Striking signal difference for PS3 vs. PS2 locomotives--common experience?

GRJ: Thank you. Digikey has long lead time for pot now, found supplier via Amazon who says delivery by Mar 10 (hope true).  Ordered two in case I manage to hurt one.  Will report results.  I guess if it remains unresolved that oscilloscope may be in my future    He who dies with the most tools and test instruments wins? Dubious.

Understand why you’d not want to offer “fix” install now that you explained.  Will watch with others for report of your simpler fix and results.  So far it doesn’t look like my problems involve dying TIU channels (knock on wood), so it’s not an urgent issue here.

Yep, Adrian's fix looks pretty labor intensive, don't think I want to get into that. 

As for the Digikey part, I don't understand the lead time issue.

gunrunnerjohn posted:

Yep, Adrian's fix looks pretty labor intensive, don't think I want to get into that. 

As for the Digikey part, I don't understand the lead time issue.

Maybe I misinterpreted: saw "mfr lead time" of 14 weeks somewhere in Digikey listing.  Thanks, may order another then to insure quickest delivery.

Forgive, but back to my question about a choke on the output of the Legacy or TMCC base.  I meant, one that would filter above say 1 MHz or some suitable choice above TMCC frequency range, to decrease DCS-range stray frequencies headed for track.  Messing about with research this morning, example choke found, so specifically would one like this not work well for a reason not clear to me? If I read right its peak impedance is at 4.1 MHz, in the lower part of the DCS range.  Does it cause a problem with TMCC signal strength, or as simply as possible why would it not be effective, if not?

https://www.coilcraft.com/cq7584.cfm

Got out one of the "important" locos yesterday, PS2.0 C&NW E4 streamlined Hudson, loco for the Challenger in the late 30s as well as mail/express trains into the early 50s.  With TMCC not present, perfect function and "10" signal everywhere.  Now to keep that and get TMCC back   That would be Christmas here!

Hope we can learn something. Thx again.

Adrian did quite a dissertation on why you can't keep the TMCC from potentially interfering with DCS, complete with pictures somewhere on the forum.  Suffice to say, if it were as simple as dropping in a choke, we'd have already done it.  If only it were as simple as dropping in a small filter.

Thanks.  I'll try to find the dissertation on my own-enough!

Don

Latest test results: with both blocks connected to each channel, 130 ft of mainline per channel again, signal 10 everywhere with PS2.0 steam loco.  TMCC signal remains NOT connected to layout.  After adding about 30 feet of 10 gauge wire for voltage drop reduction, in parallel with existing 14 ga lines from TIU output to track bus on one block, still signal 10 everywhere.  No sign that capacitance from the added heavy wire did harm in this instance.  Similar 10 ga addition planned for other block, will report.

Waiting for alternate potentiometer suggested by GRJ to go in DM TMCC buffer, to further reduce signal voltage/amplitude of buffer output.  Will see if that allows TMCC to be connected without wrecking DCS signal.

Just found this 2/5/16 post on “TMCC Engines killing DCS signal” thread, by Marty Fitzhenry.  Is this pertinent to the current discussion?  The thread may be titled for engine interference, but Marty’s post seems directed at signal interference from the Lionel base.  I don’t remember the exact age of my Legacy base, but it’s pretty old.

”Gary, I have the ESE engine with no issue.  When Legacy first came out it was built on a similar TMCC platform of modular boards.  Motherboard with an R4LC, Railsounds power board, and Railsounds audio board.  Both TMCC and early Legacy shared the same Railsounds power board. Issues were noted with DCS signal.  That lasted for a short time.  If you pulled the Railsounds power board with the engine powered on the track the signal issue in most cases was not an issue.

You can try just the engine as the tender no longer uses the old Railsounds power board.  The newer Railsounds Lite board has never been an issue here.  Also please set your ESE engine on the track powered with a DCS engine on the same track under a signal test..  Try turning off the smoke in your ESE and let us know what you see.  I have seen smoke fan motors on the edge do strange things.  If you are using Gargraves track without theground rails tied together do the same test I mentioned above and using a jumper, connect both outside rails. 

I get to see a few more Lionel engines than most and I am a huge fan of the RCMC board system.”

Here are a few of the threads where this was discussed.

Correlator Noise floor inflation by Legacy Signal Interfering with DCS

Circuit Filtering to Separate Legacy/TMCC and DCS signals

DCS/Legacy Interference

I found Adrian’s “dissertation”, his thread: 

https://ogrforum.com/...tmcc-and-dcs-signals

Unless I misunderstand, this is directed at filtering between all signals and the track, and not in the line just from the Legacy or TMCC base to the track as I was asking (I’m not suggesting interposing the filter or choke between the TIU output and track, as Adrian’s post implies.)  His explanation addresses the filter causing blockage of some lower frequency aspects of the DCS signal, if the filter sits between the DCS signal source and track, if I understand correctly what is implied.

I don’t think it answers the question whether one of those filters, or a simple choke of the right inductance value, might reduce TMCC’s interference with the DCS signal if it was placed between TMCC/Legacy base and the rest of the system, upstream of the entry of the DCS signal.

gunrunnerjohn posted:

Here are a few of the threads where this was discussed.

Correlator Noise floor inflation by Legacy Signal Interfering with DCS

Circuit Filtering to Separate Legacy/TMCC and DCS signals

DCS/Legacy Interference

 

Thanks, reviewed.  I notice a couple of things
1. At one point you suggested including one of Adrian’s solutions in your DM TMCC buffer, but I didn’t see the follow-on to that line of thought.  Abandoned for some reason?

2. I think it was Adrian who noted that reducing buffer output voltage as we’re about to try here, has the problem of reducing the S/N ratio for the TMCC signal.  (Not sure I understand, would think ratio unchanged, but absolute difference between signal and noise amplitudes WOULD be reduced, which may still cause a problem.) Yes, might be a drawback?  (Still worth trying, can’t know net result without a trial).

If you reduce the amplitude of the TMCC signal, by definition you'll reduce the S/N ratio, think about it.   However, the TMCC will work at a pretty low level as a rule, and by reducing the amplitude of the TMCC signal, you also reduce the likelihood of it interfering with the DCS signal.

I have my doubts that a simple choke between the TMCC command base and the track is going to fix this, but obviously it's cheap to try.  In order to do such testing, you have to have a location that actually has the issue of interference, since I don't have that, I haven't pursued such fixes.

Noise is coming from other sources than the TMCC and buffer outputs, I get it, so ratio does decrease.

If you'd share your educated guess for a simple inductor choke value (and a part number?), I'll get one and try it.  This was my uneducated guess a couple of days ago: peak impedance is at 4.1 MHz, in the lower part of the DCS range.  Realize from Adrian's "dissertation" that some aspects of DCS signals have frequencies in the TMCC range, so if those are what is being interfered with, a choke won't help that part.  Maybe that line of thought would lead to a choke value in a lower frequency range, closer to the TMCC's top end, though?

https://www.coilcraft.com/cq7584.cfm

Thanks!

GRJ: BEFORE launching on this, did you have a comment re: Marty Fitzhenry's 2/5/16 post on “TMCC Engines killing DCS signal” thread, about newer Legacy bases not having DCS interference issues (noted above?)  Forgot to prompt that question again.

How do you figure 4.1mhz is the lower part of the DCS range?  The basic carrier for DCS is 3.27 mhz, but as Adrian states, it can get down to less than one mhz for some signal bursts. 

TMCC really doesn't have a "top end", it's an FSK signal that is closely centered around 455khz.  The modulation bit rate for TMCC/Legacy is around 3,000 BPS.  You won't find it spread out like the DCS signal.

I truthfully don't have an "educated guess" on a choke that will do what you're seeking, which is why I've not responded with a suggested part.  My education is telling me that it's not possible to filter out the interference while still keeping the TMCC signal.  Since the TMCC signal doesn't have a wide spectrum, I feel that amplitude control is the best route to balance the TMCC and DCS operation.

cnwdon posted:

GRJ: BEFORE launching on this, did you have a comment re: Marty Fitzhenry's 2/5/16 post on “TMCC Engines killing DCS signal” thread, about newer Legacy bases not having DCS interference issues (noted above?)  Forgot to prompt that question again.

If you provide a link to the post, I can comment on it.  As far as TMCC/Legacy engines sometimes causing DCC issues, this is a well-known issue, and there's a well-known cure.

Sure.  It was Marty's 2/5/16 post on this thread: https://ogrforum.com/...s-killing-dcs-signal

Thanks

Found resolution to confusion here:  "We started seeing the RCMC board in 2010. The Vision Line Hudson was the first VL locomotive to have it."  In this thread: 

https://ogrforum.com/...board-to-rcmc-boards

So the board change was in the engines, not the base as I wrongly inferred from reading Marty's thread.

I've actually been asked to write something intelligent here (a first)... so let me try...

Uh so like, PS2, PS3 whatever, you need to first make sure the layout isn't sad. Specifically (1) the amplitude of the DCS waveform is you know, not awful (>10V excursion)...  and (2) the waveform shape is sharp and not a sawtooth like thing, ringing like a mess. If the DCS waveform or amplitude is a mess you should fix that first, definitely. Many posts are dedicated to how to do that, and many people here can help you (esp GRJ).

Now beyond "the layout having issues" I have seen that the DCS amplitude measured at the track is vastly different with different locomotives on the track. For example I've seen where a PS2 SD-whatever train knocks the 14V amplitude down to about 4V swing, while my giant DDA40x PS3 trains only drag the same signal down to 10-11V, which implies the impedance loading of different trains is different. The PS boards have something sort of like a Diplexer that separates the 60Hz and 3-12 MHz DCS signals. The 60Hz is sent to the rectifier block, while the DCS is sent to the CDMA decoder. The diplexer basically works by being a frequency selective series impedance to keep the 60Hz out of the digital decoder part, and keeping the 3-12 MHz out of the power rectifier circuitry (and down stream lights and motors).

I suspect what is going on is the diplexer design has been revisited from PS2 to PS3 to greatly reduce how much of the DCS signal power flows into the rectifier system. This also suggests that if you lift off one of the AC input pins of the rectifier bridge on the PS board and slip a choke in series with it, you can improve the diplexer performance further since the choke will raise the impedance at 3-12 MHz, while basically still being a 0 ohm element at 60 Hz.

Marty was talking about the cable between the Legacy command base and the TIU, apparently there was some issue there that was solved with an opto-isolator.  That has nothing to do with the TMCC signal on the track affecting the DCS signal, that's the problem we're talking about.

Interesting idea about adding a choke to the PS/2 board, never thought of that.

Adrian! posted:

I've actually been asked to write something intelligent here (a first)... so let me try...

Uh so like, PS2, PS3 whatever, you need to first make sure the layout isn't sad. Specifically (1) the amplitude of the DCS waveform is you know, not awful (>10V excursion)...  and (2) the waveform shape is sharp and not a sawtooth like thing, ringing like a mess. If the DCS waveform or amplitude is a mess you should fix that first, definitely. Many posts are dedicated to how to do that, and many people here can help you (esp GRJ).

Now beyond "the layout having issues" I have seen that the DCS amplitude measured at the track is vastly different with different locomotives on the track. For example I've seen where a PS2 SD-whatever train knocks the 14V amplitude down to about 4V swing, while my giant DDA40x PS3 trains only drag the same signal down to 10-11V, which implies the impedance loading of different trains is different. The PS boards have something sort of like a Diplexer that separates the 60Hz and 3-12 MHz DCS signals. The 60Hz is sent to the rectifier block, while the DCS is sent to the CDMA decoder. The diplexer basically works by being a frequency selective series impedance to keep the 60Hz out of the digital decoder part, and keeping the 3-12 MHz out of the power rectifier circuitry (and down stream lights and motors).

I suspect what is going on is the diplexer design has been revisited from PS2 to PS3 to greatly reduce how much of the DCS signal power flows into the rectifier system. This also suggests that if you lift off one of the AC input pins of the rectifier bridge on the PS board and slip a choke in series with it, you can improve the diplexer performance further since the choke will raise the impedance at 3-12 MHz, while basically still being a 0 ohm element at 60 Hz.

 

 

 

Thanks for responding to my email.  Uh, like, that was pretty intelligent.  

Thanks to GRJ's advice, will shortly try different potentiometer in his TMCC buffer to reduce TMCC v/amplitude more and see if the TMCC signal improvements keep it effective at lower amplitude, while reducing DCS interference problems.  Watch this space for a report.

If I later need to address problems with some individual DCS locomotives: For cutting off above-60-cycle input to the rectifier bridge, sounds a simpler assignment than the impossible one of cutting between overlapping TMCC and DCS frequency ranges, as pointed out by GRJ.  What KHz or MHz value recommended for peak impedance, if that is pertinent spec? (or which spec to pay attention to?)  I get that the choke has to have a 4-6 amp current rating because it will pass the motor and other loads.

I suspect a whole lot of folks gave up on this battle long ago, if they had the same challenges.  It would be good to find solutions.

There is plenty more practical detail to testing this, but it’s encouraging enough to require a report!

The alternative potentiometer arrived today and I installed it in your DM Buffer, GRJ.  To put it decorously, that was a pretty good SWAG!

First, with the gain turned all the way down, a TMCC locomotive still hears its signal and performs normally in limited initial testing, so your hypothesis that signal quality would permit dialing down signal voltage and still give good TMCC function seems correct so far.  Haven’t tested that everywhere on layout, but there seems to be room to adjust upward as noted next:

The PS2 steamer is the DCS test subject again.  With TMCC gain at minimum and also with it at half-scale (meaning half of knob excursion, not measured resistance) on the new pot, I still get signal 10 and normal function including at a layout spot where there was a “4” and malfunction before with TMCC on the layout.  But when the gain on new booster pot is turned all the way up, we’re back to “no signal” or “loco not found”, so the baseline situation hasn’t magically changed.

Since there seems to be at least half of the gain scale available to tune upward for TMCC function if that is weak somewhere on layout, or downward for better DCS function if that is weak in places, there’s room for optimism that this will work out.  Lots more to follow in terms of detail of testing both DCS and TMCC/Legacy function in different layout locations, but it’s a great day so far .  Thanks for your patience with all the naive questions.  Maybe this will help someone else, too.  To bring the info down here for someone ready to order a pot, your recommended part is Bourns, mfr part # PDB181-K420K-502B.

Sounds like you're on the road to happiness.  I think I'll lay in some higher value pots for issues like this if this works out for you.  FWIW, the main part of that SWAG was Adrian's work on the TMCC/DCS interplay, I just figured after his analysis that less TMCC amplitude had to be better for the DCS signal.