Tuesday, May 31, 2011

Lionel Legacy/TMCC Ground Plane Issue and other Miscommunications

My Lionel Legacy ES44AC was stopping at certain consistent points on the track at medium speeds only.  When powered up, the headlight on my 1990's-era TMCC GP7 would blink intermittently.  Both engines would not respond well to commands.  With much troubleshooting and some help from the OGR forums, I determined I had a "ground plane issue."  Not aware of this, I set out to research what this was all about.

Apparently, certain areal conditions like parallel tracks, metal structures, and overhead tracks can cause interference with the Lionel TMCC signal in a particular spot on a layout.  To test for this condition, you hold your hand over the moving locomotive in the problem area and if it works without problems then it is assumed that you are improving the "earth ground signal" in that area and you have a "ground plane issue."
My Lionel Legacy ES44AC diesel stopped at a consistent point on the track in this corner of my layout:

The commonly accepted solution to this ground place issue is to run a parallel wire along side or under the track in the affected area. One end or the wire will not be connected to anything and the other will be attached to an earth ground. NOT the common of the layout but earth ground, for example a nearby electrical outlet ground screw or box or a water pipe know to be earth ground. The wire can have insulation on it or not, but it is preferred to avoid shorts with other wires or track in the area. Gauge and type of wire does not seem critical.
I attached a solid 12-gauge wire to a nearby water pipe and haphazardly draped it over the corner of my layout. It worked! The engine ran many loops without stopping. Further investigation revealed that simply draping the wire over the corner of the layout WITHOUT attaching it to the water pipe worked just as well in this case.  So what about the non-responsive TMCC diesel with the blinking light in the yard? Laying a ground wire near that attached to a nearby water pipe fixed that too!

I was hoping there was a way to fix this problem without running ground wires all over the layout.  While reading more about the ground plane issue, I stumbled upon this passage posted by OGR forum contributor DaleH:

The signal that is sent down the track by the single wire IS NOT received by the antenna in the locomotive. That signal is conducted through the wheels of the locomotive to one "end" of the receiving circuit. The other "end" of the receiving circuit is connected to the antenna, and the antenna picks up an airborne radio signal that radiates from the wiring of the house.
The radiated signal starts as the "ground" side of the TMCC/Legacy Command Base's output, flows through the Base's power plug and cord to the wall wart, transfers from the cable to the U-ground pin on the wall wart to the safety ground wiring of your house, and then throughout the house. This signal, usually referred to here as the "earth ground signal", permeates the entire area, and the antenna on the locomotive can pick this up.
The receiver in the locomotive is activated by the DIFFERENCE in the signals at the two "ends" because in order for any current to flow (in the receiver or elsewhere), there must be a voltage difference.
The systems works very well unless there is too much of the track signal present, making the antenna signal very weak. Common causes are overhead tracks, nearby metal structures connected to the track common (either directly or through leakage paths}, wire screen tunnels, or several parallel closely spaced track such as a yard. Usually problems can be resolved by connecting metal to earth ground, or adding an "earth ground plane" (metal, foil or just wire) near the problem area.
The misconception that the antenna picks up the track signal has been a major stumbling block to the common understanding of how to best use TMCC. To the best of my knowledge, Lionel has never published a truly accurate description of how the system really works.

Wow!  Nice detailed explanation.  I started considering all the things that could have affected my earth ground signal and the paragraph I marked in bold above did it for me.  I realized that my Lionel Legacy base was plugged in through a surge protector power strip.  I wondered if somehow this affected the ground pin on the power plug.  Sure enough, bypassing the power strip and plugging the Legacy base directly into the wall outlet solved all TMCC and Legacy layout problems for all locomotives WITHOUT running any ground wires!

I will assume problem solved...for now.