TMCC Signal Strength

Based on what I have learned about TMCC, the signal is being transmitted from the outside rail of Track 1 (upper deck) and received by the built in antenna in the locomotive below.  So, yes, that would seem possible.

Wrong.   The signal on the outside track is conducted directly to the locomotive electronics by the wheels.  The antenna is to pick up the other half of the signal from the earth ground.  Ground the antenna to the frame and you'll find that TMCC ceases to work.

 

The issue posted by the original thread starter is just random coupling between the two tracks, or there is a common connection somewhere.

Thanks gunrunnerjohn!  Don't mean to hijack this thread but, curious.  If one connector connects to the outside rail from the base, where is it picking up earth ground from? An in depth explanation may help us correct our problem we are having on a large layout with Legacy.  See the thread, Legacy problem on Big Layout. 

 

Sorry John but you have it completely wrong.  TMCC does not rely on any wheel to track contact.  If you don't believe it, try this experiment. 

 

Take a TMCC command base and attach it to a length of wire.  Lay that wire on the floor.  I used an orange wire in the photo below.  Put a length of track on the floor next to the wire but not touching it in any way.  Connect that track to a transformer.  I used alligator clips.

 

 

Plug in the command base and the transformer.  Place a TMCC loco on the track and apply voltage.  Grab a Cab-1 and enjoy full TMCC control.  With the command base on, the loco will not run conventionally if you cycle the transformer power.

 

I routinely turn on my layout, then run a TMCC locomotive on my work table with a separate transformer alligator clipped to it.  I have full control with my Cab-1 even though the table is at least 6 feet from the layout.  The track is simply the TMCC broadcast antenna.  The locomotive does not need to touch this antenna.

 

BANDOB has observed this fact on his own layout, too.

 

Digistew, the command base broadcasts the other half of the signal back through the grounded plug in its wall wart to the ground wire in the building wiring.  In my basement, I have several house wires and copper water pipes in the ceiling over most of the layout.  TMCC has always worked great in those areas.  On one side of the layout, there are no house wires or copper water pipes above the layout.  TMCC operation was very spotty on that side until I added several "ground plane" wires.  If your layout is in a metal building, can you connect earth ground to the metal of the building?

Bob, Thanks for sharing this information.  Yes, we could attach to the building and perhaps even run wires up overhead.  Not sure of the ceiling height (Pole Building) I would guess 15 - 20ft.  Would that still work?  You must have read my thread because it does work if we put wires directly over the track.  However, we have Not tried to put them up near the ceiling or use the existing metal ceiling.  You might be on to something here!  Thanks!! 

Not sure that the distance per se is the issue.  A single wavelength of the track signal is almost a half mile long.  The main problem with the signal propagation is that any large ungrounded metal object can become a secondary radiator. TMCC operates deep in the near field and the magnetic component of the initial transmitted signal will induce a secondary signal from these objects. This secondary signal can often times be of a greater strength than the original.  These secondary radiators can interfere with the receivers ability to see the reference plane (aka the side of the signal on the house wiring).  

 

If you have a poor earth ground on the house/house wiring you may want to consider a) using Dale M's technique of pulling the reference plane off of pin 5 of the serial port on the command base.  This is about as direct a connect you can get to the other half of the transmitter's output.  b) Consider abandoning the third prong on the command base power supply and install a cheater between the command base and the wall.  User the lug on the cheater as the contact point for "the other half" of the dipole and make an "antenna" out of an ungrounded metal tube.  I suggest a vertical position (aka 90 degrees from the track plane) and as near as possible to the center of the layout as you can get.   The objective is to set up the two poles of the transmitter so that the receivers antenna in the loco is sandwiched between them.  In "normal" operation the house wiring envelope does this.

" The main problem with the signal propagation is that any large ungrounded metal object can become a secondary radiator."

 

I wonder if that is what is happening on my layout. If you note the video, there are metal fences on each side of the upper level bridge. There is also a string of lights mounted under the bridge, with the wire looping back and forth under the tracks to which the Command Base is attached.  Also, underneath the lower level  of the layout, are several metal file cabinets on coasters. Could and/or all of these be secondary radiators of the signal?

 

Not to mention the metal shelving along the basement wall, also on coasters.

 

 

If you get good signal everywhere but a few "spots" than there is something in that area that is interfering with the receivers ability to discriminate the track signal from noise.  As Dale has noted, in these cases puling a wire off of pin 5 and running that near the track is probably the easiest way clear/clean it up.  If you are having over all problems then the situation is more serious/difficult to deal with.  

 

The system was meant to be used on smaller layouts in HOMES with proper wiring.  The assumption being the house has little or no structural metal components.  The house has three wire circuits with the ground wires tied together in the load center and that's bonded to earth ground.  The soil in the area is actually moist enough to get a good ground.   The wiring follows typical HOUSE wiring standards and it does create an envelope that basically surrounds the layout.  As you drop these parameters the system's behavior can become problematic.

Well, I have a detail wrong, hardly completely wrong.  True, since the frame of the locomotive and the track both have mass, physical contact is not necessary.  However, the two components of the signal are as I described.

I have noticed that all engines start up in TMCC just with the base turned on and no connection to the outside rail. Once I upgraded to Legacy,  this no longer happens.

Hello all, tonight I tried to reproduce Bob B's observations. I put a piece of long straight on the workbench. Connected it to an RW, plugged into a different outlet than the one for the main layout, Command Post, etc. Put B&O GP 9 #5616 on the track, turned on the power. Nothing happened until I addressed the locomotive with the cab 1. Then it was under TMCC control. See video.

 

Now, I know absolutely the two lines are not connected physically, except through the house wiring.  I still don't understand gunrunnerjohn's comment: "random coupling between the two tracks." 

 

But, these experiments indicate to me that I MIGHT be able to run my TMCC locomotives on my lower level module at shows, using the signal from the main layout. I'll just need to be careful about having the same number as a TMCC locomotive on the main. I'll try it on Dec. 22 and post what happens. 

 

 

 

 Who's got the popcorn????

I'm not sure why this should be a problem, other than possibly needing a ground wire running under the upper level deck.  You can connect the common for the outside tracks between the two decks, right?

Yes, it will be easy to connect the two outside rails if I need to do that.  I don't seem to need to do it at home, but might be a different story in a large area like the B&O Museum Roundhouse.

I suspect it wouldn't hurt for reliability, what's the harm?

Here's the report on the set-up at the B&O Museum. TMCC locomotives ran fine on the lower level of the module, even without a wire connecting the outside rails.  Here's GG1 4907 happily rollling around the lower level, under TMCC control. 

Thanks for posting the outcome, also nice to see a GG1 running!  I havn't seen one of those run in over 40 years.