[Gordon H]

QUOTE (Expat @ 14 Feb 2008, 12:11) <{POST_SNAPBACK}>If you have a DCC ring main and you send a signal/instruction to a loco which is on a section of track which is connected say 1/3rd of the way round the DCC ring main the signal will actually travel in both directions around the ring main and will arrive firstly along the shortest route between the controller and the loco.

However, milliseconds later, the signal will arrive again along the longer route between controller and loco.
Not milliseconds. Nanoseconds at the most - one million times less.
To get a difference of one half of a DCC '1' bit (58 microseconds), the path difference would need to be about 17.4km!!

QUOTE The loco will therefore receive the same signal twice which can, apparently, cause its little brain to become confused and may result in unpredictable consequences. Hence you should use a DCC Radial Bus to ensure that the signal/instruction only arrives once at the loco.
Once more...
The frequencies involved in DCC are way too low, and layouts sizes are way too small, to cause problems of this kind.
Try it both ways - see if you can detect a difference.

 

[Gordon H]

QUOTE (Richard Johnson @ 14 Feb 2008, 14:01) <{POST_SNAPBACK}>Technically why - it des NOT matter - it did the job... removing the ring worked. Adding the 150 ohm resistor+ 10microfarad apacitors as resistors worked too. Which was most responsible for the improvement, I have NO idea - I don't take a digital storage scope with me to look before I act.
But it does matter.
Apparently solving a problem without knowing how or why the cure works does not really constitute a solution, certainly not a repeatable one. Without understanding its mechanism, you cannot know for sure that the problem won't re-occur when presented with a slightly different, but equally valid set of conditions.
A DSO is precisely the sort of thing that SHOULD be taken along when investigating this kind of matter, so that the effects can be understood and quantified for future reference and explanation. Otherwise, we go round the whole thing time and again when others inevitably ask the same question.

 

[Gordon H]

QUOTE (dbclass50 @ 18 Feb 2008, 12:06) <{POST_SNAPBACK}>Exactly - you don't have to know why a car (or computer, or telephone or..........) works to use it & use it effectively & reliably !
But you will need to know something of how a car works if you going to be wiring it up yourself.
That is effectively what buyers of proprietary DCC equipment are doing, quoting this example.

Admittedly, as an engineer, I will always want to know the 'whys' and 'hows' of such matters rather than just being presented with an apparent fix with nothing to back it up.

What most people seem intent on overlooking is that creation and running of railways, both real and model, is an engineering task whether they like to admit it or not. Electrical, mechanical and civil engineering are all involved to some extent, and until you can go to a shop and buy a completely finished RTR layout with rolling stock there will always be a need to have some understanding of the principles involved.

OK, transmission line effects on DCC waveforms are a bit esoteric for a list such as this, but the question did arise, and solutions were offered - which in principle ought not to be necessary based on the engineering figures available. In that circumstance, where the theory doesn't necessarily agree with practical experience - surely it is acceptable to ask for an explanation?

 

[Gordon H]

QUOTE (poliss @ 19 Feb 2008, 01:28) <{POST_SNAPBACK}>The language needs to be simplified. To most people, a bus is something you catch, radials are the tyres on the bus. Choc boxes are what you give your girlfriend on Valentines day. Daisy chains are things girls make at school.
The problem here is that the language has already been simplified, or at least adapted from elsewhere, to be rather more descriptive than precise.
This, of course, is part of the overall problem - so few people are familiar with technical matters, and the terminology involved, that these more descriptive versions become prevalent, often leading to their use in several different, and usually unrelated contexts. Spare a thought for those of us using a PCB design program which uses the term LMS for 'Library Management System'. No matter how hard I try, the obvious railway context simply refuses not to come to mind first!

From my point of view, I will admit that I find it hard not to want to know how things work, especially when they are related to my usual spheres of activity (i.e. electronics). I cannot imagine being in a position where blind acceptance of things magically working around me without at least a rudimentary understanding of the principles involved is acceptable.

 

[Gordon H]

QUOTE (iansa @ 19 Feb 2008, 23:31) <{POST_SNAPBACK}>The old saying says " I don't know how the watch works but I can tell the time".

30yrs in model railways, the last 13 in DCC and the old saying has served me well.
Then I guess you see yourself as the Managing Director of your railway, rather than the Chief Engineer?