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Old 19th Jun 2020, 10:48 pm   #45
G0HZU_JMR
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Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
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Default Re: Hi-Z input probe by Bob Pease.

Quote:
When you refer to 'faster transistors', I assume you're referring to the BJTs.
Yes, but I think I worded it poorly. What I meant was that you are using faster transistors than the original 2N3904 and 2N3906 BJTs and that might explain why you are seeing a better waveform with minimal ringing.

I did try my copy of the original with a square wave drive and fed the output of the probe to an unterminated scope via a short run of RG58 coax. I did see some ringing but I'm using the original 2N3906 PNP BJT at the output. Since that test I've fitted a x10 scope probe to the scope and then connected the tip of the x10 probe to the Pease probe output using a scope tip to BNC coaxial adaptor. This seems to work a bit better although it still struggles a bit once the waveform gets above about 2Vpkpk.
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