Does any system actually do that? Digitrax certainly doesn't.
This is flat out wrong. Decoders assume that the previous instructions stand until they get an update. If dcc commands stop going out on the rails, the trains will happily keep running unless you kill power. You've never had any runaway trains? It definitely happens.
Not sure what point you're trying to make. This is kind of a dumb message thread anyway. *
Give the man a coconut, zero frequency is indeed a special case. Now find a railway power supply that puts out a perfectly smooth DC waveform.
Bullshit. If current only flows in one direction out of the supply then the current does not alternate.
Bullshit. See above. Guy
A car battery. Perfectly smooth 12v. DC.
I think you'll find it reduces over time, initially in a fairly linear way and later definitely non-linear. Guy
Not bullshit at all, the DC component may only cause current to flow in one direction, but the transitions will cause currents at frequencies above DC to flow in both directions, they may, or may not, be smaller than the dc current but they do exist and do flow in both directions.
Jeff
Yes, bullshit. Either that or there is effectively no such thing as a DC power supply. Guy
Depends if you recharge it between operating sessions or not.
NO. For the purppose of analysis you can split any signal into components. Those components do not exist in isolation in the composite signal.
Tell me, how do the electrons and holes in the wire know which frequency component they are associated with and which way to flow?
MBQ
Fuck me, where do people get their DCC "knowledge" from? Try reading the specs. Specifically RP-9.2.4 section C. If you choose cheap decoders that don't implement the spec correctly, or disable the timeout then you deserve every run-away you get.
The point that there is always *something* even if it's just the preamble on the rails. It is neccessary to continue delivering power.
You didn't raise the level, so why did you bother replying?
MBQ
I suppose you could take that view if the DC level changes or you switch the DC voltage on and off. At the time of the transition there will be AC components generated. However, it would be silly to classify a DC power supply as AC merely because of short AC transients caused by varying the voltage or switching on and off, but in the case of DCC the AC components are there *all of the time* and make up the characteristics of the signal, ie the pulses. Without the AC parts the DCC waveform could only be just a constant DC level.
Jeff
Decoders see a DCC signal not an AC signal otherwise they would not be able to decode the commands. For non DCC locos on a DCC layout they see PWM by stretching one's or zero's depending on direction to move the loco. So you could argue its almost DC in that instance and almost AC with no DC locos.
Note that Hornbys Zero 1 system of the 1980's was very much as you describe an AC supply with control data overlaid where as DCC is the supply and signal combined. What this means for the modeller is that if the supply voltage gets to the decoder so does the commands and everything works. Whereas the Hornby system was not as reliable as the supply voltage might arrive but the commands sometimes got lost.
Not really, no. It's a lot smoother than rectified DC but the voltage will still fluctuate, and will go down as the battery discharges. Guy
You have described AC in a way that will necessarily also encompass pretty much every DC power supply on the market. This has put you in your normal position of being the only one marching in step.
Enough of your sophistry. Guy
On
You very conveniently snipped the next part of the post that said "it would be silly to classify a DC power supply as AC merely because of short AC transients caused by varying the voltage or switching on and off".
With a conventional DC power supply (not DCC or PWM) any AC components make up a small part of the output. With DCC if you remove the AC components all that you are left with are 2 DC levels +V and -V which cancel each other out to zero!! You cannot switch between to 2 DC levels without the AC components, they are there all of the time and are real and form the major characteristic of the signal i.e the data.
Jeff
Yes, because that was the point I originally made and which you were apparently disputing. Since you'd accepted my point but were continuing to argue that you're right and everybody else wrong I did not see much point continuing. Guy
I think the problem here is one of perception, the problem seem to be that this is being viewed from the point of view of a motor control system rather that the general view of how to classify a signal. If the DCC waveform, or any other pulse waveform for that matter, was being used in any other electronic application as a means of sending data down a wire, there is no way that it would be considered as being DC, even considering the dual purpose of the signal (ie conveying data as well as a power source after rectification).
Getting back to whether you can classify slowly changing DC or slow on and off switching of DC as an AC signal, it depends on your point of view and what information you are trying to recover. If you view it over a long enough time period then you can recover AC information, the long integration period being a way to improve the signal to noise ratio of your measurement. So to one person a slowly changing level or slow on/off is a DC signal, but to another it is AC data. In a model rail application it is obviously viewed as DC.
Jeff
Have you bothered to read the rest of the thread? We've already established that DCC *is* AC. The DCC signal is rectified to produce on board DC power for the electronics and motor. The data is then decoded by looking at the signal before rectification.
Wrong again. only zeroes are stretched. It's still AC,but with a positive or negative DC offset, depending on the desired direction.
No, it's always AC.
MBQ
If there are no stretched zeroes then DCC is nominally a perfectly balanced signal and there is no DC component. Remove the AC components and you are left with nothing.
If stretched zeroes are being used then you will have either a positive or negative DC component depending on the direction the unchipped loco is being driven. You clearly can't have both at the seame time.
MBQ
No one (apart from you, or was that a typo?) is considering DCC to be DC. DCC is AC.
MBQ
Read the first review of Hornby Zero 1 system in MRC, was well ahead of its time, quite amazing really.
Cheers, Simon
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