Hello Kurt,
well, my point is that I do not see any contradiction here.
When it comes to switchable 50 Ohm/1 Meg-Ohm inputs, I am only familiar with the input attenuators of Tek 24xx o'scopes.
In those, the input-R-Termination to GND changes between 50 and 1 MegOhm through switches, but it all ends up in the same pre-Amp circuitry...
And, I would not expect the cap load of the 50 Ohm and the 1 MegOhm input settings to change that much when switching between them.
I would be seriously surprised if your new Agilent scope uses a much different input attenuator circuit, as far as the 50 Ohm/1 MegOhm switching is concerned.
Allow to ask how can we make sure that the TCPA amp fulfills the classic R scope x C scope = R probe x C probe equation for a compensated probe input?
What does the output stage of the TCPA look like and what is the estimated load of the BNC cable?
I would add a small cap with some few pF to the o'scope inputs - just to see, if that results in any changes.
Other Opinions are encouraged...
Good Luck,
Magnus
