Products > Test Equipment
> 1 GHz DIY differential probes
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Marco:
High resistance at low frequency, high enough impedance to still be useful at high frequency. So still useful for general purpose probing in a pinch.

The really high frequency differential probes all try to be constant impedance, just high enough to not fuck a 50 Ohm line too much ... and that's all they are useful for.
BravoV:

--- Quote from: Mechatrommer on October 16, 2018, 11:09:31 am ---can we make 100fF?

--- End quote ---

Femto farad ? I'm guessing its not that easy, example of a 3 decades old, HP 54701A 2.5GHz active probe (not a differential probe) has 0.6pF (typical) with input resistance of 100K Ohm.

Rerouter:
If you want crazy low input capacitance, things get complex, but I would guess we can reduce what is currently there and iterate towards the goal, anything under 0.5pF already appears to be crazy level money,

Most of the schematics I have glimpsed in the past from reverse engineered crazy high bandwidth probes seemed to use an input network to cancel out the apparent capacitance. and pretty much no protections at all.
Gerhard_dk4xp:
I absolutely LOVE these HP probes, also the 1152A successor!
The 0.6pF make the series resonance of the ground lead much less important
and you can probe around without fear of burning sth. @ less than 50V.

regards,
Gerhard
Mechatrommer:

--- Quote from: BravoV on October 16, 2018, 11:32:57 am ---
--- Quote from: Mechatrommer on October 16, 2018, 11:09:31 am ---can we make 100fF?

--- End quote ---
Femto farad ? I'm guessing its not that easy, example of a 3 decades old, HP 54701A 2.5GHz active probe (not a differential probe) has 0.6pF (typical) with input resistance of 100K Ohm.

--- End quote ---
sorry i screwed up (msg deleted) i didnt see the low-f respond (1st attachment). so 1pF seems feasible? i got 0806 smd 1pF here ;D (2nd attachment) they both load the 500 ohm node by a bit anyway @ 1GHz ???


--- Quote from: Rerouter on October 16, 2018, 11:44:20 am ---anything under 0.5pF already appears to be crazy level money,

--- End quote ---
how about pcb printed capacitor? or diy like 2 plates separated by a piece of paper? is it wrong to be unacademical?
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