Paulo Oliveira was experimenting with probing high speed signals with his oscilloscope. You might think that a 500 MHz probe would be adequate to probe a 125 MHz clock signal, but he demonstrates why this is not the case. He wrote a detailed article on building your own high-speed oscilloscope probe, demonstrating how a surprisingly simple and affordable DIY passive probe can outperform even the best 10X passive probes for this particular application.
You can read his observations and probe construction details on Paulorenato.com.
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