# Lionel large scale TMCC is dc powered



## tommyheadleycox (Oct 15, 2010)

While poking around for info about my own Lionel large scale GP-20 A/B set, I learned some stuff that others might find interesting. Stop reading now if you’re already yawning. First: Here is a link that shows all the large scale diesels that Lionel ever made:
http://www.lionel.com/CustomerServi...t&doAction=search&product=8-850&productNumber

Only the last 2 models, after 1998, were Command Ready. The following is direct quote language from the Lionel service manual for their large scale/G scale Milwaukee Road GP-20 diesel.

Command Control Upgrade
•	This upgrade is made using kit 6-22960, which includes a radio circuit
•	and an antenna.
•	TO OPERATE IN COMMAND, YOU NEED A COMMAND BASE AND A CAB-1 REMOTE.
Preparing Your Layout For Operation
•	Your track remains DC* powered with a minimum suggested power rating of 135 watts required to operate your upgraded model.

How can it stay DC powered and still be digital? Strange. This is only true in Lionel 2 rail large scale.

Tommy


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## Greg Elmassian (Jan 3, 2008)

DC on the track with a "carrier" signal riding on it, just like MTH DCS. The locomotive separates the "signal" that is "riding" on the DC to get the commands.

I don't know the specific frequency or amplitude or modulation of the signal.

Greg


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## Chucks_Trains (Jan 2, 2008)

Boy have you got that all wrong!

TMCC is basically a radio system where the transmitting antenna is part rails and part ac house wiring. No power on the rail doesn't stop the TMCC signal from transmitting. TMCC equipped engines have an antenna that receives the signal...again nothing to do with track voltage.


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## Greg Elmassian (Jan 3, 2008)

DCS will work as a carrier on the rails, if the voltage is zero, then all you have is the DCS signal.

You now say that DCS is also broadcast on the AC power? So did it get there? The AIU transmits the signal out of the other end of the box (the power input) and then goes back through the power supply to the AC house wiring?

That is completely impossible, besides wrong. Show me the place this is stated by MTH, or for that matter anyone else... I really want to see this.

DCS uses a carrier frequency of 3.27 MHz, and I can document that.

You need to talk to an electrical engineer and ask if this is how it works. But I guess you would not believe him either.

Greg

p.s. if DCS really did feed 3.27 MHz back into your house wiring, the FCC wants to have a talk with them, they are violating the law.


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## Chucks_Trains (Jan 2, 2008)

This discussion is about TMCC 

See the thread title??!! Lionel large scale TMCC is dc powered


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## Greg Elmassian (Jan 3, 2008)

Sorry, I thought this was the normal harangue from Chuck about MTH DCS since I compared TSMCC to DCS.

Back to TSMCC...

From Trainfacts.com (one of the few technical resources):

The Lionel TMCC Command Base (Base) receives, interprets and retransmits commands from a TMCC CAB-1 handheld controller. The Base outputs include a signal that transmits through the outer rails of the layout at 455 KHz to locomotives and accessory devices, and a 9-pin pseudo-RS232 port that can drive power and accessory controls that utilize the RS232 protocol at 9600 baud. The 9-pin connector can also be used for bidirectional communication with a computer, in which case incoming TMCC commands generated by the computer will be echoed on the outer rail signal and the 9-pin output.

The power source is a special “wallwart” AC transformer with a 3-pin molded AC power plug. Unlike most wallwarts, the Lionel unit connects one leg of the low-voltage AC outlet to the “U-ground” safety grounding pin on the AC plug. THIS CONNECTION IS NECESSARY FOR THE TMCC SIGNAL TO PROPOGATE PROPERLY!! This link from the Base to the house wiring is an essential part of the antenna system for TMCC.

Both the Powermaster and the Command Base have radio receivers tuned to 27 MHz for receiving commands from the CAB-1 handheld controller. The exact frequency is controlled by selecting a pair of crystals for the CAB-1 and Base. The crystal in the CAB-1 is set to a frequency that is 455 KHz higher than the crystal in the Base. The normal frequency pair is 27.255 MHz (Channel 6) in the CAB-1, and 26.800 MHz in the Base. The reason for the 455 KHz stagger will be described later. (Note that the plastic holders for the crystals both say “27.255 MHz” even though the receiver crystal is really 26.800 MHz. The actual frequency is printed on the shell of the crystal.)


The receiver’s antenna consists of 28” of 26 gauge wire wound in a rectangular spiral pattern. (Always check the antenna’s attachment wires after servicing to verify that the wires have not fractured where they enter the PC board due to twisting and turning of the PC board to replace components.)


I stand corrected, it is still a carrier technically on the rails, whether DC or AC.


Further from the site:


The primary function of the Base is to control locomotives via the signal transmitted through the track (and the house safety ground wiring.) The transmitted signal is quite similar to the signal from the CAB-1 except that the *carrier *frequency is 455 KHz rather than 27 MHz.


A fine point, but basically the signal is a carrier on both the AC lines and the track.


But it is indeed unique that the power transformer is designed specially to feed the signal through the house wiring... weird, because the rails are always closer to the locomotive than the house wiring by a huge amount.

So the answer to the OP is that it is a digital signal using FSK, and that signal is ADDED (a carrier) to the track power, just like DCS does. Just like DCS you can add the signal to DC or AC. The signal really does not care what track power it is added to (does not care if the carrier is AC or DC).

Sorry for all the derailments.


Regards, Greg


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