Earth Ground

If you are referring to a Post War transformer, it is not advisable to ground the output of the transformer.  This is a safety issue, and technically is prohibited by the NEC.

There is no reason to ground your transformer!

Who ever made it has seen to the safety issues already, and so grounding a transformer defeats it's purpose as well as being against the NEC regulations.

If it is an older transformer such as a post war ZW, you can add in TVS units after the power terminal outputs so as to protect your modern electronics in the engines.

A good rating for a TVS is 32 volts and bi-directional.

Mouser Electronics has a good supply of these and at reasonable prices.

Lee Fritz

Besides, if you ground the U terminal of the transformer, your TMCC/Legacy stuff will most certainly stop working!

I thought this might be the case.  What is the technical reason for the Legacy/TMCC not working if U is grounded?

The track signal goes out on the U (common) pin, and the other side of the signal is connected to earth ground via the 3'rd pin on the power brick.  If you ground the U terminal, you short the TMCC/Legacy 455khz signal.

Thanks for the explanation.  My power brick has a 2 prong polarized plug. Based on your explanation I assume earlier bricks had the 3 prong plug.  I ask because I want to be sure I understand your comment about the "3rd" pin.

It's the Legacy or TMCC base that has the 3rd pin, that's where the signal originates.  I don't know of any Lionel transformer that comes standard with a three-wire plug, maybe new ZWL, never looked at the power plug, but I doubt even that one would.

I apologize for being slow on the uptake here, but am new to this and do want to develop a better understanding of how things work.  

When you state: "the other side of the signal is connected to earth ground via the 3'rd pin on the power brick", I'm just not getting what the "3rd pin" on the power  brick is.  My power brick has a 2 conductor cable coming out of it with a polarized plug on the end - there is no 3rd pin.  My legacy base has the single U post on it along with the power socket.

Thanks for sticking with me on this.

Look at the Legacy base power supply.  Unless someone has hacked it off, it has a three-prong plug for the AC power.  The 3rd prong on the power plug is how the "ground" signal gets impressed onto the house wiring, that's the signal that the TMCC antenna actually picks up.

Thanks so much!  Does Legacy work same way or is the signal pitched up off the U tracks?

TMCC and Legacy have exactly the same signal scheme, Legacy has different content on the carrier, but it gets to the devices the exact same way.

Interesting, using 455kHz signal.  As I recall that is the IF frequency output of the mixer tube/transistor used in superhetrodyne receivers (and if you know what I am talking about, you know how old I am!)

That's probably why you can "hear" the TMCC signal on an AM radio.

Yep, I was amused that they picked 455khz, it is a familiar number.

You actually shouldn't be able to hear the signal on an AM radio, but you can on the low end of the dial.  It's interesting to try to pick out the different functions as sounds.

I do know what you are talking about!  I still have in my scrap box a couple of old can-shielded 455-KHz IF transformers.  I was hoping I might find a use for them some day.

Build a TMCC system?

TMCC uses 455kHz probably because there's inexpensive off-the-shelf IC's based around the IF frequency. Here's the description of the MC3372 chip that's used in the R2LC.

"Low power narrowband FM IF.

The MC3372 performs single conversion FM reception and consists of an oscillator, mixer, limiting IF amplifier, quadrature discriminator, active filter, squelch switch, and meter drive circuitry. This device is designed for use in FM dual conversion communication equipment.It is designed for use with either 455 kHZ ceramic discriminator or parallel LC components."

Hey, did you notice the part about the meter drive? It can be used to show signal strength. Has anybody hooked up a meter to pin 13 of this chip to show signal strength on their layout?