18V or 24V Bulbs?

Stick with 18-volts, #1445 or #1447.  On DCS forum, some have reported 24-volt bulbs to be less effective.

These bulbs will run hot so be aware the bumper lenses may soften or deform.

24 v bulbs run pretty yellow at 18 v, and they draw more current than one would think for 25% less voltage...more like only 10% less. So you don't save much heat or power.

What exactly is the issue with DCS in this regard. Is this a transmission line reflection issue and the "filters" or bulb loads help to terminate the "transmission line" or track?

It is to help with the reflection of the signal on a siding. That is how it was explained to me.

Yep, the higher frequencies of DCS, as well as the fact they run on the outside and center rail, cause a transmission line effect.  The bulbs apparently reduce reflections of the signal.

Thanks. I was just wondering what the characteristic impedance of O gauge track would be. Of course there are all sorts of issues with calculating this...and probably doesn't matter that much. It's probably just that one has some kind of load...like a bulb.

What is the "filter" that doesn't cause heat like a bulb?

On our layout the 24v blubs degraded the strength of the DCS control signal.  It went down from 9-10 to 4-5 in most instances.  But it wasn't as bad as the now discontinued OGR "Magic Bulbs" which dropped the signal to 0-1 ...

I use the ones I have left as a "current on" indicator powered by a transformer which does not connect to anything else.  That works okay ...

I believe Susan Deets son did some measuring, calculating and came up with an optimal set of capacitors, resistors and maybe an inductor values that "tamed the wild beast".  Sure she will chime in.

I also believe it was Marty Fitzhenery (sp?) who discovered this trick when he was beta testing the prototype TIU before it was sprung on the public

Don't have a clue what the characteristic impedance of the track would be, and I'm guessing it would vary wildly with different layouts and different rolling stock mixes.  The unterminated ends of sidings seem to cause the most issues, which is why they were were the bulbs or filters were being placed.

Please don't call it a filter.  It is an AC-coupled termination.

Now I get it...interesting how the properly descriptive term better describes.

It got the moniker of Filter because that's the name the person building and testing them hung on them. But they are a Transmission line Termination in operation.

Note that many of them are not installed at the end of the track block, but at the power drop to the block (Modular layouts). They then serve to reduce reflections back onto the distribution net of the Power/DCS signal.

I really don't care what it's called, Just like the fact it works, and uses VERY little power to boot.

Correct, it's a termination, but everyone's been calling it a filter, so...