Today’s DCC has benefited greatly from the availability of a wide assortment of low cost components. Multiple suppliers offering products compatible with the NMRA DCC standards allowed for expandability and enhancements never considered possible prior to DCC.


Towards DCC

In the late 1980s, Bob Keller (Onboard Systems) approached the NMRA with a new technique to transmit digital signals to locomotives.

He presented a protocol and suggested that it be the basis of a command control standard.

His proposal was discussed but no agreement was reached, despite considerable interest.

In 1991 Tom Catherall proposed that Marklin’s protocol become the basis of a command control standard.

In early 1992 a meeting was held, and it was decided that the Marklin protocol had possibilities.

The NMRA created the DCC Working Group to examine the idea.

  • The first thing the WG decided was that the best chances for long term success lay in evaluating all the alternatives.
  • They realized that many NMRA members had already invested heavily in command control systems, and would be unwilling to convert to a new system.
  • Despite that, the WG decided to forego backward compatibility.
  • The first order of business was to create a list of requirements, which were published in the Clinic Book issued at the 1992 NMRA Convention.
  • This list was used to evaluate current command control systems and technologies.
  • The initial plan was to present multiple technologies as candidates for a standard.
  • The WG evaluated a number of command control and computer systems, but as time passed, it became apparent that one approach met the requirements, and while the original Marklin proposal could not satisfy the requirements, a sister protocol used by Marklin’s two rail systems could.

The decision to use Lenz as basis of the NMRA..

  • Marklin’s two rail command control systems were designed under contract by Bernd Lenz of Lenz Elektronik, and had the greatest potential to base a standard upon due to its signalling technique.
  • Rather than superimposing a digital or analog carrier on the direct current voltage, it combined them.
  • Power and Signal were the same thing, making the signal as strong as the track voltage.
  • The typical command control systems in use at the time required wiring to a high standard to prevent signal loss.
  • The Lenz approach was a lot more tolerant of less than perfect wiring, making it applicable to the typical layout.
  • The system was already deployed in Europe and had demonstrated its robustness.
  • The original Lenz protocol had additional desirable features, such as the ability to determine the power source available.
  • It made decoders which could operate on DCC or analog layouts possible.

The DCC WG wanted to create the best options for the DCC Standard, so while the key attributes were already available in the Lenz/Marklin protocol, numerous improvements were made to the protocol – Lenz off coarse happily responded by implementing the improvements into their core DCC system.

The DCC Proposal

The DCC requirements and proposal was presented to the NMRA Board of Trustees in 1992.

The proposal was for a single digital command control standard.

The resulting proposed standard was too complex, yet too simple at the same time.

  • Some felt it was too complex and feature rich, others felt it went beyond the basic requirements of interchange.
  • Still others felt that the proposal would stifle innovation and technical development of command control.
  • To solve this issue, the basic requirements were implemented in two standards, S-9.1 and 9.2, to satisfy the requirement for basic interchange, while the advanced features were incorporated into additional standards.
  • Some requirements were deliberately left out, such as command station architecture and motor control methods.
  • The separation of basic, advanced and Manufacturer Unique features allows the DCC standard to satisfy everyone without compromising the ability to innovate.

This would allow manufacturers to choose if they wanted to include more advanced features, or just make a basic system.

Systems could compete in price or features.

The NMRA defined the signal on the track, how it gets there is up to the manufacturer.

The same rule applies to decoders:

  • They can be simple, basic function low cost decoders or feature laden sound decoders.
  • The customer wins with choice.
  • The consumer also reaps the benefit of declining cost of the technology , where more features become possible at a lower price.


  • Many of the advanced features of NMRA DCC did not exist in the original Lenz protocol, and were added by the WG.
  • Since the NMRA cannot endorse or standardize a proprietary product, a potential standard cannot contain copyrighted, proprietary or patented components, Lenz GmbH agreed to the NMRA request to release all their rights to the technology for sale outside of Germany.
  • This would allow other companies to enter the DCC market freely, without the requirement of seeking a licence from a competitor.
  • It also allowed everyone to be on the same footing with respect to features.
  • The DCC WG further improved the DCC Standards so that no infringement would take place if the product were to be sold inside Germany.
  • While the signalling techniques are built around those of the Marklin / Lenz system, numerous improvements by the NMRA DCC committee created a packet format richer in features to Lenz’s command control technologies – Lenz, to their credit realizing the opportunity and also the importance of standardization, happily complied and worked closely with the committee to develop the first DCC NMRA compliant system
  • The NMRA DCC standard was not specifically based on the Marklin/Lenz system, but the Marklin/Lenz system presented the closest match to the NMRA WG requirements, and as Lenz had proven that their system was robust and able to cope with future demands, their system was chosen as the system of choice.
  • Due to the agreement between Marklin/Lenz and the NMRA, Lenz technologies and patents and copy rights became
    “Open Standards”.
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