We ran the TMCC antenna extension wire the full length of the upper level, one continuous wire, plugged into the green ground hole in a wall plug. Used 24 gauge wire. Hot-glued it to the side of the sub-roadbed, so it radiates the signal down to the lower tracks. Works GREAT!
Didn't need one in the six-track yard, or anywhere else on the layout.
No TMCC signal problems at all anywhere.
DCS didn't care .. continues to work fine.
The wire is on the edge of the upper level in the photo.
