oscilloscope input impedence?

[tom]

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

 

[Andrew Holme]

tom wrote:

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

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.