Two whistles from a single DCS command

Guessing a DCS signal echo?

Gray,

This has been fondly referred to by a friend as a “double toot” and has been around for quite some time.

It seems to occur with only a small number of DCS engines and is reputed to be due to some kind of DCS wiring anomaly, perhaps an undiscovered connection between the center rails of 2 adjacent track blocks.

Regardless, if it occurs only infrequently you may be content to just live with it. It’s not a very serious issue.

I am he to whom Barry refers.  I originally got the doubletoot only in one block, and about 5 years ago it spread to entire layout, which has 70 blocks over 6 TIU channels.  Tests have failed to disclose any interconnections.  But, when there are lighted cars or locos on the layouts, center rails do have electrical connections via the outside rails.  Placing one lead of an ohmmeter on a center rail in one block, meter current flows from the lead through the track to a pickup roller to a bulb to an outside rail and from an outside rail, through a wheel, bulb and roller to another center rail.  Does that do it?---Who can tell.

Some engines, both PS2 & PS3, seem more prone to doubletoot than others.

MTH in-house gurus say there could be induction between leads.  Seems to go away if I turn off one TIU.

Don't waste your money on getting a newer TIU; doesn't make a difference.

Gentlemen,

  Every once in a while I will also get a double announcement like the double toot.  My TIU's are very close to each other, mounted on the wall, and I believe this may be the problem.  To me however it's no big deal and I just leave it alone.  RJR is correct if I turn off one of the TIU's it eliminates all the doubling.

PCRR/Dave

Picture taken work in progress, just prior to permanently connecting most of the track runs.   I probably should have separated the TIU's further away from each other.

I only have one TIU (rev H) and get the double toot 99% of the time.  Currently I have two channels running 11 blocks each with each an aggregate of approx  240 feet of track.  Will be changing to 4 blocks relatively soon with 5-6 blocks each and 120 feet of track.  Will see if that changes things.  Currently I'm just ignoring.  

My bigger need (I think) is to make the external antenna mod to the TIU as I sometimes have trouble at about 55 ft of distance between the remote and TIH.  Sure would be nice if MTH put an external antenna jack on the next TIU rev.

Dave,

My TIU's are very close to each other, mounted on the wall, and I believe this may be the problem.

Nope, that's not it.  

When I get only a certain engine that will double toot for me, I perform a signal test with it and compare it to other engines parked at the same location. Most times I find a slightly weaker signal with the double tooter. One must realize a loop is created with the track, 2 pickup rollers, and the wiring that is joining together the rollers with the wire nut in the engine. So the signal is coming from two locations to the wire nut where it must be absorbed by a single wire going from the wire nut to the circuit board. I like to remove the wire nut, scrape the wire clean with a razor, then re-twist the ends and solder them together. This gives me maximum continuity where the signal collision occurs and gets absorbed by the circuit board wire. Then I take a tooth pick and push the terminal connector end of the circuit board wire further down into the plug, so that it is seated deeper onto the circuit board pin. I then like to do that with all the wires in all the plugs on the circuit board. Lastly I clean all the ground wire connections and make sure the ground wire screws have no paint under the heads and are good and tight. I have eliminated many double tooters doing this and increase their signal reading. You may also want to try 18 volt bulbs connected directly at the outputs of your TIU. That has also helped when its a problem with all engines. Even though I use the lighted lock-ons, it didn't help until I put bulbs right at the outputs.

Good advice from above post..especially removing the black coating on the truck pickup screws.My latest ps3 diesels do not have the black  screws from the factory.