Lionel Legacy Base Causing DCS Signal Problems - Resolved -

Just curious but have you test to see if the Legacy base works without the DCS on? I think you want to ensure that the Legacy base is working properly before going through any additional steps.

@Madockawando posted:

Just curious but have you test to see if the Legacy base works without the DCS on? I think you want to ensure that the Legacy base is working properly before going through any additional steps.

I haven't yet tested only the Legacy system by itself (I will try to do that tonight), but a couple months ago I was testing both DCS and Legacy together and the TMCC engines I have were running properly as far as I know.  If I remember correctly I was running both TMCC and MTH engines on the same section of track.  I don't have any Legacy engines to test, just TMCC.  Thanks.

Michael

I think you can use your TMCC engines to test to see if the Legacy base is working properly. My suggestion is to establish a baseline to ensure that both the DCS and legacy systems will work by themselves. If they do, then you can more to the next step and evaluate your layout to see how the interaction between the two may be causing interference.

We have the same issue at my club. Legacy/TMCC work perfectly separate but the legacy base kills DCSA Signal when powered up.

I have read of a few instances of this and it always seemed like the cause and the solution were usually different.

It would be great if we could get a complete list of all of the different causes that were found and what the individual solutions were.

I think my first step, based on what you've done so far, would be to borrow another Legacy command base and see if that makes a difference.  I have a 12 x 24 layout wired similarly to yours, and the Legacy system doesn't impact anything about the DCS.  However, we have seen this at Harry's house, and after rewiring for star connections instead of the big bus that was originally done it seems to be resolved.  I'm guessing that how the track is wired is probably a key factor.

The DCS Companion (3rd Ed.) lists various sources of low signal issues (including Legacy/TMCC) at pages 156-158, plus failure to follow initial wiring recommendations; like star wiring, separate blocks, etc.

Seems like that might make a good checklist to start eliminating potential sources, one-by-one.

Thank you everybody for the input so far!

I do have Barry's books and I believe I have followed the wiring principles from there.  My layout is star wired with isolated blocks using 14 Ga wire.  I followed his setup for adding Legacy/TMCC to DCS.  The only thing I didn't do was put an 18 volt light bulb like he suggested, but with just DCS I had a perfect 10 signal so I didn't think it was necessary.

Right now for testing purposes I only have 1 block of 1 loop hooked up.

Here is a link to my layout build with some pictures of my wiring for more clarification.

https://ogrforum.com/...suggestions-critique

GunrunnerJohn:  That is a good suggestion about switching Legacy bases to see if the problem resides in the base itself.

Also for clarification, the issue is occuring with no Lionel engines on the track, only MTH engines.

Thanks.

Michael

Before you go through the trouble of switching Legacy bases, have you tested the Legacy base that you have now by itself?

Madockawando:  No, not yet, but that is the first thing I will do before anything else, hopefully tonight if I have time. 

Michael

Good luck! Hopefully that test will help you bracket the problem.

Since the Legacy Base sends only the 455 KHz ("TrackLink" per Lionel's diagrams) signal to the track, there should be no conflict between the signals.  My club operates both systems with no problems other than initially adding an engine which requires a separate test track.

If, however, the Legacy Base is outputting RF outside of the 455KHz signal, perhaps a filter could clean up the output.  (I'll leave the filter spec. to the EEs on this forum).

Tracker,

If the Legacy Base is transmitting RF other than 455kHz then it's defective.  No need for filters.  It needs to be replaced.

M.H.M.

@Tracker John posted:

Since the Legacy Base sends only the 455 KHz ("TrackLink" per Lionel's diagrams) signal to the track, there should be no conflict between the signals.  My club operates both systems with no problems other than initially adding an engine which requires a separate test track.

Actually, it's been well demonstrated that the DCS and TMCC signals spectrum's can collide.  A guy smarter than I am did a lot of research on the issue.

Correlator Noise floor inflation by Legacy Signal Interfering with DCS

Ahah!  I missed Adrian's discussion when it was posted.

I hate my voice on this but maybe it will help here?

That's an interesting observation Joe.  That looks like the old TMCC base brick, is that what you're using?

Thank you again for all the info and input.  I had no idea this was such a widespread problem amd so much effort has been put into trying to diagnose and solve it.  Everything that has been shown here as well as on the other threads is exactly what I'm experiencing as well.  It is amazing that some people have both dcs and tmcc/legacy working flawlessly together and others of us have issues.  The million dollar question is what is the common variable or variables that either causes it to work or not. 

Has anyone tried putting the legacy base in a seperate room from the layout and running a long "one wire" cable back to the layout?  Or is there anything to do with the position of the legacy base (mounted vertically or horizontally etc) that affects the signal.

I didn't do any testing tonight. 

Very interesting discussion.  Hopefully we can land on something here that will help others with this issue.  Thanks again!

Michael

@gunrunnerjohn posted:

That's an interesting observation Joe.  That looks like the old TMCC base brick, is that what you're using?

yes

Although electrically challenged, it seems to me that the fundamental issue in these cases is that the DCS signal strength is being trampled upon by the Legacy/TMCC signal and this can be caused by a number of factors, including incorrect set-up of the DCS system, such as failure to use star wiring, block creation, etc.

If that is the given, once all the basic DCS set-up parameters have been eliminated as a possible cause, the solution would be to either increase the DCS signal strength (a "DCS buffer") or decrease the Legacy/TMCC signal. Since no one makes a DCS buffer that I know of, that leaves finding a way to decrease the Legacy/TMCC signal strength as a potential solution.

As the OP pointed out, one possible way to do that would be to increase the length that the "one wire" has to travel from the command base to connect to the track. However, I wouldn't do that by moving the command base to another room because that could potentially create over-the-air signal issues with the remote. You could add a signal boosting antenna to the base, but I think a better way would be to make a new, very long "one wire" and run it out of the room and then back (maybe 50' or so ?) before connecting to the track.   

Another way might be to attach the "one wire" to the input side of the TIU (I know, I know) rather than the output side, with the potential that the TIU's electronics would degrade the Legacy/TMCC signal enough to not stomp all over the DCS signal and still be strong enough to run  Legacy/TMCC equipment.

Just my random thoughts and maybe worth a shot.

Actually, the wavelength of the 455khz is over 2000 feet, and putting a long wire on it won't accomplish a thing.  If you really want to reduce the signal strength of the TMCC signal, a properly sized load resistor divider would be the way to go.  In order to know what you were doing, you'd really want to 'scope the signal.  Since the old TMCC BASE1 had a much lower amplitude signal, you could probably get away with chopping the Legacy base signal to about half it's amplitude.

Bad idea sending the TMCC signal through the TIU, that doesn't accomplish what you desire.

@greg773 posted:

We have the same issue at my club. Legacy/TMCC work perfectly separate but the legacy base kills DCSA Signal when powered up.

I have read of a few instances of this and it always seemed like the cause and the solution were usually different.

It would be great if we could get a complete list of all of the different causes that were found and what the individual solutions were.

I, too, would like to see this.   In saying that, I run Legacy and DCS on my layout, and have not encountered the issue being discussed in this thread.   I would like to be able to preempt possibly issues if ever helping setup a club or show layout.

Well, getting a "complete" list of all the causes is most likely the impossible dream!  By your own admission, there are varied causes, and I'm sure we haven't actually properly identified the root cause of many of the interference issues.  For instance, Joe posted a unique issue that I had never heard of before!  The TMCC being a separate layout and not connected to the tracks with DCS is a new one, I had never heard of that issue before!

A perfectly fine Legacy/TMCC zapping DCS when it’s turned on? Are we sure it isn’t a feature?

Just kidding!!! 😉

Just good engineering I would think!

I wonder if it's VSWR related.  Like once you get close to an even division of the wavelength of TMCC,  you have yourself an impedance matched load that is super effective at radiating the signal.

Remember, the wavelength of the TMCC signal is over 2000 feet.  I have difficulty believing this is the root of the problem.

Did you or Dale scope the TMCC or Legacy signal as a prelude to building the booster ?

'scoped it many times.  I'm sure I must have posted some 'scope pictures here at some point.  The TMCC command base (BASE1) has about a 3V P-P signal, the Legacy base has about a 5V P-P signal.  Unless you have a large or problematic layout, you could cut down the amplitude of the Legacy signal to about half and see how that works out.  I have no idea if it would make a difference in the DCS interference, but it might.

Could the DCS signal interference be caused by the ~2.4GHz wireless signal the Cab 2 and 990 base use to communicate.  Would it be worth trying different Channels on the Legacy system?

Legacy V1.6 manual p.78 lists the 9 different channel options from 2404.0MHz, 2412.2MHz, 2420.4MHz, ..... up to 2480.0MHz.

Really difficult for me to believe the low power 2.4ghz signal is affecting the much lower impedance 3.27mhz signal on the tracks.  I'm not saying it's impossible, just that it would be way down the list of things I'd be looking at.

Isn't the issue with the DCS wireless remote receiving low signal strength as soon as the Legacy system powers up?  That's why I'm wondering about the possibility of heterodyning among all the signals being transmitted, interfereing with a clear DCS wireless signal.  It seems like trying a different Legacy channel might be worth trying as it's easy to do and check to see if it makes a difference.

I've experienced similar issues in the wireless audio realm where multiple transceivers from different manufacturers cause interference with each other in close proximity.

The issues being discussed here have nothing to do with the communication between the remote and the command base or TIU.  We're talking about the DCS track signal getting stepped on by the TMCC track signal.

If you are having remote to TIU/BASE communication issues then changing the channel is a very good idea.

Just wondering if, based on the 3V P-P TMCC signal and the Legacy 5V P-P signal, it's possible to calculate what size resistor you would need to cut the signal, say in half, and how you would integrate the resistor into the system.

Would it be as simple as just splicing it into the "one wire" ?

You can start with a pair of 300 ohm resistors, one in series with the lead and the second one at the track connection to the earth ground connection.  It's a simple voltage divider.  I do something similar on my TMCC test set to attenuate the signal for testing if boards can detect a weak TMCC signal.

@gunrunnerjohn posted:

The issues being discussed here have nothing to do with the communication between the remote and the command base or TIU.  We're talking about the DCS track signal getting stepped on by the TMCC track signal.

Are we sure about that?  Could it be that the 900MHz signal to the TIU is being corrupted somehow and then passed onto the track in that corrupted state?  I thought I read that the logical signaling at the 900MHz carrier is the same as that on the rails, just that it's modulated differently.  If OTA signal corruption hasn't been ruled out, it should probably be run to ground (no pun intended).  However, if the TIU first validates the contents of the command and then rebroadcasts it then this is less likely to be the case.

I'll second @SteveH comparison to wireless microphones.  Once you have several transmitters at play, you have to look at the intermodulation distortion that can occur between two frequencies - far apart as they may be - and how that can affect other signals.  For instance, the IMD products from the 455kHz signal and the 3.27MHz signal could cause something else entirely to be radiated or the combination of 455+2.4GHz - or all three.  Heck - it could be related to the interplay of the those signals with other signals present at the location - TV channels, mobile phones, WiFi, etc.

The wireless microphone manufacturers have created software applications that take into account local broadcast stations, and all of the wireless mics in use in a given location and other TV band devices registered in that geographic location to calculate the best channels to put the wireless microphones on.  I'm not saying that is required here - but I think it's certainly worth a look as to whether or not the corruption happens at RF stage - or as @Adrian! indicated it truly is caused by the increased noise floor and the inability of the DCS decoder to pull the signal out correctly.

I don't know about "we", but I'm sure that the remote to base/TIU communication is not the root of the issue of TMCC affecting the DCS track signal.  You're free to explore that rat-hole if you like.   The relative signal strengths and impedance of the two different signals is vast.

You are also forgetting that the remote communications goes through a processor and is error checked before it's processed before it's turned into the track commands.  I don't know where you read that the remote to TIU communications is exactly the same format at the track signals, but I can't even imagine that being the case.

@gunrunnerjohn posted:

You can start with a pair of 300 ohm resistors, one in series with the lead and the second one at the track connection to the earth ground connection.  It's a simple voltage divider.  I do something similar on my TMCC test set to attenuate the signal for testing if boards can detect a weak TMCC signal.

Perhaps the OP will try this and report back.

@gunrunnerjohn posted:

The issues being discussed here have nothing to do with the communication between the remote and the command base or TIU.  We're talking about the DCS track signal getting stepped on by the TMCC track signal.

If you are having remote to TIU/BASE communication issues then changing the channel is a very good idea.

Please forgive my unfamiliarity with the DCS system.  John, between which devices is the DCS signal strength measured and then displayed on the remote?

In my situation I am using the WIU and the DCS app on my phone so even if signals between the remote and tiu could be an issue it wouldn't be in my case.

I have been busy and haven't been able to get to the layout at all this week.  When I have some time I will try to do some testing and report anything I find.

Just throwing this out as a question.  Is there anything a particular type of track system could be doing to amplify the legacy signal?  I am using gargraves phantom track and ross switches.

Michael