Our layout at the club is ~30' X 200" and we had issues with our TMCC/Legacy signal. The only way we were able to start addressing the issues was to take measurement readings of the two portions of the 455kHZ signal (the earth ground/air link portion & the "U" terminal connection from the command base) so when changes are made on the layout, we knew if we were improving the signal.
455kHz Earth Ground Signal Strength Meter -The first piece of test equipment built was the 455kHz Earth Ground Signal Strength Meter, which information above was posted on how to build. (I will also provide another post on this item in the TMCC/Legacy section so it will be easier for members to find in the future). As we were using the 455kH earth ground meter and going through the various 455kHZ remedies which are also listed above, we saw what worked and what didn't on the layout. As we went through the various remedies and checking results on the meter, we found this was a lot easier than trying to figure out if the engine head light is blinking more or less. Using the meter in my option is the only way to to get a handle on the this portion of the signal. Thanks to OGR forum member Gary Emmich who initially found out that the R2LC board has signal strength measurement capabilities.
Testing Command Base unit "U Terminal - The other very valuable piece of test equipment is an oscilloscope. I used this to measure the portion of the 455kHZ signal coming off the command base "U" terminal. I would first take readings on a small set loop, so you know what the signal should look like under ideal conditions and get a voltage reading which should be in the neighbor hood of ~5 vpp. If you don't have an oscilloscope see if you can borrow one or they can be purchased for under $400, which is much less than the price of what engines are going for today! If you can't get a hold of an oscilloscope, then check out Dale Manquen post on measuring the signal output of the Command Base "U" terminal.
The "U" terminal reading is VERY important and should be the VERY first item you test before doing anything! You want to make sure the command base unit "U" terminal connection is working correctly before trying to address potential layout issues.
Come and visit us at Trainstock 8 and you can see the equipment discussed above and talk to the TMCC/Legacy team Chris, Jim and myself.