In short, [Christer] needed a high-frequency active differential oscilloscope probe, and they’re not cheap. So he built one himself. With some minor tweaking on the input damping resistors ...

but he needed a way to pick up the fields and feed them into one of the scope’s probes. He ended up building this EFM probe dongle to accomplish the task. He admits that this isn’t much more ...

Impedances are shown for three different probes. Note that 10 pF is pretty common for decent probes; better ones, like Tektronix’s very nice 5 pF TPP1000 approach a thousand dollars. Agilent recently ...