Question on high-bandwidth DIY 21:1 scope probes

[comfortcube]

I've seen in more than a few places now something like this: http://jahonen.kapsi.fi/Electronics/DIY%201k%20probe/

In the places I've seen, it's always a 1k or 950ohm in series with the source, which gives 21:1 or 20:1 division when the scope input is 50ohm terminated. However, I'm just wondering if there's good reason to this choice of ratio? Like say 20:1 division would be too much for the signals I'm looking at and I don't have a low-noise pre-amp at hand (can be made ofc) - then would say a 10:1 ratio work - i.e., 450ohm instead of 950? Or 50ohm, to get 2:1? Or what about just straight probing with no discrete resistances other than the 50ohm terminator?

I'm guessing the biggest factor here is loading of the source? And 950ohm/1k is kind of a balance between loading the source and voltage division ratio?

[iMo]

A discussion on it is here
https://www.eevblog.com/forum/projects/cheap-wideband-121-oscilloscope-probe-for-logic-signal-applications/

[David Hess]

450 ohms for a 10x probe has a load resistance which is a little too low for most applications and 4950 for 100x has too much attenuation and problems with compensation, so 20x is a better choice if the weird multiplier is acceptable.

[comfortcube]

Oh I gotta get better at searching! I had tried "DIY scope probe" and "DIY high-bandwidth probe" but couldn't find what I was looking for. Maybe I was blind too, that's entirely possible. Thanks!

[tggzzz]

Oh I gotta get better at searching! I had tried "DIY scope probe" and "DIY high-bandwidth probe" but couldn't find what I was looking for. Maybe I was blind too, that's entirely possible. Thanks!

There are links to a few other DIY probes here: https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/