To test the rise time of oscilliscope probes, I made a simple circuit with fast SMD TTL inverters:
The resistors of 5 inverters in parallel provides an output impedance of approx. 220 ohm/5 = 44 ohm plus the dynamic output resistance of each gate output.
The double layer PCB design has electronics on top side and the BNC connector on bottom side:
A battery clip for a 9V block battery is used to provide power for the 5V regulator:
Adding a 50 ohm BNC load:
With 50 ohm load, frequency measurement. The output high signal is slightly above 2.5V, that is, the 5 inverters with resistors provides a total resistance slightly below 50 ohm during the voltage division taking place.
Rise time measurement , Keysight DSO-X2012A 100 MHz scope with a 150 Mhz passive probe:
Rise time measurement , Keysight MSO-X4054A 500 MHz scope with a 700 Mhz passive probe:
Rise time measurement , Rigol DS1054Z 100 MHz scope with a PVP2150 150 Mhz passive probe:
Rise time measurement , Rigol MSO5074 350 MHz scope with a PVP2350 350 Mhz passive probe: