TMCC Signal Problem

["Ira Schneider" <ira_schneider@iname.com>]

I just spoke to Mike Reagan at Train America Studios (TAS) about our TMCC signal problem.

He gave me some insight about how the TMCC system works and what kind of things can cause
TMCC signal problems.  He also gave me some suggestions about how we might be able
to determine the cause of our signal loss:

1. Put a TMCC engine which experiences signal problems on the track.  Hold your hand about
    an inch over the top of the shell (i.e. above the antenna) and try to run the engine in
    command mode.  If the engine runs normally, the problem is that the antenna in the engine
    is too short.  This can be remedied by extending the antenna (i.e. adding a piece of wire
    to the antenna inside the engine's shell).

2. Both outside rails need to be connected to ground.  The TMCC system relies on the fact
    that the signal is broadcast from both rails and that the two signals reinforce themselves
    an inch or two above the track (where the antenna is in the TMCC engines).  If the signal
    is only being broadcast by a single rail, the signal may be too weak when it reaches
    the antenna.  The obvious solution is to ensure that ALL modules have both rails
    connected to the common ground and that both ground wires (i.e. in the 4-wire and 6-wire
    harnesses) are connected together.  We need to inspect all modules which are using
    K-Line shadow rail and make sure that both outside rails are connected to the ground
    wire (or or are jumpered together).

3. You are going to love this one!  The problem may be that the TMCC signal from one track
    is interfering with the signal from the adjacent track(s).  Since all four tracks are radiating
    the TMCC signals, and the signal path to any section of track may differ from the path
    to the adjacent track, the signals may be slightly out of phase.  If so, the signals may
    cancel each other out.  A solution to this problem is to install a ground plane between
    the adjacent tracks.  (A ground plane is simply a piece of wire (any gauge) connected
    to earth ground.)  We can test out this theory by temporarily running a wire
    between two tracks (where we have TMCC signal problems) and connecting the wire
    to earth ground.  If this fixes the problem, we need to find some way of permanently
    installing this ground plane on all modules.

We discussed various theories about what may be causing our problems and he said the
following are not likely to be causing the problem:

1. MTH DCS system.  This system was designed to be operated in parallel with TMCC
    and should not cause any TMCC signal degradation.

2. Metal bridge on track 3.  Rick's bridge is not likely to disrupt the TMCC signal.  If
    anything, this bridge could be a perfect ground plane if it was connected to earth
    ground.  It would isolate the TMCC signal on track 3 from tracks 2 and 4.  Of course,
    it is only a short bridge, so it wouldn't help the overall problem.

He also said that the TAS TMCC Signal Doubler was actually designed for 2-rail operation.
It superimposes the TMCC signal on both rails to mimic the 3-rail systems.  He only
recommends using the Signal Doubler on 3-rail systems if there are large sections of
the layout where one of the outside rails is insulated to provide train detection.  In this case,
the Signal Doubler would send the signal along both the outside rail and the center rail,
again mimicing normal 3-rail operation.  In our case, he doesn't think the Signal Doubler
would help.

We know that our layout used to operating TMCC engines flawlessly.  Over the years, TMCC
operation has degraded.  In the past few years, we have been using more and more K-Line shadow rail for
new and refurbished modules.  We have also added the MTH DCS system (which is only
connected to tracks 2 and 3).  I still suspect that the main problem with the TMCC signal is
the lack of continuity of the ground signal across the K-Line shadow rail tracks.

Since we are set up at The Railyard, we can experiment with some of this stuff.  I will bring some wire
with me on Saturday and we can try out some of his suggestions.  If you are coming to The Railyard
on Saturday and have a TMCC engine which has been running poorly (or not at all) on our layout,
please bring it so we have something to test with.

Thanks.


Ira