Dave Zucal posted:... It would make one think that running a subway set or a string of passenger cars, on a small layout, that you would totally loose command control. But you don't. Also, many layout are built with MTH's RealTrax that have lighted Lock-On's and lighted switch tracks...
The operative term is "running." From what I can tell, this choke meter is meant to be used with a non-running car. That is, the bulbs are NOT on when using this tool. I don't know what qualifies as common-knowledge, but incandescent bulbs have vastly different resistance when off and on - perhaps a 10-to-1 ratio from lighted to un-lighted. Sure, the tool could have been designed to test the DCS signal loading with the car lighted up but the circuit gets a bit more complicated.
Your comment about the lighted lock-ons is also spot on. Again, if you use this tool on an unpowered layout, the lock-on bulbs would be OFF. So the bulb filaments would be "cold" and the resistance would be much smaller than when the bulb is lighted.
Apparently, this tool is meant to determine if an incandescent passenger car is unduly loading the DCS signal. But expanding on your lock-on comment, a lot of guys add TVS protection devices to their DCS layouts. These "look like" a small capacitor. The math becomes a bit nerdy, but a typical TVS as recommended in various OGR threads has a capacitance of over 1000pF. At the tool's test frequency of 3.5 MHz a TVS "looks like" a passenger car in terms of how much in loads down the DCS signal! So to your point, we know there are guys who scatter multiple TVS devices around the layout (they are "cheap") and the layout continues to function with DCS in the same way that a train with a consist of stock (no added choke) lighted passenger cars functions with DCS.
Likewise, it's my understanding that some fast-acting circuit breakers (like the PSX) require a user-installed choke/inductor so as not to load down the DCS signal.
