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Does a capacitor charges smooth, or in stairs?

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rhb:
There is *nothing* wrong.  Take a look at the photo of the short piece of RG402 with no connector at the end.  That's the circuit.  It's a series resistor and capacitor using transmission line for the capacitor.  There isn't any place to connect the sampling head at the far end of that short piece of RG402.  If it were connected there wouldn't be a +1 reflection coefficient and thus no stairstep.

The signal is a 250 mV, 200 kHz square wave with a <20 ps rise time.  The sampling head has a <15 ps rise time.    Look at the time scales.

The SD-24 head generates a square wave and displays the outgoing and reflected signal appearing on the input.  The first big step is the outgoing pulse.  The 2nd big step is the reflected pulse from the open circuit at the end of the transmission line.  The staircase is a bit of rounding of the edge of the open circuit reflected step as the signal bounces in *just* the coax.  The large steps are the delays in the sampling head circuit getting to the 3.5 mm input connector and back.

This is basic time domain reflectometry with a high end instrument designed specifically for the task.  As I suggested before, find an app note on TDR.  It will be quite educational.  I've had more fun with the 11801 & SD-24 than any other instrument I've bought (except guitars and harmonicas ;-)

Have Fun!
Reg

Labrat101:

--- Quote ---RoGeorge
  Wow, the cleanest stair-steps reflections I have ever seen!   

--- End quote ---

You are all chasing a Rabbit down a Hole.
Sending a pulse or a signal down a coax ,
50 ohm or what ever.  That is not terminated the signal has to go some were .. so it will go backwards.  Echo . So there will be a reflection.
There will be a time difference.  There fore you will see steps .  SWR will not be 1:1 on any open Transmission line .
  Pulse . or Square wave . is made up of all waves . and hence it will break down back to a sine.
  There is only one true wave form and it a sine ..  That why light can't go round corners .without
Reflections  call what every you like but its the same.
It's like ripping water when a ripple gets to an edge it bounces back.  Whether you see it or not it's there..  And there is never a square wave in Water .. or light etc. etc.
Only thing at the bottom of a Rabbit hole is ... :horse:   €¥)^(¿

Also Notice How the original Author Who Himself said it was Only practical on paper.
 As for all Us Nerds . including myself . .
 Paper theories are very good as long as they stay in the right place . 
  You can always work it out with a pencil ... but taking medicine will also work .. :) 

 PS.  one nanosecond light travels about 0.3 meters measure the distance between the steps
     and you will find the refection point in your coax . or the the dialectic failure point .
     if the coax is perfect with no defects it will give you the length of the coax being tested.
     A tape measure would also work without the complications.
      This Method is good for finding bad connections in long data lines and has a high accuracy
      to locate the damage section of cable and repair it . used it myself to find bad broken  transmission line .. . but it does not prove that a Capacitor charges in steps .
   it like a saying a fish does not breath air . No it removes it from the water (H20.)

   Still a large Rabbit Hole ..


rhb:
I received a Rigol DS1202Z-E today.

First the full step response using one of Leo Bodnar's <40 ps 10 MHz square wave generators and a 50 ohm thru termination.



Then a vertical zoom on the upper edge of the step:



What's really significant here is that Rigol is dithering the sampling clock and the jitter is under 100 ps so it shows a <100 ps step quite clearly.

That in turn implies that the AFE has a *real* BW of 3.5 GHz!!!

Have Fun!
Reg

StillTrying:
The steps are 1ns apart so it's just some sampling thing. :) What's it triggering on 12 screens away.

This Siglent pseudo ETS DOTS mode shown by rf-loop looks interesting.

https://www.eevblog.com/forum/testgear/siglent-1104x-e-or-2204x-e/msg2118325/#msg2118325

I don't know if it still works with 500MSa/s on a fast edge.

rhb:
If the sampling is dithered at 100 ps intervals, then the result is *exactly* what one would get of an AFE with >1.75 GHz BW and no anti-alias filter. 

Whether that is the case or it is some mundane programming error is unknown at present.  But it very much looks to be sample time dithering rather than a programming error.  I do *not* get the same result from my DS1102E with the same setup.

rf-loop's post is  meaningless.  There is no indication of the actual input waveform.  I'm using a *well* vetted signal source.  My <40 ps pulser came with a CSA803A & 40 GHz SD-30 sampling head step response plot showing a 37 ps rise time.  I can easily feed the <20 ps 11801 calibrator  pulse to the Rigol.  It won't change the result.  I've used the Bodnar step generator to test my  1 GHz Tek 7104 analog scope.  And it shows a <350 ps rise time.

In short, I have a wide range of hammers from an ounce or so to 30 pounds.  So I can beat on things rather hard.  Naturally I don't smack electronics test gear with a 30 pound stone boat, but I have the electronic equivalents.

Please look at my posts to the thread RoGeorge started.  The 11801 & SD-24 were *very* expensive kit in the early 1990's.  If you think those are erroneous you need to try harder.

Have Fun!
Reg

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