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

I only really follow in the fall through Christmas as my tree layout is the only space I currently have to set up trains.  

So it looks like while I was in "hibernation" this opportunity came and went.  Although the modest permanent layout I have planned eventually would likely not need this, I would have ordered one just to have.

So here's to hoping there may be a "second run" of this gadget at some point in the future.  I'm not the sort to get a kit and create it from that, so I'll have to wait for now.

Ok, as suggested by friends, take the Legacy System away from the layout for simple/specific testing, TaDa, it works....Then I added the Cab 1 to the Legacy System, they both work, tada. So, now that I know my command control works, I will check out the power on the layout....Now, Progress is being made.. So, I am using a ZW w/TPC’s 2 only 400’s each with 180 watt bricks. 

Ok, now, my system is up again, tada, reprogrammed the 2, ZW-C transformers, the TPC’s, everything seems to be working, Cab 1- Cab 2.... Tomorrow, after a thorough check out of all the wiring, I will install the DM TM Buffer....It just takes one step at a time, says my friend at the Madisonville Shops, to Win the race.  If I were to give this problem a Reason to go down, “the cause of the shut down”, probably a derailment occurred somewhere on the layout......Happy Railroading...

John, back on 9/10 I posted some info about the Legacy signal issue I was having on my 2 rail layout. I now have it fixed so I thought I would share the cause of the problem. You were correct it had to be some kind of ground loop issue. First just for info but not related to the problem, the layout power is supplied from a dedicated 20A circuit from the main panel. The house has 2 sub panels, one for inside circuits and one for exterior loads. The balance of the outlets and lights in the train room are supplied from the interior sub panel.

The layout was built with metal foil tape under all the track. All  the foil tape is connected together and wired back to the main control cart with a single ground wire. The problem was this wire was connected to a ground pin in a power strip rather than to the proper Legacy base connection. There are 3 power strips on the control cart, power strip "A" plugs into the 20A outlet, "B" plugs into "A" and "C" plugs into "B". The 990 base is plugged into power strip "C", The new Buffer is plugged into "A" and the separate ground pin mentioned above was plugged into "B".

As soon as I unplugged the separate ground connection the buffer indicator turned steady green, the layout works perfectly with all engines working everywhere on the layout. I will ultimately connect the ground wire correctly but I need to disassemble some cable bundles on the control cart to do that. I like it when a fix is that simple. I am really surprised a professional layout builder made this kind of incorrect wiring connection for a Legacy system. Also, none of the unique 2 rail controllers have any effect on the system function.


I see the foil as the problem. If you had just used a wire for an additional antenna to transmit the TMCC signal, there would not be such a large capacitive load from the ground wire antenna to the base (connected to the rails) end of the signal. I think terms like "ground plane", etc. are unfortunate in that they give a wrong impression of the purpose of the antenna wire in the house wiring or as an added antenna wire on parts of the layout that may be shielded from the house wiring. The term ground loop does not apply either. It's simply too much capacitive loading I think.


gunrunnerjohn posted:

One thing I might suggest it to "tone down" the buffer output somewhat, while still keeping a lot of the benefit of it being used.  Here's a simple way to "tune" the buffer output, see if this helps.  I'd start with my suggested values, this returns the amplitude of the TMCC signal to near default, but still allows you to have a lower impedance signal to help drive the TMCC problem areas.  You can then maybe change the resistors to 150 ohms each to give a small boost if the first one doesn't do enough for the TMCC.  The resistors should be 1/2 watt or larger.

TMCC Booster Voltage Divider

Adrian was talking about this, and I figured it would depend on exactly how the DCS was wired.  I suspect a perfectly optimum wiring of the DCS might not have the issue, but if you have any signal degradation of the DCS signal, it may be more adversely affected by the boosted TMCC signal.  Note that just because you got 10's for the signal test, that doesn't mean you have perfect DCS signal, it just means you have enough for solid communication with the locomotive.

Last time I was in civilization we had a good 10-12V DCS swing everywhere on the layout, but we were somewhere around 1/3 to 2/3 capacitive imbalance inner to outer rails meaning the 450KHz will show up across the DCS differential voltage at 1/3 of the amplitude it has to Earth ground.  I may try to hack the driver stage on your buffer to drop the voltage gain while maintaining the low output impedance.  

We had an accident on the launch line so we're being encouraged to scrub. I may be back working on this buffer sooner rather than later. 

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