Need Help/Advice with TMCC Outdoors

This isn't going to be much help if it's true, but some TMCC command bases and handhelds have been found to have poor radio frequency communication due to being slightly off frequency.  I suspect a weak RF link might explain what you're seeing.  There is a way of adjusting the frequency but it's beyond my abilities to tell you how. 

I've heard that the TMCC signal can be effected when it touches the ground. If the grass or ballast the rails are on is wet for example, the signal will suffer. I've also heard that putting the signal on an overhead wire like scale telephone poles, helps eliminate this issue.

I've never tried TMCC outside and this is all hearsay!

The antenna that transmits the signal to the engines is the ground wire in the house. So it stands to reason that you might run out of range outside. Running a cord outside over head, preferably, would probably work to put the ground wire antenna over the layout. The common and hot wire will not affect the use of the ground wire overhead.

Thanks Chuck.

I did do a test where I ran a wire with TMCC connected laying next to the track but not connected. The engine responded well to commands.

I never went further than that.

@cjack posted:

The antenna that transmits the signal to the engines is the ground wire in the house. So it stands to reason that you might run out of range outside. Running a cord outside over head, preferably, would probably work to put the ground wire antenna over the layout. The common and hot wire will not affect the use of the ground wire overhead.

That wire is called "earth ground" for a reason, it's actually bonded to "earth ground" at the panel!  That being said, I suspect he has plenty of the antenna signal, the issue here sounds like excessive coupling between the "earth" and the track signal.

Note that newer command bases like the Lionel BASE1L or the Legacy command base have about double the signal amplitude of the old TMCC BASE1.  If you're working with the origional TMCC BASE1, it might be time to upgrade.

One effective way to get more signal is the TMCC Buffer.

TMCC/Legacy Track Signal Booster (Dale's Legacy Continues)

it would seem to me that pushing more signal would not fix the problem of the track sitting on damp ground. I believe lifting the track off the ground might be the easiest fix?

Actually, the lower impedance drive of the buffer would do a lot to overcome the coupling between the track rails and the ground.  However, you certainly have a valid point, putting even a small base under the track to remove any continuity between the track and the ground would certainly be called for!

The G&O garden railroad ran TMCC outside for years without problems.  We switched to Legacy several years ago.

The key to grounding both systems was to drive a grounding rod into the ground and connect it to the common on the transformer.  Our Z-4000 is in the a shed that is about 6 feet from the nearest track.

Another key is to make sure that both your engine wheels and the track is clean.  We always run a track cleaning car before running trains.  Outside the track may look clean but it usually is not.   I have had TMCC engines that would not run until I cleaned their wheels even though other TMCC and conventional engines did run on the same track.  

NH Joe

OK...the question here is what half of he signal is missing or compromised. Is the house wiring ground conductively coupled to the dirt earth outside enough to effect a significant capacitive short of the house wiring ground to the transformer U output (which is connected to the outside rails of the track which is setting on the ground). I think that is questionable, but running a house wiring ground wire over the track (or maybe near it somehow, but not on the ground) will prove something.

GRJ’s Dale M Booster is always welcome on any layout and may be the answer with a stronger signal with a lower source impedance if the track is truly effectively setting on the house wiring ground signal.

Also, New Haven Joe, what do you mean by “common” on the transformer? The U terminal? I don’t see how that would help, and might harm. If you mean the ground pin on the transformer plug, that might help but violates the wiring code having two ground rods, the one by the meter and the one you put in the ground. But the wire going from the transformer ac plug ground pin to the new ground rod might be enough ground wire signal to make a difference. I just would not use the ground rod. Maybe attach it to a stick near the layout.

I'm with you Chuck, I'm sure that's not exactly how it was done.  If you hook the track common to a large ground rod, I seriously doubt that you'd be getting any measurable TMCC signal, you're shorting the signal!

Hi everybody,

Thanks a lot for your replies. After I posted the topic yesterday, I set all the track on plastic wrap rolled out on the lawn, and that helped some. Also, by sheer dumb luck/coincidence/strange things happen/I don't know everything about TMCC, I switched the railsounds/signalsounds switch on my locomotive from railsounds to signalsounds, and that seemed to help it respond better. Any guesses as to why?

The locomotive worked pretty well for most of the day. We pushed all the track sections together to make sure that they were making good contact, and that seemed to help too. At the end of the day the locomotive started having trouble, but that may have been due to dew starting to condense on the tracks.

We cleaned the rail quite a bit, but we didn't clean the wheels on the locomotive. That's a good idea. I will do that (dew that, ha ha ha) and see if it helps.

We didn't try the extension cords strung out as ground wires, but I will probably try that later today.

I have a few questions:

From what I've read, I get the impression that the outer rails of the track and the U post are not connected to earth ground. This implies that the transformer is behaving as an isolation transformer. Is this right?

From what I understand, the TMCC signal is sent out through the ground pin in the power cord that goes to the Command Base, and gets propagated through wiring in your house. The antenna in the locomotive picks up this signal, and the current flow that is induced by this signal is returned through the wheels and outer rails to the U post and screw terminal on the Command Base. Is that right?

I'm slightly confused. Some people have advocated stringing out a wire connected to earth ground along the tracks. Other people say that if you connect a wire to the Command Base screw terminal and string out the wire along the tracks, the locomotive will pick that up. I believe these are two different electrical scenarios. Would they both work? Would they both work at the same time? Maybe it's even better at the same time! I need to get some Tylenol for my head after thinking about this....

Is there a good way to electrically join together two sections of tubular rail in a conductive, permanent way? Some sort of glue or clips or purpose-made gizmo perhaps? I'm thinking that I could permanently join together a number of sections of tubular rail in order to help the TMCC signal and cut down on voltage drops. Maybe I should just string out a bus wire and put some lock-ons on the rails farther out.

@Dan Parks posted:

I have a few questions:

From what I've read, I get the impression that the outer rails of the track and the U post are not connected to earth ground. This implies that the transformer is behaving as an isolation transformer. Is this right?

100% correct connecting the U post or outer rails to earth ground will insure you have no TMCC signal at all!

From what I understand, the TMCC signal is sent out through the ground pin in the power cord that goes to the Command Base, and gets propagated through wiring in your house. The antenna in the locomotive picks up this signal, and the current flow that is induced by this signal is returned through the wheels and outer rails to the U post and screw terminal on the Command Base. Is that right?

100% correct

I'm slightly confused. Some people have advocated stringing out a wire connected to earth ground along the tracks. Other people say that if you connect a wire to the Command Base screw terminal and string out the wire along the tracks, the locomotive will pick that up. I believe these are two different electrical scenarios. Would they both work? Would they both work at the same time? Maybe it's even better at the same time! I need to get some Tylenol for my head after thinking about this....

That's also correct, but in your case the earth ground is all around you, so that probably won't make any difference.

Is there a good way to electrically join together two sections of tubular rail in a conductive, permanent way? Some sort of glue or clips or purpose-made gizmo perhaps? I'm thinking that I could permanently join together a number of sections of tubular rail in order to help the TMCC signal and cut down on voltage drops. Maybe I should just string out a bus wire and put some lock-ons on the rails farther out.

A very good way to join as many sections of track as you like in a conductive, permanent way.  Short wire jumpers and solder!

Take a look at TMCC Signal Basics from the late Dale Manquen's website, a great treatment of TMCC operation and signal propagation.  That should set you straight by a guy that really understood the system in depth.

Hi John,

Thanks a lot for sharing that link, it was very interesting to read. A few things I learned are:

1. Neither the U-terminal nor the earth ground are left at 0 Volts DC by the Command Base. It inputs AC voltage to both the U-terminal/outer rails/wheels and to the earth ground in the wiring. The two signals add up. Is that right?
2. The orientation of the remote controller to the Command Base matters. I may have been holding it in the wrong orientation, increasing my frustrations.
3. He says not to power the layout with a coiled-up extension cord. Indeed, my extension cords were coiled on circular cord winder. I will try laying them out.

So, a follow-up question:

Am I correct in thinking that the antenna-based TMCC is much more complicated than simply running an electrical signal between the rails that could be read by an on-board decoder? Perhaps overly complicated? Was this done so that Lionel could have something to patent and profit on? Or is there a specific benefit to the TMCC approach? I believe that the digital signal sent through the rails is the idea behind DCS, but please correct me if I'm wrong.

Thanks!

Dan

Actually, it's a whole lot easier to build a reliable receiver for one-way communication like TMCC, evidenced by the far fewer issues getting signals distributed in a vast percentage of train layouts.  DCS, OTOH, with the bi-directional communication has some pretty tricky communication issues at times.

The other bonus is the TMCC signal lends itself to a fairly simple booster to aid signal strength, DCS would be very difficult to boost it's signal as you'd have to deal with each locomotive with the return signal.  Also, the two-way nature of it requires a far more complicated booster, and you really need to be able to tap into the TIU logic to know when to boost in what direction.

Both systems have their advocates, and each one has advantages and disadvantages.

If I'm called on to just show up at a layout and add command capability, I'd pick TMCC/Legacy, it's easier to get running regardless of the wiring on the layout.

In order to get DCS running on layouts, especially larger layouts, you have to drive sections from unique TIU channels that are isolated from other sections.  You also have to adhere to wiring practices to avoid signal reflections that scramble the track signal.  Obviously it's possible to do DCS on a large layout with good reliability, but it does take more care in the power wiring and power district planning.

Thanks for the insight, I appreciate it!

One other question for you:

I've been assuming that the two signals that the command base sends out--into the outer rails of the track and into the house ground wiring--are the same in amplitude but opposite in voltage at any instant in time. Perhaps that assumption is incorrect. If it is correct, then I'm confused about something:

The alternating voltage being applied to the outer rails should make it behave like an antenna too. The rails should be radiating out electromagnetic waves just like the ground wiring in the house is doing. And, that signal that the rails are broadcasting should be picked up by the antenna on the locomotive just like the electromagnetic signal broadcast by the ground wiring in the house. But, since the two signals are equal in magnitude but opposite in voltage at any given time, shouldn't they cancel out each-other's induced voltage in the antenna on the locomotive? But, in actual practice, this appears to not be the case. Why is that?

I have a guess at a resolution to my question: The rails are indeed broadcasting their own signal that is opposite to the signal from the ground wiring, and both signals are indeed picked up by the antenna on the locomotive. But, because the locomotive is also able to directly detect the voltage coming through the outer rails and wheels, it is able to take account of the effect of the signal from the rails, and deduce what the signal from the house ground wiring should be. But I'm not super sold on this guess.

I'd welcome your clarification!

The first few paragraphs of the description at the link: TMCC Signal Basics describes the link better than I will, so I'd suggest checking that out again.

It’s essentially like any circuit. Two sides to make a circuit. You can look at the rails as the common side of the RF signal while the “ground wire air side” of the signal is the “hot” side. The “hot” side is picked up by the antenna to the receiver in the engine. That’s why it’s best to have the “ground wire antenna” over the top of the engine...like the house wiring in the ceiling and walls. The receiver common side is connected to the rails.

This is my favorite Dale M drawing on this subject...

Lol, well I had to reread much more than the first few paragraphs, but indeed, I think I see the resolution to my confusion:

The outer rails and the earth ground wire are not two separate entities, but instead form the two halves of a dipole antenna. At the same time, the outer rails are doing double duty as the ground plane for the locomotive.

The whole setup is like if you had a dipole antenna transmitting to an AM radio in an automobile (which has its metal body insulated from earth ground by the rubber tires), except that to make this analogy accurate, you would need to connect a jumper cable from the car body to one side of the dipole antenna.

I guess another consequence of this is that the voltage difference between the outer rails and earth ground is cycling thousands of times per second if you have TMCC hooked up, whereas it would be constant or 0 if you were running in conventional control.

Does this sound right?

Thank you John and Chuck!

AAMOF, the waveform between the outside track and the earth ground will alternate at 455khz, the frequency of the TMCC carrier.  From a Legacy or BASE1L, the amplitude of the waveform will be between 5v P-P and 6v P-P.  For the older TMCC BASE1, the amplitude will be between 3v P-P and 4v P-P.  That's one reason that upgrading to Legacy helps many layouts, it's simply a stronger TMCC signal.

The TMCC Buffer is capable of boosting that TMCC signal to around 15v P-P, and also drives it with a low impedance amplifier to allow it to drive a lot more capacitance or lower resistance between the earth ground and outside tracks.  This makes TMCC possible in places like the New Jersey High Railers massive layout.

Another reason to have the TMCC Buffer is that it has an LED which reports low signal from the Base. I find that most useful since I have encountered a number of bases which have an out of spec low output. This problem has caused some owners to chase ground wire fixes instead of addressing the low output of the Base which they could not measure. The TMCC Buffer also provides a neat connection to access the earth ground signal wire.

You'll find that the TMCC Buffer shows no status LED for the TMCC base.  That indicates there's a TMCC signal there, and it's more than 2.5 volts, but less than about 4.5 volts peak-to-peak.