I'm probing an RF (~75 MHz) oscillator. I'm trying to measure the voltage drop across a capacitor. (I'm afraid I may be pushing it's limits.) When I attach my x10 'scope probes it loads down the circuit some. (C probe = 16pF) Can I add a series capacitor (1-2 pF) to make another voltage divider and turn my probe into ~ x 100 (I'll have to calibrate it from another stiff source.)
Edit: So I tried it. Massive fail on the first attempt because of the inductance in the long ground lead of the probe… (long is ~10cm). I made a little ground clip. And soldered it on.
And that worked better.
Here's the 'scope shot with x10 probes top and bottom of the 2.2 pF cap that I have in series.
Channel 2 (in blue) is the "x100" side. I'm getting what looks like more bandwidth with the x100. This is not too surprising the x10 probe is an HP10071A Bandwidth = 150 MHz. But also the calibration factor is only about x30. 20 Vp-p vs. 7 Vp-p… Is that to be expected?
Best Answer
You can use a piece of paper or something similar, i.e. thin and non-conductive, like scotch tape. Place one piece over a ref.source and another one over the test point, then measure as usual and compare.