[Question] Oscilloscope Probe Bandwidth

[PixieDust]

Hi, I watched this video:



In it, there's mention of a rule of thumb that oscilloscope probes should be x1.5 the bandwidth that you're testing. There's talk of "System Bandwidth". It's all fair enough.

What I don't understand is why are oscilloscopes of say 100MHz sold with 100MHz probes then? Shouldn't they come with 150MHz probes? Or are 150MHz probes simply marketed as 100MHz, but in reality they are 150MHz probes? But in the video, it specifically says that if you need say a 1GHz scope, you should be using a 1.5GHz probe! Confused .

[tautech]

Probe BW doesn't roll off a cliff and can easily do 50% beyond rated BW.
A few years back there were concerns if 100 MHz probes were still suitable to be used with a 200 MHz hacked DSO.

A member swept a few probes and graphed them and the 100 MHz one was barely 1dB down on the 200 MHz rated one.

As the industry determines frequency rating by a -3dB rolloff there is a generous margin before any part of the measurements system fails to meet its BW rating and then there's also instrument accuracy rating to also consider......some +3%.

[PixieDust]

Many thanks .

[noisyee]

It's meaningless to specify bandwidth alone for a high impedance passive voltage oscilloscope probe. In fact, they are already specified as system bandwidth.
A specific oscilloscope probe will only fit certain oscilloscope. Passive probe relay heavily on compensation to achieve target bandwidth, which is related to a certain front end circuit.
Here is how LeCroy said on their website:

Each passive probe is recommended for a certain oscilloscope, using the right passive probe with the right oscilloscope means that the probe will be properly compensated across the entire bandwidth. Using probes with a different oscilloscope will only let you compensate for low frequencies.

For most brand, you can find a probe compatibility list on their website or probe datasheet.
To my own experience, a keysight compatible 500 MHz probe will have strange frequency response above 50 MHz on a LeCroy, Tek, or Siglent.

[PixieDust]

I have a 2 channel analog scope that didn't come with probes. Ended up going for two pairs of CalTest x1 and x10 probes. I had no idea probes were so finicky!