MTH Track Signal Question

Common issue with some lighted passenger cars.  The addition of a 22uh choke in each passenger car pickup lead will usually solve this issue.  Here's a suitable 22uh 1/2A RF Choke.

Make sure you are still getting 18 v with the cars on too.

 

Thanks John.  I'll be looking into that.

Thanks Dave...........maybe I am mistaken but does voltage have anything to do with signal strength?

Dave

Voltage by itself shouldn't have a significant impact on signal strength AFAIK.  The lighted passenger car issue has been discussed a few times before here, that's why I include the 22uh choke in my passenger car lighting modules.

Soo Line posted:

Hello Gents

I'm running with MTH TIU - Rev L.  -  Version on TIU and Remote are 6.00

When I run an MTH engine around the layout in track signal mode.......I have 10s.

When I run the engine around with two lighted passenger cars.....I get all kinds of readings from 4 to 10.

Why do the lighted cars seem to affect the track signal strength?

Thanks

Dave

 

 

 

gunrunnerjohn posted:

Common issue with some lighted passenger cars.  The addition of a 22uh choke in each passenger car pickup lead will usually solve this issue.  Here's a suitable 22uh 1/2A RF Choke.

Does this apply to conventional lighting only?

It's specifically for passenger cars that affect the DCS command signal. 

Dave, what make cars.  I have done a few posts over the years on what passenger cars will hurt signal.    When this issue was showing up, Scott Madd and Mike Reagan had me test the newer boards they were going to use.  I did a lot of testing on all boards and came up with the afore mentioned 22uh choke that fixed issues.  I was buying them by the hundreds.

Marty

MTH Premier Passenger cars  ............  20-66118

Thanks

Dave

That's hilarious!

Is there some new electronics person at MTH making changes?

 

Did you do the track signal test running or stationary?  The information indicates best to test signal strength stationary.  Is this correct?

I've done the tests running - slow - and stationary and get the same results.  All 10s without lighted cars in tow.

Dave

Soo Line posted:

Thanks Dave...........maybe I am mistaken but does voltage have anything to do with signal strength?

Dave

Dave,

The performance will definitely be degraded if the voltage is too low.  Incandescent lights rob you of voltage.

Dave

The track voltage, if drawn down too low, will impede the DCS electronics in the engine from effectively responding to DCS commands. This can cause a perceived degradation in the DCS signal.

Should chokes be added for LED lit passenger cars too, or just incandescent?

This is not good news as I am planning on running more passenger trains this fall. What can I expect? Lost signal strength by itself is not a problem that can't  be dealt with.

Not to worry! I ran my own test tonight and still had 10's. But it's good to have this information about passenger cars. Thanks 

Dave Zucal posted:

Should chokes be added for LED lit passenger cars too, or just incandescent?

Since many LED cars have a capacitor for flicker prevention, those most certainly should have a choke to prevent degradation of the DCS signal.  My LED lighting modules have included the choke from the first one shipped.

 

Soo Line posted:

I've done the tests running - slow - and stationary and get the same results.  All 10s without lighted cars in tow.

 Hard to believe it's anything other than the lighting interfering with the DCS signal.

t's the CV board that's the problem, not the lights that it supports.

FWIW  I don't have any passenger cars with LED lights. There were more than twenty lit when I ran my test.

Barry Broskowitz posted:

 Hard to believe it's anything other than the lighting interfering with the DCS signal.

t's the CV board that's the problem, not the lights that it supports.

Barry, don't be so obtuse!  The CV board supports the lights and is certainly part of the lighting!

John,

don't be so obtuse!

Really?

If you turn off the lights, does the problem go away? If you remove the lights, does the problem go away?

If the answer to both questions is "no", it would seem to me that it's the board, not the lights.

Right Barry, and you'd take all the bulbs out and leave a then useless board for what reason?  Get a grip.

Let's put it another way, since you are having trouble with simple concepts.  If I add the 22uh choke to the power pickup, does it matter what part of the lighting causes the issue since it will be cured?  Did adding the choke solve his problem?  If so, what does your nit-picking add to the conversation, other than making you feel good you got your 2-cents in?

Yes, if you turn off the lights it will go away as the light switch is before the constant voltage regulator.

John,

If you remove the lights, does the problem go away?

The answer is "no". Further, is the only possible use for a CV board for lighting?

Let me be clear and use small words so you're sure to understand: The board is the culprit, no matter what is it's purpose. The lights are just along for the ride.

Get a grip.

Really? How about if I suggested what you could grip...

Barry, after all your BS, the solution is still the same as I initially suggested, add the 22uh choke. Of course, I was just trying to solve his problem, not prove how intelligent I can sound.

Feel free to have the last word, I'm sure it'll be really profound.

As I originally stated,"It's the CV board that's the problem, not the lights that it supports."

gunrunnerjohn posted:

Common issue with some lighted passenger cars.  The addition of a 22uh choke in each passenger car pickup lead will usually solve this issue.  Here's a suitable 22uh 1/2A RF Choke.

This is a correct approach that John has suggested!... I do it too and it works well.

This is why:

 

Why the choke works:

The TIU has an output impedance of an ohm or two at 3.25 MHZ (the DCS spread bandwidth). Lets just call it ZTIU....  Each passenger car (CV board, light, whatever...) is connected across the rails puts some parallel Z on the track. So the voltage the locomotive PS board sees is like:

(Z1||Z2||Z3+...) / [(Z1||Z2||Z3+...)+ZTIU]

So as you put more and more Zns the numerator (and your voltage gets smaller).It's a voltage divider.  A choke/inductor is like a resistor with a frequency dependent impedance (ignoring a discussion of phase for now) so as the frequency goes up the impedance goes up.

ZL = 2(pi)(freq)(inductance)

If you pick a large enough value like 22uH the 60 Hz current can still flow into the passenger car becasue it's only

2(3.14)(60)(22e-6)= 0.08 ohms (so basically a short)

But at DCS frequencies its like

2(3.14)(3.25e6)(22e-6)= 449 ohms (so much much larger than the TIU output)

 

Essentially the passenger car still loads the track but only at the 60 Hz frequency not at the DCS frequency.

 

-->At the 60 Hz power the TIU sees a load of (Passenger Car Resistance) + 0.08 ohms

-->but at DCS frequencies it sees a load of (Passenger Car Resistance) + 449 ohms

 

It's a basic simple and elegant circuit answer.