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| Probe into probes. What's up? |
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| bdunham7:
--- Quote from: srb1954 on February 01, 2023, 12:50:46 am ---I don't know what terminating load the Bodnar pulser requires but the conditions for verifying probe performance traditionally calls for a 25 \$\Omega\$ source (ref. Tektronix Circuit Concept series, Oscilloscope Probe Circuits, p27). This source impedance is typically made up of the pulse generator source impedance of 50 \$\Omega\$ paralleled by a 50 \$\Omega\$ through termination. So even if you are not using a interposing cable the output of the pulse generator still requires a terminator. --- End quote --- If you were characterizing the probe and wanted to fairly assess whether it met its specifications for BW, etc, this would be correct. However, if you are just probing some circuit, you have to take it as it comes. My Tek P6139A looks entirely different then BillyO's, so I can't demonstrate with that. However, if you try it with a P6156 500R 10X, it looks good either way and just the amplitude changes. The reason 25R matters is that with 8pF and 500MHz, you get a calculated Z of only 40R, and of course the actual impedance of the probe is fairly complex at that point. I doubt that this signal is going to magically clean itself up with an extra 50R terminator, but I'll wait and see the result. |
| BillyO:
Results edited into reply #24. |
| bdunham7:
--- Quote from: BillyO on February 01, 2023, 02:30:08 am ---Results edited into reply #24. --- End quote --- That certainly made a lot of difference, and if you were looking to measure the rise time (characterizing re a spec) it should improve. But is it really better or more accurate or do you just dislike the aberrations less? Here is a P6156 500R 10X and a P6139A (doesn't look like yours, has a thread-on attenuator and can't use a BNC adapter at all, so all probing done by hand) without an extra terminator and then with one. |
| tautech:
--- Quote from: bdunham7 on February 01, 2023, 03:42:13 am ---Here is a P6156 500R 10X and a P6139A (doesn't look like yours, has a thread-on attenuator and can't use a BNC adapter at all, so all probing done by hand) without an extra terminator and then with one. --- End quote --- Nicely captured SMPS ripple on the max and min. ;) LED lighting ? |
| bdunham7:
--- Quote from: tautech on February 01, 2023, 03:52:42 am ---Nicely captured SMPS ripple on the max and min. ;) LED lighting ? --- End quote --- No, my LED lighting is now completely quiet. Besides, if that's noise it has got to be up around a GHz or so given that I'm at 20ns/div. Those are all single-shots, so you see stuff you might not otherwise. Perhaps it is internal, maybe ADC noise? |
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