Scope Probe Test Jig

This video demonstrates a simple test jig that can be used to identify the loading that a probe (e.g. Scope Probe) can have on a circuit. The test jig is configured for 50R (with 0R resistors in series).

In this video the impact of a scope probe is measured using a 50R signal generator and a 50R spectrum analyzer. The scope probe loading is significant at higher RF frequencies (about 3dB at 50-60 MHz)

The loading is more significant when the circuit being probed has a higher impedance at higher RF frequencies. This can be demonstrated by replacing the 0R resistors with larger resistors (e.g. 1K, 5K, or even 10K). However, when you use larger resistors you will be introducing an impedance mismatch and forming a voltage divider. There will be significant attenuation from the jig BUT when a probe is attached the attenuation will be much greater. Focus on the relative measurements between no probe connected and probe connected.

There are many videos and tutorials that explain why scope probe's impedance varies with frequency and the explanation if out of scope for this video.