oscilloscope input impedence?

Dec 06, 2004 1 Replies

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tom 21 years ago

I've got a real dumb newbie question so bear with. I'm running some interconnected amplifiers ect with the required 93 ohm coax for the modules but I want to monitor the signal on my scope which has a

1megaohm input impedance. Now I know the scope is designed to not load the circuit being tested by having a high input impedance but doesn't that cause a big reflected voltage signal and thus a misread of the real voltage ? Or does the scope somehow compensate or do I have it wrong? Thanks. tom

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Andrew Holme 21 years ago

Connect a 93 ohm dummy load across the last output and connect your x10 'scope probe across that.

For the ultimate in fidelity, twist some fine wire around the shield right at the end of the probe and use that as ground instead of the normal probe earthing lead. This makes a _big_ difference at high frequencies. When looking at a 1 MHz clock, for example, all the ringing, overshoot and undershoot disappears.

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