Question related to Oscilloscope HV probes

[MathWizard]

I have the Hantek 100x probes. Now that I have a good functino gen, I should compare all my probes, but I don't have real coax, or accesories like terminators yet......I should order some next week.

[Frank_MV]

Hello,

Today I adjusted my new Testec TT-HV250 probes.
At NF I can adjust a good square wave signal, but at 1MHz you can see clear overshoots with all my 3 probes.
Now I think about whether I should keep them or exchange them.
Maybe a Staeubli probe does better here ?

What do you think ?

It has been mentioned here before, but I have now also noticed that when I touch the red BNC connector of the probe, I can see clear interference that overlays the measurement signal.

Br,
Frank

[David Hess]

What do you think ?

That is the result I would expect if the ground lead is too long.

[bdunham7]

What do you think ?

It has been mentioned here before, but I have now also noticed that when I touch the red BNC connector of the probe, I can see clear interference that overlays the measurement signal.

Once you connect test leads, probes, whatever, they become part of your circuit.  Here you have some ~150MHz ringing.  It doesn't mean you probes are 'bad', it just means that your new circuit has some ringing--perhaps for the reason David Hess mentions.  Once you start getting up into these frequencies, things start getting trickier.  As for touching the BNC, I'm not sure why it would be that touchy, but perhaps there is some issue in your whole ground setup.  Post a photo maybe?

[Frank_MV]

Enclosed is my measurement setup. It is only the calibration of my HV probe at 1MHZ at my RTB2004.
Am I possibly doing something wrong ?

[bdunham7]

Enclosed is my measurement setup. It is only the calibration of my HV probe at 1MHZ at my RTB2004.
Am I possibly doing something wrong ?

Do the probes included retractable test hooks?  I would try using a test hook and removing the ground lead entirely, as in not attached to the probe or the scope.

[Frank_MV]

Yes, retractable test hooks is included but nothing changes.
The overshoot becomes smaller when I touch the test cable with my hand.

[Frank_MV]

My Rohde & Schwarz probes still have 2 additional adjustment trimmers for RF compensation but the Testec has this trimmers not.

I still have a week to replace these probes at my distributeur - but which ones ?
I need HV probes for my tube amps

[tggzzz]

Enclosed is my measurement setup. It is only the calibration of my HV probe at 1MHZ at my RTB2004.
Am I possibly doing something wrong ?

The only thing that matters is the transition time; the period is completely irrelevant.
https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/

If the probe has, say, a 15pF tip capacitance (C), and your ground lead is 150mm long (i.e. ~120nH inductance (L)), then the LC will resonate/ring at ~100MHz.
https://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/

The solution is to either reduce the tip capacitance (difficult!) or have a shorter ground lead (easy).
https://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/ but there are other techniques.

Also work out the impedance of 15pF at 100MHz, and you will see your "high impedance" probe is not high impedance

[tggzzz]

This time I only used the ground cable for the connection to the oscilloscope, and it looks the same as yours.

Yes, that ringing is to be expected, for the reason I gave in my previous post.

[bdunham7]

Yes, retractable test hooks is included but nothing changes.
The overshoot becomes smaller when I touch the test cable with my hand.

Is that with no ground lead installed?  OK, then if you have the little groundspring attachment, try that.  Otherwise, if you can hold the probe so that the tip is on the calibrator output and the exposed ground shield part is on the ground, you should be able to eliminate that ringing. If not, then IDK what's going on.

[Frank_MV]

There are new findings. I took a look at the accessory bag of the HV250 - unfortunately it doesn't say anywhere what it is needed for.
So I just combined and tried it. The protective cover of the probe can be removed and I pushed the metal sleeve over it, so I don't need a ground cable anymore - so the ground connection is shorter.
And what should I say, there are no more overshoots at 1MHz rectangle - it's really the ground cable.
But is this still a real use case ?
For measuring in circuits I always need a ground wire with clamp.