I've set up an outdoor layout on the lawn for (a safely socially distanced) Thanksgiving. The layout is in the shape of the letter Y, with some switches, a short spur, and the connections for electrical power near the central intersection of the three branches of the Y. The two upper branches of the Y are 30 feet long +/- 10 feet, while the lower branch is 15 feet long +/- 5 feet. The track is about 80% Lionel tubular rail and 20% Lionel Fastrack. The track is laid "carpet central" (lawn central?) style, right on the grass. The track is pretty clean.
When I just have one leg of the Y connected to the central switches and power connections, TMCC works pretty well. It doesn't matter which leg of the Y I've connected--I've tried all three. However, as I connect more track, TMCC starts to work worse and worse, and eventually the locomotive just doesn't do anything. A similar effect is caused by lengthening the arms of the Y: when they're shorter, TMCC works better, but as I lengthen them, TMCC gets worse. When the TMCC doesn't work well, the lights on the locomotive flicker too.
The trouble is not dependent on where the locomotive is on the railroad. I could have the locomotive near the center of the Y, close to the Command Base, on clean rail, and the same effect is observed: as more track is added to the Y, TMCC becomes less and less responsive.
I know that the problem isn't the size of the transformer or electrical resistance. I put a conventional control locomotive on the railroad and it ran just fine all over. I also disconnected the Command Base from the railroad, and my TMCC locomotive works just fine in conventional control, and without any flickering of the lights. But, when I reconnected TMCC and wanted to run with TMCC again, it wouldn't work with the full railroad.
My current guess is that I have current leakage between the track and the lawn. This isn't a problem for conventional control operation, because the insulation between the center rail and the ties seems to be working pretty well. But, since the outer rails are directly on the grass, I think that maybe there is enough electrical contact to partially short out the TMCC signal between the outer rails and the earth ground of the grass. Or, to put it a different way, the contact between the track and lawn may be shorting out the isolation that the transformer provides between the outer rail "ground" and true earth ground.
To fix this, I'm going to roll out some food-storage plastic wrap and put it under the track to insulate it from the lawn. We'll see if this solves the problem.
If it doesn't, the next thing I will do is string out some ground-plane wire. Since the railroad is only going to be there for a day or two, I'd like to do it quick and easy. Can I just run some extension cords (I've got lots of them) parallel with the tracks, and plug the cords into a grounded outlet? That way the ground wire of the cords goes parallel with the tracks. Will having the hot and neutral wires of the extension cord near the track cause interference?
At the moment, I don't think that the absence of ground plane wires is the problem, because the TMCC works fine with smaller amounts of track in the same outdoor location. But I'll give it a try if needed.
A third idea in my mind is that I just have too much track form the Command Base to put a signal through, or perhaps my Command Base is defective. The Lionel manual says that you only need one Command Base for a layout, no matter how big the layout is.
I'd welcome your feedback and ideas! Thanks!