Scope probes

[pkane]

That's a much longer rise time. Here's my scope's built-in AFG with the TPP0500B probe showing a rise time of about 4 ns:
View attachment 53712

So it’s the generator fault.

 

[Dimitri]

proof that no cable can fix a bad source

 

[sergeauckland]

I doubt your cheap probe can measure a rise time of less than 2 ns, which is what we're looking at here. The distortion is probably the result of interactions between the probe capacitance, source impedance, and PCB + probe ground inductance.

No, especially as my 'scope has a bandwidth of 40MHz, but what I do not understand, and that's my fault, is what's the point of this thread?

S

 

[pkane]

but what I do not understand, and that's my fault, is what's the point of this thread?

S

Cables matter?

 

[LTig]

No, especially as my 'scope has a bandwidth of 40MHz, but what I do not understand, and that's my fault, is what's the point of this thread?

Have fun? Remember the motto of ASR?

 

[mansr]

what's the point of this thread?

I thought someone here might find it interesting. Feel free to ignore it. I won't be offended.

 

[LTig]

Found a better source: SPDIF output of RME ADI-2 PRO fs. Not terminated with 75 Ohm though, this may explain the ripples.

50 ns/div:

5 ns/div:

A risetime of 5.5 ns is not too bad. Still unknown whether the probe or the source is the limit though.
EDIT: spec of the probe is 1.75 ns risetime.

EDIT: same signal with same probe in 1:1 instead of 10:1, 50 ns per div:

Now we know why we should not use probes in 1:1 for high bandwidth signals.

 

[LTig]

I thought someone here might find it interesting. Feel free to ignore it. I won't be offended.

I do. Keep posting.

 

[Deleted member 2944]

Scope probes can be a little confusing at times. When to use one....and when you don't need to......and how you can get confused by the results.
Dave has an illustrative video on this topic:

Dave.

 

[mansr]

Found a better source: SPDIF output of RME ADI-2 PRO fs. Not terminated with 75 Ohm though, this may explain the ripples.

50 ns/div:

View attachment 53715

5 ns/div:

View attachment 53716

A risetime of 5.5 ns is not too bad. Still unknown whether the probe or the source is the limit though.

How are you grounding the probe? It can make a big difference to things like those ripples.

 

[LTig]

How are you grounding the probe? It can make a big difference to things like those ripples.

The ca 10 cm long wire. You're correct, I should try something shorter ...

... done: using the supplied spring, 50ns per div and 5 ns per div, the ripples are mostly gone:

 

[sergeauckland]

Have fun? Remember the motto of ASR?

Ah, you're having fun? Now I understand, I think.



S

 

[RayDunzl]

Why can't we use an electron microscope to see what the electrons are up to?

 

[DonH56]

I thought about digging up a shot from work showing <20 ps edges on a 70 GHz DSO, or the edges from one of our 30 GHz (slow) dif probes, but then remembered this is an audio forum...

 

[NTK]

I thought about digging up a shot from work showing <20 ps edges on a 70 GHz DSO, or the edges from one of our 30 GHz (slow) dif probes, but then remembered this is an audio forum...

This probe?

 

[mansr]

I thought about digging up a shot from work showing <20 ps edges on a 70 GHz DSO, or the edges from one of our 30 GHz (slow) dif probes, but then remembered this is an audio forum...

Sounds expensive.

 

[DonH56]

This probe?

View attachment 53741

Yup. We have a number of them, along with the earlier 25 GHz version. And a ton of other probes as well, natch.

 

[DonH56]

Sounds expensive.

I don't remember the cost of the tri-mode probes, think ~$20k to $30k each.

I've said before I can check out a DSO (with or without probes) and take it home to play, but balk at taking home a 'scope worth more than my home.

 

[mhardy6647]

Too lazy to read? It's written at the bottom of each screenshot: 24.5758 MHz.
...

Derp. Sorry.
I saw that, but misinterpreted.

I guess I was thinking/wondering/assuming it was an audio-frequency square wave, and I was pretty disillusioned to see expensive probes (or even cheap ones) struggling to reproduce it (umm, I guess, transfer it would be more apt).

 

[sergeauckland]

Derp. Sorry.
I saw that, but misinterpreted.

I guess I was thinking/wondering/assuming it was an audio-frequency square wave, and I was pretty disillusioned to see expensive probes (or even cheap ones) struggling to reproduce it.

I missed that too, but my excuse is that I've never used a digital 'scope, so those numbers at the bottom meant nothing to me. My first 'scope was a Cossor 1049 with a 100kHz (not MHz or GHz) bandwidth, http://www.thevalvepage.com/testeq/cossor/1049/1049.htm so even my current 40Mhz 'scope seems advanced.

S