magic light

You can use 18v light bulbs or make filters with a resistor and capacitor.   The filters have advantages (minimal current draw, no heat, don't burn out) and the components are dirt cheap.   They were very effective on our modular layout.   Here is everything you need to know incuding where and how to wire them:

http://www.slsprr.net/technical/filter.htm

Bob

Dan,

From The  DCS O Gauge Companion 2nd Edition, page 61:

The Magic Light Bulb

Marty Fitzhenry was the first to note that placing an 18 volt light bulb across either the input to a terminal block or the output of a TIU channel can provide a great improvement in DCS signal strength. Why this works is much less important than the fact that it simply does. The author has seen improvements where DCS signal strength went from 4's and 5's to solid 10's simply by using the 18 volt light bulb across the input to a terminal block.

Additional light bulbs placed at the ends of sidings nearly guarantee that the siding will have a signal strength of 10. The author's practice is to place lighted bumpers on all sidings.

An alternative to using a light bulb is to use what is referred to as an "engineered filter". The engineered filter's inventor notes that "The filter consists of a resistor and capacitor of a specific values wired in series. The filters work best in pairs, one across TIU outputs and the other at the 'farthest' point from the TIU output."

A number of DCS operators have reported success in using these filters as light bulb replacements, particularly on buss wired layouts. For additional information, go to the inventor's web site at www.slsprr.net/technical/filter.htm

As regards use of light bulbs or engineered filters to improve DCS signal strength: 

• These devices should only be used if the DCS signal strength is lower than the operator desires 

• There is no guarantee that these devices will improve instances of low DCS signal strength although they tend to improve DCS signal strength when used with revisions of the TIU earlier than the Rev. L 

• To use these devices with the Rev. L TIU, first remove them all, install the Rev. L TIU, and then selectively add them back if and only if the DCS signal strength needs to be improved 

• While there are reports (by the author and others) that these devices adversely affect Rev. L TIU DCS signal strength, experiences of different operators, with different layout track topologies, may vary.

This and a whole lot more is all in "The DCS O Gauge Companion 2nd Edition", now available for purchase as an eBook or a printed book from MTH's web store site! Click on the link below to go to MTH's web page for the book!

Marty Fitzhenry was the first to note that placing an 18 volt light bulb across either the input to a terminal block or the output of a TIU channel can provide a great improvement in DCS signal strength. Why this works is much less important than the fact that it simply does. The author has seen improvements where DCS signal strength went from 4's and 5's to solid 10's simply by using the 18 volt light bulb across the input to a terminal block.

Still a mystery after all these years but it works really well.

I'm not sure it's a total mystery.  The incandescent bulb offers a termination to the RF transmission line and minimizes reflections that would corrupt the signal.  It's the same as when you have a 50 ohm co-ax and put a 50 ohm terminator on the end of the run.

Gunrunner your killing the mystery! A magician never revels his secrets. LOL. Here I thought the darn thing was actually magic.

I don't use them; I am one of the fortunate fellows who lucked out and have almost all 10's on my DCS signal. 

They are magic, I was just kidding.

Gunrunner:  Nice theory & makes sense, but they also sometimes do magic when not at the far end of a track or block, like at the TIU, where the "reflection" would come back to the initial source.

Yep, the normal recommendation is at the TIU and the far end.

John,

Yep, the normal recommendation is at the TIU and the far end.

That's only for the filters. The bulb should be placed either across the TIU channel output or at the entry to the terminal block.

Filters are a bit better suited for buss-wired layouts where the "farthest point" is more easily determined.

Barry, I placed 18-volt bulbs at the end of some dead-end sidings, which improved signals on the "main line" composed of separate blocks on same TIU output.

Barry, it's odd, I would have assumed that the bulbs should go on the far end, not on the TIU end.  I haven't used the bulbs, I've installed the filters as you describe and it has helped with our bus wired modular layout.  Still working in improving the signal...

Robert,

I placed 18-volt bulbs at the end of some dead-end sidings, which improved signals on the "main line" composed of separate blocks on same TIU output.

I'm not at all surprised.

When I added DCS to my previous layout, I was pleasently surprised to find that my signal strength was in the 7-9 range, in spite of the true "rat's nest" ofd 18 gauge solid wire that I'd created. It turned out that the decent signal strength was due to two factors.

The first was that I had implemented true track blocks with insulated center rails. The  second was that I had Lionel #260 lighted bumpers on all of my sidings, ay least one of which was always powered on.