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Passive probes and quality

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David Hess:

--- Quote from: JacobPilsen on November 07, 2024, 07:35:01 pm ---In short: Always take the better probe if you can.

The probe attenuation is combined with the oscilloscope input attenuation.
When both have -3dB at 50MHz, they will have about -6dB together. And they will have -3dB somewhere lower, for example around 43MHz.
But a 100MHz probe with a 50MHz oscilloscope will have -3dB closer to 50MHz, for example 47MHz.

Some literature: https://w140.com/tekwiki/images/6/62/062-1146-00.pdf
(Tektronix Oscilloscope Probe Circuits Concepts by Joe Weber)
--- End quote ---

That is true, but only to a limited extent.  Oscilloscopes and oscilloscope probes are not specified by their individual -3dB points.  Instead, the specified bandwidth is the combined oscilloscope and probe bandwidth at the probe tip.  The specified probe bandwidth is more like the bandwidth up to which the probe will perform properly, without excessive distortion or aberrations.

If I have an oscilloscope with a specified bandwidth of 50 MHz, and an oscilloscope probe with a specified bandwidth of 50 MHz, then my testing at the probe tip with the proper source (see below) had better reveal a bandwidth of at least 50 MHz.

Note however that for objectivity, these specifications are generated using a *terminated* 50 ohms source, which is 25 ohms.  A higher impedance source, like most circuit test points, will have lower bandwidth because of interaction with the probe tip capacitance.

hp3310a:

--- Quote from: tszaboo on November 07, 2024, 09:45:51 pm ---The 70MHz 12 bit Siglent scopes come with 200MHz probe. If you accidentally overclocked the oscilloscope to 200MHz, you don't need new probes.

--- End quote ---

I was looking forward to being pleasantly surprised, but unfortunately that isn't the case. The brand new SDS804X-HD that was just delivered contains PB470 70MHz probes (4 pieces).

tszaboo:

--- Quote from: hp3310a on November 29, 2024, 11:59:18 am ---
--- Quote from: tszaboo on November 07, 2024, 09:45:51 pm ---The 70MHz 12 bit Siglent scopes come with 200MHz probe. If you accidentally overclocked the oscilloscope to 200MHz, you don't need new probes.

--- End quote ---

I was looking forward to being pleasantly surprised, but unfortunately that isn't the case. The brand new SDS804X-HD that was just delivered contains PB470 70MHz probes (4 pieces).

--- End quote ---
Yes, that's what they write on the side of the probe.
It was measured to be way faster than that.

hp3310a:

--- Quote from: tszaboo on November 29, 2024, 12:01:06 pm ---
--- Quote from: hp3310a on November 29, 2024, 11:59:18 am ---
--- Quote from: tszaboo on November 07, 2024, 09:45:51 pm ---The 70MHz 12 bit Siglent scopes come with 200MHz probe. If you accidentally overclocked the oscilloscope to 200MHz, you don't need new probes.

--- End quote ---

I was looking forward to being pleasantly surprised, but unfortunately that isn't the case. The brand new SDS804X-HD that was just delivered contains PB470 70MHz probes (4 pieces).

--- End quote ---
Yes, that's what they write on the side of the probe.
It was measured to be way faster than that.

--- End quote ---

So what you are saying is they make one probe with different labels, just like with the scopes?

tautech:
https://siglentna.com/wp-content/uploads/dlm_uploads/2024/11/Probe_List_11262024.pdf

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