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Don't laugh out loud. I was the one who built the original signal booster. It used 2 vacuum tubes and a hand wound final output coil. Several large TMCC railroads with signal problems built it and it worked and solved their problem with TMCC signal loss. I am still using my vacuum tube one. Several people wanted a more modern one that was solid state. Dale took up the challenge and that is where it is today.

I used a 6X4 for the full wave rectifier. A small power transformer with 6.3 volts and 250-0-250 volt secondary. A hammond part. The tube used for the amplifier was a 6AQ5 beam power tube. The output coils was custom wound on a piece of PVC water pipe and tuned 455 Khz. The schematic was on this forum at one time. Might still be there somewhere. If it is not and you are really interested I still have the plans and diagrams.

I observed the signal from my vacuum tube model and calculated the output. The waveform was no higher in Peak to Peak value than a standard TMCC base. As a matter of fact I did experiment with boosting the signal higher than the normal TMCC output and found that had little if any effect. The real advantage to my circuit was the custom wound output coil that was tuned to 455 Khz.

If you take an oscilloscope and look at the electrical signal on a large layout you will find a massive amount of electrical noise. So bad as to the point of obliterating the TMCC base signal. It just makes if to hard for the receivers to filter out the signal they need. The output coil in effect shorts the outside rails to ground and gets rid of the noise. The primary of the coil is in the plate circuit of the 6AQ5 and actually steps down the output since the primary has more windings than the secondary. In short it does more to clean up the signal by shunting the electrical noise ( all those rails are a huge antenna for any RF in the area ) and then only apply a clean TMCC signal.

A simple observation of the TMCC output signal from the standard base with nothing connected and the output of signal of my device are virtually the same. The advantage of my unit is that it couples to the track much better than a TMCC base output and shunts all other signals and noise to ground, reducing their intensity so the actual TMCC signal can now be clearly seen on the oscilloscope.

I did promote it as a linear amplifier at one point but I found that a signal with more amplitude was not any real benefit. The real trick is to get the TMCC signal injected onto the rails with a device that has really low impedance. The standard TMCC base does not do that.

I got sideways with someone on the forum over it and the subject was blocked. Dale did a good job of converting it to solid state and I have never seen his diagram or what was done to help with impedance matching of the output.

There was nothing illegal about the power output level of my device.

Last edited by Jim LeFevre
@Jim LeFevre posted:

Don't laugh out loud. I was the one who built the original signal booster. It used 2 vacuum tubes and a hand wound final output coil. Several large TMCC railroads with signal problems built it and it worked and solved their problem with TMCC signal loss. I am still using my vacuum tube one. Several people wanted a more modern one that was solid state. Dale took up the challenge and that is where it is today.

Bob at NJ-HR said they cooked their tube one tinkering with the final output coil turns ratio, they currently have at least two of the solid state model, obviously only one in active use.

Some interesting background on the buffer, this is something Dale wrote in 2013 before he designed the solid state model.  I also found the tube schematic

Vacuum Tube Booster Amp for the TMCC Track Signal.pdf

TMCC Amp Schematic with ref numbers.pdf


When I suggested using a vacuum tube based model it if course was in jest, but not surprised someone would actually doing that, I am impressed

As far as the output power of a tube model being too high that is a matter of how well it is designed, tubes are high energy devices (the voltage taken to excite them), but the power output is a function of the design and how many tubes are used and what type.  If this was a commercial unit it is true that it would need to be certified under part 15 of FCC rules, but a home brew unit doesn't have to meet that. The person using this might screw up reception in their own house, but unless it was affecting people in other houses (unlikely) there is no law involved.

Send me an email so I can put you in the request queue.  I am ordering parts for ten of them, most are already spoken for.

Hey John,

Give me a call about this.  I think OGR might be interested in this for our / my layout.  Perhaps a couple...but I would rather talk via phone without others having to put up with my questions in this thread!  Thanks!

Let me say that I bought the components from GRJ a while back and added the buffer to our layout. Totally improved the reliability of the Legacy locos. No issues since adding it. It's worth the small amount of money and little time of construction. Wish there was something like this for DCS....... Thanks again to all who worked on this project!

@cjack posted:

Interesting thought. What’s the nature of the DCS signal?

The DCS signal is bi-directional, and the ability for the locomotive to talk back can't be amplified without internal control from the DCS controller, AKA the TIU.  The DCS signal is also just present when there is a command coming and going, and it's mandatory to know what is happening in the command so you know when to turn the buffer off.

@Adrian! did quite a bit of research on this topic, and no practical solutions were forthcoming.  If he can't get it working, I'm not going to even try!

TMCC/Legacy, OTOH, is a unidirectional signal that can be easily buffered because it's always there and it only goes out, there is no return traffic.

The TMCC buffer is simple in concept, any buffering of the DCS signal is anything but simple!

@cjack posted:

Interesting thought. What’s the nature of the DCS signal?

Per John above .... Reposted for you:

Legacy is one way (base to train) signaling, so "buffering" is easy. The triangle (amplifier) points away from the base and towards the train.

The first issue is DCS is two way (train to TIU and TIU to train) signaling... so buffering is complicated since ... which way would the triangle point? If it just points one way it's not helpful since it will isolate in the other direction and you'll have no reverse signaling... and if you put two pointing both ways.... well then its just a loop of two triangles and now you have an oscillator. To do this successfully, you would need to "know" when a packet is about to go in one direction or another and switch in or out your triangle directions accordingly, which means the switching thing you build needs other logic signals from deep within the TIU (tapping the logic upstream of the output drivers)... to give your switch enough time to get the amplifier setup. Not easy with a big layout that has 20 or even more different TIU channels. You would need to tap all that logic on all the TIU channels in the layout to see when one of them somewhere is about to transmit a sequence.

The second part is the DCS packet timing:  While we do know the sequence is always TIU-to-train before Train-to-TIU the TIU-to-train part is variable length (different commands --> different times) so it's not as simple as having an RC timer or something switch the triangle direction after a certain time constant so the amplifier points one way then the other. Unlike the TIU (who's firmware knows what command it is sending and what packet length it will be, and what response length to expect), you the outsider would need to extract this information from the outgoing packet to get these details for setting direction, and you would need to do it very very quickly since the packet you're decoding is also the packet you're steering the triangles for. That also means you're going to need some kind of fast look-up of the outgoing commands, too much for a microcontroller, it'd have to be an FPGA with a respectable clock... so now you're getting into the $1000 range.

The third issue is that we're talking about trains which move: Like mentioned above it's TIU-to-train, and train-to-TIU signaling. Understanding where to place the TIU-to-train amplifier is simple... you'd put it at the TIU before the connection to the layout... but how would you place the amplifier for the train-to-TIU  signal? If you place it at the TIU, well the signals already gone through the layout at that point and all the ringing, distortion, and noise is already in there so an amplifier won't help much at that point. You'd need to place it inside the train (at the point where the transmission originates and is "clean")... That is you'd need to put modules in each locomotive one by one... with a $1000ish FPGA inside tapped into the PS2/3 board to get timing info.

The more you think about it ... the less sense it makes... and that's why we don't have such a booster.

Cell phones are full duplex, so they don't have the issues of determining where a data packet starts and ends.  DCS is a single channel that can only handle traffic in one direction at a time, so there has to be a traffic cop to determine when it's OK to talk.  As Adrain! says, the other major issue is a single DCS channel only services at most a couple hundred feet of track, so any logic has to be duplicated over and over.  Finally, the engine return traffic being amplified is very costly.

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