DCC bus termination/filter . do they work ?

[posneg6]

I saw this simple and interesting article on Railway Scenics web page  "DCC bus termination/filter".
On long DCC bus runs, it could be worth adding a terminator kit to all open ends of your DCC wiring. The termination filter is a relatively simple cheap device that will filter out noise and voltage spikes created by a motors brushes, intermittent wheel to rail contact and intermittent short circuits, and will improve the quality of the DCC waveform  by minimizing reflections caused by the open end of the bus. Adding these low cost devices may extend decoder life and improve overall layout reliability. The termination kits we sell, include two components, a resistor and a capacitor. Neither of these items are polarity sensitive. A Capacitor across the two wires will cause a dead short to AC signals, such as the digital waveform used for DCC. The resistor is in the circuit to prevent it from being a dead short between the two bus lines.

Has anyone tried it?

 I'm going to get the parts today will let you know if it works. 

[WIMorrison]

I have them on my track and accessory bus - do they work? TBH I don't know but I do know that I haven't had the random problems of address reassignment on Cobalt IP motors that other keep having - and I use RailCom which is also said to cause issues.

 

My view is that whilst they might to do any good, they certainly dont do any harm

[JST]

Like WIMorrison I have fitted them but don't really know if they work. What I do know, is that since fitting them I don't get problems with some locos "running away" that I did before. I have surmised that the signal has been somehow stabilised.

[Crosland]

If you have a noisy bus they will help. No harm in fitting them anyway.

 

Don't get too hung up about where you fit them. They are purely filters for high frequency noise. DCC is not a transmission line, it's not about reflections, and they do not need to be at the end of every bus run.

 

 

[Damo666]

If your throttle connects at the middle of the BUS (middle of the layout), and your BUS then heads off left and right on an 'end-to-end' layout, would you need the filters at both ends or just one filter somewhere along the BUS?

[Nigelcliffe]

37 minutes ago, Damo666 said:

If your throttle connects at the middle of the BUS (middle of the layout), and your BUS then heads off left and right on an 'end-to-end' layout, would you need the filters at both ends or just one filter somewhere along the BUS?

 

Wrong bus (you stand here all day and three buses come along at once).   

 

Throttles connect to a throttle bus system.   These questions are about the DCC track feeds, also callled the DCC bus.  

 

[posneg6]

5 hours ago, Crosland said:

If you have a noisy bus they will help. No harm in fitting them anyway.

 

Don't get too hung up about where you fit them. They are purely filters for high frequency noise. DCC is not a transmission line, it's not about reflections, and they do not need to be at the end of every bus run.

 

 

Thats would be correct, you could put one in the middle of your bus , electrically its the same, it's across the the track anywhere. 

 

[Sir TophamHatt]

If you have problems, get one.

No problems?  Don't get one.

[Ron Ron Ron]

16 hours ago, Nigelcliffe said:

Wrong bus (you stand here all day and three buses come along at once)..................   

 

 

 

16 hours ago, Nigelcliffe said:

....Throttles connect to a throttle bus system.   These questions are about the DCC track feeds, also callled the DCC bus.  

 

As Nigel points out, there can be several types of DCC bus.

When people loosely refer to the "DCC Bus", they usually are referring to the Power Bus, which can be a Track Bus, Accessory Bus or both.

So why not say so?

 

These are quite different from other types of DCC bus, such as...

system throttle/cab bus,

combined system/cab buses (e.g. LocoNet, ECoSLink),

feedback bus,

Booster or control bus (original Lenz and NMRA terminology)

 

....and back to the topic, DCC Bus terminators/filters, are only applicable to the Power Bus.

 

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