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Old 10th Jul 2020, 12:48 pm   #47
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Default Re: Hi-Z input probe by Bob Pease.

Hi!
I had a quick look at that and the associated threads - yes, it does look interesting. On account of the pressure I'm currently under - lots of urgent things demanding my immediate attention - I'll have a further in-depth look when I can.
However, having said that, the essential problem with any probe is its input capacitance and the ability to make a very low inductance connection to the 0v. / gnd. reference point when it is in use. An input capacitance at the probe tip needs to be not more that 1 pF and an inductance not more that a few nH for use with high-Z sources. It's more than component selection that is important: physical layout and mechanical construction is also very critical. The only ones I've seen that come anywhere near the 'ideal probe' are made by Tektronix - and they are exceptionally expensive!

Al.
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