TMCC Signal Problems & Hardware Cloth

Personally, I think I'd be inclined to add a couple of wires that could be connected or left free.  Since I'm assuming that the installation of the chicken wire would be somewhat permanent, if it didn't have the desired effect, it would be difficult to remove it.  OTOH, a couple of wires could be left unconnected and not affect things nearly as much.

Doing TMCC with multi-levels is still somewhat of a "black art" with large layouts, it'll be interesting to see what folks like the NJ Hi-Railers have to say, they're still tinkering with their configuration with TMCC.

I'm actually doing just that as I build my second level. I have already experienced signal issues on some of the completed sections of the layout.

The chicken wire can be seen on the left side of this picture. It is in direct contact with grounded electrical boxes which are providing lighting. It will be a while before this system can be tested. I wish I could provide a definitive answer on this, but like John said this is a "black art".

I have several mountains with chicken wire.  No issues with signal.  If a signal issue shows up with your layout, I would go for an earth ground wire to your chicken wire.

Whenever I've had a weak TMCC signal with upper and lower levels I go to the weak signal area and jump a wire from the lower outside rail to the upper outside rail directly above it. Works every time.

romiller

That's a very interesting solution. After watching Mike Reagan's video a number of times, I see why that would work. The trouble arises from there being too much signal, or rather multiple signals that are not synchronized, thus they confuse the receiver. The earth ground shield method allows the unsynchronized signals to coexist but not interfere with each other.

Everything I read suggests that you wait and see if there is a problem then try a remedy.  You may put in a lot of chicken wire for no reason.  All IMO; Don

I'm confused about the reasoning of connecting jumpers between the outside tracks.  Since the wavelength of 455khz is 2161.69 feet, I can't imagine this having much effect.  Normally, when you have multiple levels, the signal that is weak is the earth ground, not the track signal that is above and below you.

Nothing scientific but I know Radio Frequency's do strange things. Don

Don, for my large layout, an ounce of prevention is worth a pound of cure. It is a lot easier to install during construction than to retrofit later.

John, it's not the 455khz signal itself, it's the 60hz carrier that is out of sync. At least that's my understanding from Mike's video. The relevant part starts at about 6 minutes in.

http://www.youtube.com/watch?v=UQ-hiIvPxVs

So when Romiller bridges the two ground rails from different tracks, he forces them back into sync.

I'm sorry that I don't believe much in that video about the signal propagation.  If the antenna is receiving the track signal, why the emphasis on the earth ground, and why does laying a true ground wire over the tracks solve the signal issues?

In truth, the antenna really receives the earth "common" side of the signal, the locomotive frame and trucks receives the track side of the signal.  Most of my electrical engineering was spent on the digital side of the fence, but I remember enough of the RF theory and operation to know that explanation is flawed.

Dale Manquen has a pretty detailed analysis of how TMCC function on his website.  TMCC Signal Basics @ TrainFacts

I'll just post the pertinent section.

The antenna connects through a wire to the input stage of the radio receiver. As we saw earlier, we also need a second half to the antenna system so that we can get current to flow through the receiver. For this application we use the frame of the locomotive as our ground reference. The received radio signal will flow between the antenna and the frame of the locomotive. Note that the frame is also connected to the wheels and hence the track outer rails. That means that our receiver is sensing the current flow between the antenna and the outer rails.

We must stop here to dispel Myth Number 1 – “The antenna on a TMCC locomotive picks up the Track signal.” As we just concluded, one side of the receiver’s input connects directly to the outer rail, and hence the Track signal. If the antenna also picked up the same signal, there would be no voltage difference and no resulting current flow. The antenna IS NOT PICKING UP THE TRACK SIGNAL. If not the Track signal, then what is the antenna receiving?

Click on the link above for the complete description of the signal propagation.

The problems I had were with tracks running parallel in close proximity such as yards etc. Between levels not so much but my upper level is 12 plus inches apart.

I did re-read Dale's article. So, there two parts to the signal, the radio signal which goes out through the outside rails, and the earth ground which the antenna picks up to complete the circuit.

When we add extra sources of earth ground, such as the chicken wire, we are trying to ensure maximum signal to the antenna side of the equation.

But what about the rail side of the equation? Somewhere in that 455khz signal has to be the information that tells the train what to do. If that data isn't clear, all the earth ground in the world isn't going to fix it. Could this be what Mike is trying to explain in the video?

Think of the radio signal in terms of an AC power cord.  There has to be two conductors to complete the circuit.  The same applies to the RF signal, the track signal and the antenna picking up the earth ground side of the signal complete the circuit.

I'm not sure what Mike is trying to explain in the video, but the one obvious error is the antenna does not receive the track signal directly.  I didn't hear mention of the earth ground at all in the explanation, hence my doubt of it's accuracy in regard to the role played by the antenna.

I agree that adding the earth ground to the chicken wire would be called for if you had a weak signal issue, since that's usually the side of the signal that is problematic.

I get that part John, but with any radio signal, there are two issues. It is the difference between hearing and listening.

You're driving down the road, with your AM radio on, and you go into a tunnel. We all know what happens, no reception. The signal is blocked by anything above the receiver.

Now you're driving down the road, and a second station starts broadcasting on the same frequency. Of course in the real world the FCC tries to ensure that this doesn't happen. You get two sets of information, and it is hard to listen to either one.

It is not just about receiving the signal, it is also about the information the signal contains. I think this is what Mike getting at when he discusses different loop lengths and parallel tracks. You may have perfect reception with garbled message, which also results in failure.

With TMCC, it is difficult to identify which problem is present. By adding metal elements tied to an earth ground source, we can effectively block unwanted cross talk as well as providing enhanced reception.

I'm not sure what that video was trying to explain, but IMO it didn't do it all that clearly or correctly.

Many folks, including our modular club, run with just one outside rail, the other being allocated for block signals.  This has had no effect on the TMCC AFAIK, the Legacy works fine across the entire layout, including long legs that stretch over 50 feet in one direction and the yards with half a dozen sets of tracks.  I don't doubt that having both outside rails common would possibly be of benefit, the place where I see that being helpful is small motorized units with one traction tire, they only have one live wheel connection if they're going in a certain direction on the track.

As I previously mentioned, the wavelength of the 455khz being almost half a mile long, limits multi-path issues unless you have a really huge length of track. The command is sent out at the zero crossing of the 60hz, but it's modulation frequency is only 455khz with that long wavelength.

I often wonder if the problems that the folks at NJ Hi-Railers have with TMCC could be caused by multi-path distortion, but I'm not sure how you'd prove that.

I too use only one outside rail for TMCC, but have been adding those .1uf capacitors that were also mentioned in the video in the hope of improving performance.

Then there's our old friend the unshielded inductor, inside the engine, that loves to mess with signal. We had that lengthy discussion (almost a year ago), then Mike chimed in and nailed it. I still have a bunch of those to deal with.

I did place my base as close to the center of the 40' x 50' room as possible. I hear that would be more important for DCS (which I won't be using).

All I ever wanted was reliable operation. There are days when I envy those who use DCC.

I guess the bottom line is that because TMCC uses a radio signal to control trains, it is subject to a variety of types of interference, any one of which can cause the system to not work properly.

The capacitors are not a bad idea if you want the signal across both legs, and they won't interfere with the signaling aspects of the isolated rail.

I'm also enclosing the RS4 power supply inductors as I run across a problem engine.

Are you just making covers and tying them to the ground trace, for those inductors?

Actually, I got some dead RS power supplies from Marty and I'm using the covers from them on the good boards without the covers.