I think you should leave alone the 7Axx inputs, they are perfectly
fine as they are ;-)
(I say this because this is not like the 222 probe issue where the
probe is non-standard and hard to get, Tek probes are plentiful and it
should be possible to swap the HP ones for the right ones).
In any case, making a compensated attenuator is not easy as soon as
you get into three digit Mhz. I tried once and my homemade probe
turned out quite rotten.
ST
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On Thu, May 28, 2009 at 9:10 PM, John Griessen <john@...> wrote:
Geoff Blake wrote:
If you have a 'scope with input impedance of say 20pF in parallel with
1Meg, putting a parallel resistor capacitor of 1Meg/20pF in series with
the input (exactly the same as an input normaliser) will change the input
capacitance to 10pF, and resistance to 2Meg.
It will also upset the calibration...
Hmmm...the voltage would be divided down. ?Using these as 100:1 probes would be good. Time to do some RC calculations considering
the attenuator values in a 7A26 for instance. ?I have maybe 7A26's that came with scopes I bought...
A pair could be dedicated to these probes. ?The rest of the amp may not be fast enough though.
Maybe I need to ask on the HP list about favorite 9 pF scopes. ?:-)
John Griessen
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