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Agilent 1152A active probe "smartprobe" conversion for DSOX3000 series scopes
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jjoonathan:
Yep, reflections between SA and probe were the issue, classic trap for new players. I wasn't previously aware of how poor the 50 ohm termination on my signal hound was. Here's the response of the probe on a SA with slightly better termination, note that the ripple easily halved and now agrees much better with TheSteve's measurements. Adding a 3dB attenuator between probe and SA (not pictured) didn't reduce the ripple further. I didn't try multiple lengths of cable to see if the ripple width changed, so I can't (yet) properly assign the remaining ripple to probe vs attenuator.

The remaining distinction between TheSteve's probe and my probe seems to be bandwidth: my 54701A looks more like a 2GHz probe, and TheSteve's 1152A looks more like a 3GHz probe, even though they're both nominally 2.5GHz. I still don't entirely trust the 50 ohm terminators I'm probing, one is no-brand and one is home-brew, so maybe they're a bit heavier at 2.5GHz? If so, they both give the same results.
Bud:

--- Quote from: jjoonathan on March 15, 2017, 04:52:15 am ---I wasn't previously aware of how poor the 50 ohm termination on my signal hound was.

--- End quote ---

Thanks for acknowledging that. I was asking for years why signal hound did not specify input return loss for their doggy product since it came out, though I think I knew the answer.
TheSteve:
The termination I used/probed is a SMA jack with three 0603 150 ohm .1% resistors soldered to it. It tests out pretty decent to 6 GHz and is easy to probe as the resistors are exposed.
rx8pilot:
This is an interesting thread.... looking for some project probes now :-)

Sent from my horrible mobile....

TheSteve:

--- Quote from: rx8pilot on March 15, 2017, 07:19:23 am ---This is an interesting thread.... looking for some project probes now :-)

Sent from my horrible mobile....

--- End quote ---

Active probes rock - especially when they are cheap.
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