I have been offered an Oscilloscope that a national cell phone company is retiring. I read somewhere you can use these to tune up your DCC system. Not being a electronics guru I am wondering if I should take it and learn to use it? Or is it something that is way over my head without being a electronics technician. I don't want it becoming a piece of equipment taking up space. I hate clutter. It is about the size of a small suitcase with many buttons and dials. Thanks for your input.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
Jeff But it's a dry heat!
If you don't know what those settings on all those knobs mean, an oscilloscope is going ot be of limited use.
However, if you don't want it.... (not that I really have much use for one either)
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Being an Electronics Technician, I would take it and use it. However, if you're not familiar with the operation and don't have a friend to show you, it would probably end up being a pretty expensive paperweight (even though YOU didn't pay for it).
About the only use would be to see if there is any ringing on the DCC signal. Clip the test prod and ground lead to each rail. The two volts per centimeter scale should work just fine. The probe might have 1:1 and 10:1 options. Use the 1:1 option. I have done that with a Tek 'Scope. I se a Widow Maker to isolate the 120vac mains from the ground lead.
If there is any ringing, then you can just put a 100 ohm resistor in series with say a 0.1ufd capacitor and put that combination across the end of the buss wires. A few modelers with long buss leads have had to do that. Some decoders do not like excessive ringing in the DCC signal.
Do a Google search for dcc ringing. You will get links that explain this issue.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
If your layout is running OK, you don't need it. If it's not running OK, you probably still won't need it.
Get it and mount it beneath your layout, like under the fascia. Figure out how to look at the DCC waveform, and just leave it set up that way. No one who sees it will ever accuse you of "playing with trains."
A scope is an instant passport to "geek cred."
It takes an iron man to play with a toy iron horse.
Hi!
Graciously accept the meter, play with it, and then sell it on EBAY !
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
Well I guess I 'll take it. I have two friends that can show me how to use it if need be. I have some pretty long buss runs and the best way to make sure they keep working perfectly is to have a piece of equipment ready to help fix it. Besides they are just going to throw it in their recycled electronics dumpster if I don't. Thanks for your thoughts.
richg1998 About the only use would be to see if there is any ringing on the DCC signal. Clip the test prod and ground lead to each rail. The two volts per centimeter scale should work just fine. The probe might have 1:1 and 10:1 options. Use the 1:1 option. I have done that with a Tek 'Scope. I se a Widow Maker to isolate the 120vac mains from the ground lead. If there is any ringing, then you can just put a 100 ohm resistor in series with say a 0.1ufd capacitor and put that combination across the end of the buss wires. A few modelers with long buss leads have had to do that. Some decoders do not like excessive ringing in the DCC signal. Do a Google search for dcc ringing. You will get links that explain this issue.Rich
Just a quick follow-on for anybody who doesn't want to do all that typing (g...o...oo...DOH...backspace...g...l... oh, I give up!)
"Ringing" is a term used in electrical circuits / electronics to indicate either "resonance" or else a "resonant feedback" condition-- an interaction between two or more circuit components-- which could include inductive coupling through the wiring, i.e. picking up "radio noise" like an antenna. Another way to think of it is to consider the microphone feedback squeal you get when a microphone is too close to its amplified output.
Ringing typically appears as a high-frequency, low-amplitude component superimposed onto the main signal waveform. If it is severe enough it could be interpreted by the circuit as a false signal (data). The trouble with ringing is that it can be hard to detect in a constantly changing (dynamic) circuit with arbitrary and/or complex waveforms of varying amplitude, like a radio signal for instance, but in a pure digital situation, such as DCC, the waveforms should be clean and neat with perhaps a little slewing and probably some clipping. No circuit is perfect, so there will always be some amount of ringing-- due to the internal hysteresis present in the circuit-- but that usually isn't a big problem, especially in digital signals, unless its so bad as to broach the digital threshold, through the "no man's land" and spike into the opposing value.
[In a typical digital circuit, you have a "Zero" condition described as one voltage range, and a "One" condition described as another voltage range, and a "Buffer" / No-man's land area which is a voltage range inbetween the two.]
There are two best approaches to dealing with ringing and you can employ either or both-- one is 'snubbing' (or more properly called 'signal attenuation'), which Rich already suggested, and the other is cleaning up the data at the source-- which in this case you probably don't have the access or means to accomplish.
However, be aware that 'snubbing' can (in fact will) in and of itself reduce/eliminate a small part of the signal and signal strength by a small degree (exactly how small is determined by the value of parts you select to build your 'snubber')-- which may introduce a different type of a problem into your system.
Another potential problem though, and one that's in some ways more insidious and yet more likely to occur, is that of "ghost" signals, induced by the DCC wiring and the railroad *track* itself. For large layouts with many off-shooting and parallel branches-- which pretty much any model railroad most certainly is-- the situation can be thought of and described as a complex "transmission" system-- or "induction" system if you prefer to think of it that way. (And truthfully most circuits are transmission systems, its just that at DC or reasonably low AC frequencies, it doesn't matter very much). And when you add a complex varying signal to it-- essentially high-frequency AC-- you can get "inductive loops", "alternative signal pathways", "natural resistance" in the various elements (track, joiners, solder, whatever) that will add up to different values, etc. Each of these "legs" (segments) will contribute some amount to the problem. To top it off, in a decent-sized layout there is enough "track" and associated wiring to amount to being a fairly large antenna-- in both senses really, both receiving "signals" from the environment, as well as radiating "signals" out to the environment.
If you take one pathway-- doesn't matter which one, let's pick the straightest, most direct one, whichever that is-- as the "normal" path, then each diverging or parallel path either "induces" onto a competing "delayed" signal, or else "cancels out" part of the signal-- doesn't have to be a complete cancellation-- think of it as erasing only part of a chalk board at random intervals. Thus modifying the "good" signal that's supposed to be on the "normal" path (track).
If the original signal is strong enough, then it will probably not be too affected by the ghosts / inductions. However, if the original signal is small, or else the "ghosts" are somehow able to be "induced" or "reflected" "hard enough", then they can become competitors to the main signal, or else just muddy it up and make it hard to understand.
Real transmission lines deal with this by either utilizing a "faraday cage" (i.e., Coax cable), or else "crossing themselves" periodically, i.e. "twisting", as in "twisted pair". The faraday cage (coax cable) approach works by completely shielding the signal line by a ground plane that, at least in theory, absorbs external signals that could be induced onto the shield. In practice, its still common for coax cables to also use little snubbers to help out. They just don't need to be as big. Alternately, in a twisted pair scenario, the thinking is that any external influence will influence both pairs equally, thus when they cross, they'll tend to cancel each other out-- and in practice, it works out pretty well, which is why you don't need to string along big ole' coax cables everywhere for your DCC system-- (the CAB Bus, I mean)-- it uses twisted-pairs, a la the CAT5 cabling that your DCC system uses, to naturally supress the external influences.
But you can't realistically "twist" the track or wrap a 'faraday cage' around it. So you're only best hope really is to use a signal with a wide amplitude and moderate frequency range, put lots of filtering on both the transmitting and receiving ends, repeat yourself often, and basically "cross your fingers" and hope everything works out. And fortunately for all of us, it usually does. And there's some additional stuff you can do in the software-level protocols to assist also", but that doesn't mean there can't ever be any problems, only that generally the system is able to figure which signal to pay attention to and ignore any competitors. When you think about it, its actually pretty amazing that DCC works as well as it does really.
"Ghost" (induced" signals) though can also sometimes have a similar effect in the system as "ringing", though the actual voltages induced are less regular and harder to detect. They appear as either extra large momentary amplitudes, or else amplitude drop-outs, as the main signal is combined (either added-to or subtracted-from) with any secondary / competing induced (or external) signals. Again, the primary defense is "repeating yourself often" and "software protocol tricks", but if the situation is bad enough, it can cause a similar, though harder-to-detect, problem.
HOWEVER-- ALL THAT SAID-- it is usually not a big problem-- no tuning required-- because the DCC system *does* repeat itself often and employ software-level protocol tricks to try and ward-off / prevent interference. And it is only in the "noisiest" of environments, electrically-speaking, that either of these conditions is likely to be a problem. And in that event you're already likely to know it since you'll probably have interference also on your TV, telephone, cell phone, or some other thing in your environment (or maybe you won't be able to call out, or else will have areas of drop-out).
Oh, and by the way, here's a couple of google / wikipedia links to save you from all that typing:
Ringing:
http://en.wikipedia.org/wiki/Ringing_(signal)
Ghosting:
http://en.wikipedia.org/wiki/Ghosting_(television)
Hope this helps.
John