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G, I remember reading on the forum that the TIU transmits its signal to the engine via the center rail and that the engine responds to the TIU via an outside rail. Is that true?

Dave Zucal posted:

G, I remember reading on the forum that the TIU transmits its signal to the engine via the center rail and that the engine responds to the TIU via an outside rail. Is that true?

Everything is center rail + outside rails -. The engine and tiu are just on different time slices

What he said.   The track and wiring to the TIU is just a transmission line, and it takes both wires to send the signal back and forth.

Thank you guys. The reason I asked is because when laying track we're told to avoid creating a continuous loop so that we don't have signal collision. If both rails are used, why don't we also avoid loops with the outside rails? If track blocks were totally isolated from each other, would we have better signal communication between the TIU and engine?

Dave Zucal posted:

Thank you guys. The reason I asked is because when laying track we're told to avoid creating a continuous loop so that we don't have signal collision. If both rails are used, why don't we also avoid loops with the outside rails? If track blocks were totally isolated from each other, would we have better signal communication between the TIU and engine?

It's from transmission line theory like GRJ said.

When you transmit into a loop there's two forward propagating wave-fronts that create an interference pattern with nulls (spots with no signal). If you break one rail of the two (IE the center rail) around the loop then the wave can't propagate through it in both directions and it doesn't really matter if you break the ground or not. For a more analytical explanation maybe browse : Transients on TLines

Last edited by Adrian!

Thanks Adrian. That PDF is helpful in grasping how it all works. I would also tend to think another possible reason that lighted passenger cars cause us signal problems could be from the fact a mini loop is created when the two hot wires are connected together within the car or should we not be concerned with that loop?

Dave Zucal posted:

Thanks Adrian. That PDF is helpful in grasping how it all works. I would also tend to think another possible reason that lighted passenger cars cause us signal problems could be from the fact a mini loop is created when the two hot wires are connected together within the car or should we not be concerned with that loop?

Uh a good rule of thumb is 1/10 lambda is where the wave propagation behavior start to appear. DCS is a 3 MHz square-wave so that’s like 10MHz bandwidth with harmonics considered. That’s a 30 meter wavelength so 3 meters or about 9ft diameter is where the loops would start to have an effect. Seemingly a lot bigger than the passenger car.

Thanks again Adrian. I've always wondered about that mini loop.

Dave Zucal posted:

Thanks Adrian. That PDF is helpful in grasping how it all works. I would also tend to think another possible reason that lighted passenger cars cause us signal problems could be from the fact a mini loop is created when the two hot wires are connected together within the car or should we not be concerned with that loop?

Actually, I think it's more likely that the car includes some active components that are blocking the DCS signal.  Any significant capacitance across the track power will cause degradation of the DCS signal.  All my electronic modules use a 22uh RF choke in series with the track power connection to eliminate DCS issues.

There are still some TIU Port Tester kits available. Contact me by email (in my profile) if anyone is interested.

I use mine a lot, it's a great quick check on the health of any TIU that comes through for repair.

How do I contact rtr12 to buy a TIU channel tester?

Ferrantino posted:

How do I contact rtr12 to buy a TIU channel tester?

Oh, I don't know.  Maybe look in his User Profile and send email to his address like everyone else does?

Yes, GRJ has it, that will work just fine.  As he says, my email is in my profile.

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